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interest that herd protection after mass immunization eventually can wane over time, particularly where the immunogenicity of the vaccine does not allow for sustained antibody protection over time.This was evidenced by an outbreak of pertussis in Canada in 1990–1998 caused by a poorly protective whole cell vaccine [7]. It is sobering to note that after 30 y of intensive childhood immunization, there has been a recent re-emergence of adult pertussis, resulting in an increased risk of mortality in younger children [8]. The re-emergence of adult pertussis is likely due to a variety of factors, including waning vaccine immunity without a natural booster effect from household exposure, the loss of vaccine efficacy due to novel strains, and potentially also due to increased detection due to more sensitive diagnostic tests [9]. Reduced immunity among mothers has been particularly worrisome, as it has led to less effective transplacental immunity, increasing the vulnerability of young infants [10].

ces are restricted due to increasing resistance; therefore vaccines offer a potentially effective means to reduce invasive infections due to resistant strains. Currently there are 2 types of pneumococcal vaccine available: pneumococcal polysaccharide vaccines for adults and pneumococcal conjugate vaccines for children. The efficacy of the pneumococcal polysaccharide vaccine was first identified in young African gold miners in 1977 [17]. Based on these data, and data from similar studies, the World Health Organization has recommended pneumococcal polysaccharide vaccine for people aged ≥ 65 y and those at increased risk of pneumococcal disease since the early 1980s. However, more recently there has been considerable debate about the efficacy and effectiveness of the 23-valent pneumococcal polysaccharide vaccine in this elderly population [18]. Although the pneumococcal polysaccharide vaccine prevents invasive pneumococcal disease (odds ratio (OR) 0.26, 95% CI 0.15–0.46), there is no evidence that it prevents all-cause pneumonia [19]. Moreover, another recent systematic review has questioned the efficacy of the pneumococcal polysaccharide vaccine in preventing pneumococcal pneumonia among the currently indicated populations (risk ratio (RR) 1.04, 95% CI 0.78–1.38) [20].

% CI 0.15–0.46), there is no evidence that it prevents all-cause pneumonia [19]. Moreover, another recent systematic review has questioned the efficacy of the pneumococcal polysaccharide vaccine in preventing pneumococcal pneumonia among the currently indicated populations (risk ratio (RR) 1.04, 95% CI 0.78–1.38) [20]. Evidence exists that the elderly have indirectly benefited from the introduction of the pneumococcal conjugate vaccine in children. The US Centers for Disease Control and Prevention Active Bacterial Core Surveillance (1996 to 2001) demonstrated a reduction in invasive pneumococcal disease in those aged ≥65 y after the introduction of the 7-valent pneumococcal conjugate vaccine, despite the fact that this population did receive the vaccine (Figure 3) [21]. Therefore, increasing the coverage of childhood pneumococcal conjugate vaccine will potentially further protect the elderly. As a result of childhood immunization with 7-valent pneumococcal conjugate vaccine, the Active Bacterial Core Surveillance data demonstrated a herd effect in the elderly and a reduction by 49% (16.4 to 8.4 cases per 100,000) of antimicrobial-resistant (penicillin non-susceptible S. pneumoniae) invasive pneumococcal disease [22]. It has been recognized that in these studies, the most resistant strains were 6B, 9V, 9 A, 14, 19F and 23F, all of which were covered by the 7-valent pneumococcal conjugate vaccine. However, the emergence of non-7-valent pneumococcal conjugate vaccine serotypes such as 19A [23], reveals the potential for serotype switching and in fact reverse the herd effect. Therefore, it is important that future vaccines increase the number of strains they target to reduce this possibility. Indeed, studies are now underway to determine the potential impact of the 13-valent pneumococcal conjugate vaccine on the herd effect, as the 13-valent vaccine has recently replaced the 7-valent vaccine in many countries.

ure, the loss of vaccine efficacy due to novel strains, and potentially also due to increased detection due to more sensitive diagnostic tests [9]. Reduced immunity among mothers has been particularly worrisome, as it has led to less effective transplacental immunity, increasing the vulnerability of young infants [10]. The majority of pertussis-related deaths occur in infants aged < 3 months, thus a series of vaccinations is now recommended for children (2,4,6,15-18 months, and 4-6 y in the USA [11] and Canada [12]). Using a polymerase chain reaction, culture, and serological examination, an observational study demonstrated that the likely source of infection in infants was siblings (41%), mothers (38%), and fathers (17%) [13]. Therefore, to better protect infants through the herd effect, a programme of booster pertussis vaccination with decennial tetanus toxoid, has been implemented in adults. The reduction of laboratory-confirmed pertussis in adolescents and adults by a booster adult vaccination was supported by a placebo-controlled randomized trial of acellular pertussis vaccine conducted in 2781 healthy adolescents and adults, showing a vaccine efficacy of 92% (95% confidence interval (CI) 0.32-0.99) [14]. Although evidence for the herd effect due to decennial administration of acellular pertussis vaccine in young adults leading to a reduction in B. pertussis mortality in children is not yet available, this programme is recommended in many countries [15].

ine efficacy of 92% (95% confidence interval (CI) 0.32-0.99) [14]. Although evidence for the herd effect due to decennial administration of acellular pertussis vaccine in young adults leading to a reduction in B. pertussis mortality in children is not yet available, this programme is recommended in many countries [15]. Herd effects in pneumococcal vaccination Streptococcus pneumoniae causes both invasive (i.e. blood stream and other sterile sites) and non-invasive infection, such as community-acquired pneumonia. The burden of pneumococcal disease is high and is associated with significant morbidity and mortality. An estimated 1.6 million people, especially children aged < 5 y, die of invasive pneumococcal disease annually worldwide [16], thus prevention of this disease is of great importance. In addition, the optimal antibiotic therapeutic choices are restricted due to increasing resistance; therefore vaccines offer a potentially effective means to reduce invasive infections due to resistant strains. Currently there are 2 types of pneumococcal vaccine available: pneumococcal polysaccharide vaccines for adults and pneumococcal conjugate vaccines for children.

Introduction The direct effects of vaccination generally refer to the direct protection of the vaccinated individual, resulting in a reduced chance of infection and possibly complications. In contrast, the indirect benefits of vaccination refer to protective effects observed in unvaccinated populations [1]. This indirect effect of vaccination is known as the herd effect or ‘herd immunity’, defined as the indirect protection of unvaccinated persons, whereby an increase in the prevalence of vaccine-immunity prevents circulation of infectious agents in unvaccinated susceptible populations (Figure 1). Figure 1 Schematic presentation of the herd effect: The index patient transmits an infectious agent to a given number (basic reproductive number R0) of susceptible persons in the community. Black circles are infected persons and white circles are uninfected susceptible persons (panel A). After a mass immunization programme in the community (panel B), a proportion of the population is immunized (grey circles with ‘I’), thus directly protected from the infectious agent (direct effect). The immunized individuals further protect the susceptible population (white circles with ‘H’) by stopping the transmission within the social networks. This extra protection effect provided by a vaccine is called ‘herd immunity’.

(grey circles with ‘I’), thus directly protected from the infectious agent (direct effect). The immunized individuals further protect the susceptible population (white circles with ‘H’) by stopping the transmission within the social networks. This extra protection effect provided by a vaccine is called ‘herd immunity’. The importance of herd immunity was first recognized with smallpox, where the initial goal was to immunize 80% of the population in order to achieve such a herd effect. Although the ultimate eradication in 1977 was achieved with higher vaccine uptake rates, the herd effect contributed to the reduction of smallpox by a mass vaccination programme that focused on endemic countries [2]. Another important aspect of the herd effect is that it can play a key role in determining policy if it enhances cost-effectiveness. In the USA, it was estimated that the introduction of the quadrivalent meningococcal conjugate vaccine saved US$551 million in direct costs and $920 million in indirect costs, including costs associated with permanent disability and premature death [3]. Childhood pneumococcal vaccination is another example; the 7-valent pneumococcal conjugate vaccine was estimated to prevent 38,000 cases of invasive pneumococcal infection in the USA during its first 5 y of use at a cost of US$112,000 per life-y saved. However, the vaccine prevented 109,000 cases of invasive pneumococcal infection at a cost of $7500 per life-y saved when the herd effect was considered [4]. In the sections below, we review the experience of vaccination programmes and clinical trials in establishing a herd effect.

a cost of US$112,000 per life-y saved. However, the vaccine prevented 109,000 cases of invasive pneumococcal infection at a cost of $7500 per life-y saved when the herd effect was considered [4]. In the sections below, we review the experience of vaccination programmes and clinical trials in establishing a herd effect. Herd effects in Haemophilus influenzae type b vaccination Vaccination against invasive Haemophilus influenza type b with the conjugate vaccine began in high-income Scandinavian countries and resulted in a decline in invasive H. influenzae type b diseases in the vaccinated populations (0-4-y-olds: 49/100,000/y in 1986 to 0/100,000/y in 1996) with -95% effectiveness [5]. With a vaccine uptake of 50%, a herd effect appears to have occurred, as the reduction in invasive H. influenzae type b disease was also observed in unvaccinated older children (≥5 y) in Finland after the introduction of the H. influenzae type b conjugate vaccine in 1986 (Figure 2). Figure 2 The vaccine herd effect on Haemophilus influenzae type b diseases in Finland after introduction of the Haemophilus influenzae type b conjugate vaccine in 1986 (adapted from Peltola et al. [5]).

Herd effects in Haemophilus influenzae type b vaccination Vaccination against invasive Haemophilus influenza type b with the conjugate vaccine began in high-income Scandinavian countries and resulted in a decline in invasive H. influenzae type b diseases in the vaccinated populations (0-4-y-olds: 49/100,000/y in 1986 to 0/100,000/y in 1996) with -95% effectiveness [5]. With a vaccine uptake of 50%, a herd effect appears to have occurred, as the reduction in invasive H. influenzae type b disease was also observed in unvaccinated older children (≥5 y) in Finland after the introduction of the H. influenzae type b conjugate vaccine in 1986 (Figure 2). Figure 2 The vaccine herd effect on Haemophilus influenzae type b diseases in Finland after introduction of the Haemophilus influenzae type b conjugate vaccine in 1986 (adapted from Peltola et al. [5]). Herd effects in pertussis vaccination After the availability of pertussis vaccine in the 1940s, the introduction of pertussis immunization programmes with pertussis toxoid resulted in a sharp reduction in pertussis, not only among vaccinated infants, but also among non-vaccinated infants and older populations. For example, in a prospective study performed in Sweden, where the vaccine was only available after 1995 following an interruption of 16 y, there was a reduction in Bordetella pertussis isolation among non-vaccinated infants (1214 isolates between 1993 and 1995 to 64 isolates between 1997 and 1999; p < 0.0001). Moreover, pertussis-related hospitalization was reduced from 55 cases to 8 (population size 778,597) during the same time-periods (p < 0.0001) in the setting of an infant pertussis toxoid vaccine uptake of 56% [6]. It is of interest that herd protection after mass immunization eventually can wane over time, particularly where the immunogenicity of the vaccine does not allow for sustained antibody protection over time.This was evidenced by an outbreak of pertussis in Canada in 1990–1998 caused by a poorly protective whole cell vaccine [7].

ortant that future vaccines increase the number of strains they target to reduce this possibility. Indeed, studies are now underway to determine the potential impact of the 13-valent pneumococcal conjugate vaccine on the herd effect, as the 13-valent vaccine has recently replaced the 7-valent vaccine in many countries. Figure 3 The vaccine herd effect on invasive pneumococcal diseases in the USA after introduction of the 7-valent pneumococcal conjugate vaccine in children aged < 2 y in 2000 (adapted from Whitney et al. [21]). Herd effects in influenza vaccination Seasonal influenza is a major cause of mortality resulting in an estimated 36,000 deaths annually in the USA alone [24]. The annual vaccination policy against seasonal influenza in most countries has been focused on protecting groups at high risk for complications of influenza, including the elderly, pregnant women, young children, and individuals with chronic diseases. However, vaccinating high-risk populations is unlikely to reduce the burden of seasonal epidemics, because these groups represent only a fraction of the population among whom the virus spreads [25]. In addition, the attack rates in these groups are relatively low (8.8–13.5 per 100 persons for age ≥ 65 y). However, the attack rate is 25 per 100 persons in children aged 5–9 y and can reach 40 per 100 persons during pandemics, as experienced during 1918–19 [25].

on of the population among whom the virus spreads [25]. In addition, the attack rates in these groups are relatively low (8.8–13.5 per 100 persons for age ≥ 65 y). However, the attack rate is 25 per 100 persons in children aged 5–9 y and can reach 40 per 100 persons during pandemics, as experienced during 1918–19 [25]. Another challenge with only vaccinating high-risk groups is that the vaccines may not work as well in these at-risk populations. The efficacy of the influenza vaccine is dependent on the immunological status of the specific population being vaccinated and on the type of vaccine. For example, in healthy children, pooled estimates suggest that the live attenuated vaccine leads to a 79% efficacy (absolute risk reduction (ARR) 152.4 per 1000, number needed to treat (NNT) 6.6 persons) for reducing laboratory-confirmed influenza with 38% efficacy for reducing symptoms [26]. In contrast, in the elderly, no significant direct benefit of routine inactivated trivalent influenza vaccine was observed against influenza (RR 1.04, 95% CI 0.43–2.51) [26]. Of note, however, well-matched vaccines prevented complications in residents of long-term care facilities (vaccine efficacy (VE) of hospital admission 45%, 95% CI 0.16-0.64; all-cause mortality 60%, 95% CI 0.23–0.79) [27]. It is likely that the relative ineffectiveness of inactivated influenza vaccine in the elderly population is due to immune senescence, a waning of the immune system with age [28, 29].

erm care facilities (vaccine efficacy (VE) of hospital admission 45%, 95% CI 0.16-0.64; all-cause mortality 60%, 95% CI 0.23–0.79) [27]. It is likely that the relative ineffectiveness of inactivated influenza vaccine in the elderly population is due to immune senescence, a waning of the immune system with age [28, 29]. The fact that groups at the highest risk of complications from infection often benefit the least from the vaccine is an important public health and scientific challenge. Providing an indirect benefit to these groups by vaccinating those who respond well to vaccines is one way to mitigate this public health challenge. Data exist that a herd effect due to vaccination in children may help protect high-risk groups [30-32]. Recently, a cluster randomized study of trivalent inactivated influenza vaccination administered to 947 children and adolescents in Hutterites colonies in Canada showed a dramatic herd effect.The protective effectiveness in non-recipients of study vaccine was 61% (95% CI 0.08–0.83; p = 0.03) for reducing laboratory-confirmed influenza (3.1% in unvacci-nated adults of vaccinated colonies vs 7.6% in unvaccinated colonies; ARR 40.0 per 1000, NNT 25.0 persons; Figure 4) [32]. Such data lead to other important questions that still need to be answered, including the cost-effectiveness of vaccinating healthy children, the minimum uptake of vaccine in children needed to show a herd effect, and whether universal influenza vaccination is cost-effective. As has been demonstrated by Finnish researchers, the influenza vaccine is cost-effective when administered to children aged 6–13 y when considering the direct benefits of the vaccine [33]. Since there is now evidence that a benefit of up to 60% effectiveness may be seen in unvaccinated individuals due to the herd effect [32], this argues for an even greater cost-effectiveness of immunizing children.

ective when administered to children aged 6–13 y when considering the direct benefits of the vaccine [33]. Since there is now evidence that a benefit of up to 60% effectiveness may be seen in unvaccinated individuals due to the herd effect [32], this argues for an even greater cost-effectiveness of immunizing children. Figure 4 The vaccine herd effect on influenza in a randomized control trial in Canada (adapted from Loeb et al. [32]). The Society for Healthcare Epidemiology of America recently released a statement that influenza vaccination of healthcare personnel is a core patient and healthcare personnel safety practice [34]. Whether vaccination of healthcare personnel can lead to a herd effect reducing laboratory-confirmed influenza among patients is still inconclusive. Pooled data from a Cochrane review of 3 cluster randomized controlled trials showed no reduction of laboratory-confirmed influenza (OR 0.86, 95% CI 0.44–1.68; p = 0.66), lower respiratory tract infections, admission to hospital (OR 0.89, 95% CI 0.75–1.06), and deaths from pneumonia (OR 0.82, 95% CI 0.45–1.49) in patients when healthcare personnel were vaccinated [35]. However, given that mathematical models suggest a herd effect [36], more rigorous studies need to be conducted.

0.66), lower respiratory tract infections, admission to hospital (OR 0.89, 95% CI 0.75–1.06), and deaths from pneumonia (OR 0.82, 95% CI 0.45–1.49) in patients when healthcare personnel were vaccinated [35]. However, given that mathematical models suggest a herd effect [36], more rigorous studies need to be conducted. Herd effects in meningococcal vaccination Meningococcal meningitis causes devastating epidemics in sub-Saharan Africa where vaccine prevention is most needed. Because most meningococcal infections are caused by 6 of the 13 known serogroups (A, B, C, W-135, X, Y), these epidemics are preventable by vaccine. In 1991, a school-based cluster randomized double-blind trial of a serogroup B meningococcal vaccine that involved 171,800 students resulted in a vaccine efficacy of 71% [37]. Although this trial was performed in Norway, which had a high incidence of serogroup B meningococcal disease [38, 39], it failed to demonstrate a reduction in meningococcal disease among unvaccinated children in the vaccinated clusters. Evidence of a vaccine herd effect was suggested after adoption of routine monovalent serogroup C meningococcal vaccination in infants in England in 1999, where the incidence of meningococcal serogroup C disease declined not only in the vaccine group, but also in unvaccinated groups (by 67% in those aged 1–17 y and 35% in those aged >25 y) [40]. During the same period, carriage of serogroup C meningococci was reduced by 66% (p = 0.004) according to data collected from 14,064 students aged 15–17 y at the time of vaccination, and 16,583 students 1 y later [41].

group, but also in unvaccinated groups (by 67% in those aged 1–17 y and 35% in those aged >25 y) [40]. During the same period, carriage of serogroup C meningococci was reduced by 66% (p = 0.004) according to data collected from 14,064 students aged 15–17 y at the time of vaccination, and 16,583 students 1 y later [41]. Although nasal carriage is the basic step for invasive infection, the relationship between acquisition (carriage) and infection is not yet clear. Neisseria meningitidis commonly (∼10%) colonizes the human oropharyngeal mucosa, and asymptomatic carriage is perennial occurring with a high frequency in teenagers where there is substantial genetic diversity of strains that are isolated [42]. Symptomatic infections on the other hand are seasonal and occur more commonly in younger children [42]. Quadrivalent (A, C, Y, W-135) vaccines are licensed in the USA for those aged 11–18 y and in persons aged 2–55 y who are at elevated risk for invasive meningococcal disease [43]. Active surveillance in the USA for invasive N. meningitidis during 1998–2007 showed a 64.1% reduction in the annual incidence, from 0.92 cases per 100,000 population in 1998 to 0.33 cases per 100,000 population in 2007 [44].

y and in persons aged 2–55 y who are at elevated risk for invasive meningococcal disease [43]. Active surveillance in the USA for invasive N. meningitidis during 1998–2007 showed a 64.1% reduction in the annual incidence, from 0.92 cases per 100,000 population in 1998 to 0.33 cases per 100,000 population in 2007 [44]. Herd effects in rotavirus vaccination Rotavirus is now the most important cause of gastroenteritis in young children (age < 5 y) [45]. Since natural infection caused by a single serotype in infancy results in protection against subsequent infection by both homotypic and heterotypic viruses [46], vaccination against certain serotypes alone might reduce the burden of rotavirus infection. Several vaccines have proven efficacy and safety [47].

5 y) [45]. Since natural infection caused by a single serotype in infancy results in protection against subsequent infection by both homotypic and heterotypic viruses [46], vaccination against certain serotypes alone might reduce the burden of rotavirus infection. Several vaccines have proven efficacy and safety [47]. In addition, a herd benefit of rotavirus vaccine is suggested by laboratory-based surveillance data [48] and mathematical modelling [49]. With an estimated vaccination rate of ∼50% in the USA with pentavalent rotavirus vaccine, an 87% reduction in cases was observed from the hospital-based population surveillance during the outbreak seasons following introduction of the vaccine. According to the mathematical models, the predicted additional protection of rotavirus-related gastroenteritis by vaccine herd effect was 25%, 22%, and 20% with vaccine uptake rates of 70%, 90%, and 95%, respectively. A herd benefit was also suggested in Nicaragua by observing the reduction of acute gastroenteritis following adoption of free rotavirus vaccine for all eligible children [50]. The World Health Organization recently recommended that rotavirus vaccine be included in the immunization programmes of countries where data on vaccine efficacy suggest a significant public health impact. However, since the highest mortality rates occur in sub-Saharan Africa and South Asia, further evidence of direct and indirect effects should be sought in these countries [51].

irus vaccine be included in the immunization programmes of countries where data on vaccine efficacy suggest a significant public health impact. However, since the highest mortality rates occur in sub-Saharan Africa and South Asia, further evidence of direct and indirect effects should be sought in these countries [51]. Potential herd effects in human papillomavirus (HPV) vaccination Human papillomavirus (HPV), although not a notifiable disease, is considered the most common agent of sexually transmitted infection given the high global incidence of HPV DNA in sexually active women [52]. A meta-analysis of 157,879 women with normal cervical cytology approximates the prevalence of HPV DNA to be 10.4% (95% CI 10.2–10.7%) [53]. Persistent HPV infection is the greatest risk factor for the development of high-grade precancerous lesions or invasive cervical cancer. The burden of HPV infection, along with cervical cancer mortality, appears to be even higher in developing countries [54]. Even within the context of a decreasing incidence of cervical cancer in resource-rich countries, where effective screening programmes and promotion of condom use are in place, vaccination against certain subtypes of HPV has proven effective in the prevention of the HPV infection and precancerous cervical disease [55]. The direct effect was supported by a meta-analysis of 6 randomized controlled studies, showing a reduced frequency of high-grade cervical lesion by an OR of 0.14 (95% CI 0.09–0.21) [56].

n against certain subtypes of HPV has proven effective in the prevention of the HPV infection and precancerous cervical disease [55]. The direct effect was supported by a meta-analysis of 6 randomized controlled studies, showing a reduced frequency of high-grade cervical lesion by an OR of 0.14 (95% CI 0.09–0.21) [56]. Although these vaccines are recommended in developed countries, the field efficacy and indirect benefits, including the herd effect of HPV vaccination, remain unknown. There is still debate about the cost-effectiveness of such expensive vaccines compared to the usual screening and promotion of condom use in resource-limited countries [57]. However, with the high efficacy of the vaccine against cervical cancer, a vaccine herd effect might be expected, especially in high endemic regions. At present, a benefit has only been shown through mathematical modelling [58]. Moreover, the effect of a vaccine herd effect in women by vaccinating men, or vice versa, has not yet been proven.

efficacy of the vaccine against cervical cancer, a vaccine herd effect might be expected, especially in high endemic regions. At present, a benefit has only been shown through mathematical modelling [58]. Moreover, the effect of a vaccine herd effect in women by vaccinating men, or vice versa, has not yet been proven. Conclusions In summary, we have shown that the benefits of many current vaccines extend beyond the direct benefits to indirect benefits, i.e. through the herd effect extending beyond targeted groups to other populations at high risk for complications. Nevertheless, gaps in our knowledge exist about how best to achieve herd immunity. For example, it is unclear whether there are particular formulations that confer better herd immunity than others; a prime example is whether herd immunity achieved through live attenuated influenza vaccine is superior to that achieved with inactivated vaccine. Another area where gaps in our knowledge exist is the optimal use of new vaccines. For example, there are several candidate vaccines for dengue in clinical trials and strategies for how best to use them to establish herd immunity need to be developed. Declaration of interest The authors declare no conflict of interest.

Introduction Infection of cells in the central nervous system (CNS) is a general aspect of systemic human immunodeficiency virus (HIV) infection. While combination antiretroviral therapy (cART) has effectively reduced the more severe neurological complications of HIV infection, milder forms of cognitive impairment are often still present in treated subjects [1,2], although the real prevalence is the subject of debate [3]. The traditionally used treatment regimens containing 2 nucleoside reverse transcriptase inhibitors (NRTI) together with either a non-nucleoside reverse transcriptase inhibitor (NNRTI) or a ritonavir-boosted protease inhibitor (PI/r) most often have good effects in the CNS, with a suppressive effect on the cerebrospinal fluid (CSF) viral load, intrathecal immunoactivation, and markers of brain damage [4–6].

nhibitors (NRTI) together with either a non-nucleoside reverse transcriptase inhibitor (NNRTI) or a ritonavir-boosted protease inhibitor (PI/r) most often have good effects in the CNS, with a suppressive effect on the cerebrospinal fluid (CSF) viral load, intrathecal immunoactivation, and markers of brain damage [4–6]. Switching to PI/r monotherapy after achieving HIV RNA suppression by traditional cART has been demonstrated to have high efficacy for maintaining viral suppression in the blood [7,8]. PI/r monotherapy, mainly ritonavir-boosted darunavir (DRV/r), is increasingly used as maintenance therapy in parts of Europe. The main reasons for this are to avoid NRTI toxicity and to reduce treatment costs [9]. In the latest European AIDS Clinical Society (EACS) guidelines, PI/r monotherapy is considered an option in patients with intolerance to NRTI or for treatment simplification in patients without a history of failure on prior PI-based therapy and who have been virologically suppressed for at least 6 months (http://www.europeanaidsclinicalsociety.org/images/stories/EACS-Pdf/eacsguidelines-v6_english.pdf)). Concerns about the efficacy of PI/r monotherapy in preventing HIV replication in the CNS have, however, been raised.

of failure on prior PI-based therapy and who have been virologically suppressed for at least 6 months (http://www.europeanaidsclinicalsociety.org/images/stories/EACS-Pdf/eacsguidelines-v6_english.pdf)). Concerns about the efficacy of PI/r monotherapy in preventing HIV replication in the CNS have, however, been raised. Here we report 2 subjects on DRV/r monotherapy with CSF viral breakthrough together with increased CNS immunoactivation and signs of neuronal damage. Both were part of an ongoing prospective research cohort, currently containing more than 1500 CSF samples from more than 400 HIV-infected subjects, and the only subjects in the cohort on DRV/r monotherapy maintenance therapy. The study was approved by the regional ethics review board of Gothenburg and patients have provided informed consent for participation.

research cohort, currently containing more than 1500 CSF samples from more than 400 HIV-infected subjects, and the only subjects in the cohort on DRV/r monotherapy maintenance therapy. The study was approved by the regional ethics review board of Gothenburg and patients have provided informed consent for participation. Case reports Case 1 The first case is that of a black woman born in 1985 and diagnosed with HIV during pregnancy in 2007. Her CD4 count was 170 cells/μl at diagnosis and she started treatment in May 2007 with zidovudine (ZDV), lamivudine (3TC), and lopinavir/ritonavir (LPV/r). The plasma HIV RNA level (Taqman, Roche) decreased from 82,400 to < 20 copies/ml after approximately 3 months of treatment and remained undetectable thereafter (Figure 1). In April 2009 her treatment regimen was changed to abacavir (ABC), 3TC, and DRV/r 800/100 mg once daily. ABC and 3TC were stopped in August 2009 because of a rash and she continued with DRV/r as monotherapy. The rash was mild and probably not associated with ABC-induced hypersensitivity syndrome; she does not carry the HLA-B*5701 allele. A lumbar puncture was performed as part of the study protocol approximately 4 months later and showed a viral load of 119 copies/ml in blood and 709 copies/ml in CSF. At the same time she had an increased CSF lymphocyte count (30 cells/μl, normal < 3) and increased CSF beta-2 microglobulin (2.6 mg/l, normal < 1.2; nephelometry) and CSF neopterin (40.5 nmol/l, normal < 5.8; ELISA/RIA BRAHMS) as markers of macrophage/microglial activation [4]. Furthermore, we found an increased CSF concentration of the light subunit of neurofilament (NFL), a sensitive marker of axonal damage (600 ng/l, normal < 380, age- related; ELISA, UmanDiagnostics) [10]. No primary resistance mutations were found on sequencing of the virus from plasma or CSF. Subsequently, tenofovir (TDF) and emtricitabine (FTC) were added to DRV/r and her plasma viral load decreased to < 20 copies/ml again within 1 month. Another lumbar puncture was performed 4 months later and at that time her CSF viral load had decreased to 56 copies/ml. The CSF beta-2 microglobulin had decreased to 1.6 mg/l, CSF neopterin concentration to 6.9 nmol/l, and CSF NFL had normalized (360 ng/l). She did not experience any neurological or cognitive symptoms during this time period or after, but no neuropsychological testing was done.

viral load had decreased to 56 copies/ml. The CSF beta-2 microglobulin had decreased to 1.6 mg/l, CSF neopterin concentration to 6.9 nmol/l, and CSF NFL had normalized (360 ng/l). She did not experience any neurological or cognitive symptoms during this time period or after, but no neuropsychological testing was done. Figure 1. Two cases of CSF escape during darunavir/r monotherapy (period shaded). Upper panels show cerebrospinal fluid (CSF) and plasma (P) HIV RNA together with treatment history; time 0 represents first initiation of antiretroviral treatment; dotted lines correspond to 50 copies/ml. Lower panels show CSF neopterin and neurofilament light protein (NFL) concentrations; dotted lines represent upper normal limits.

how cerebrospinal fluid (CSF) and plasma (P) HIV RNA together with treatment history; time 0 represents first initiation of antiretroviral treatment; dotted lines correspond to 50 copies/ml. Lower panels show CSF neopterin and neurofilament light protein (NFL) concentrations; dotted lines represent upper normal limits. Case 2 The second case is that of a Caucasian man born in 1961 who was diagnosed with HIV in 2001 when presenting with a peripheral facial palsy; he recovered fully from the palsy within 5 months. His CD4 count decreased from 390 to 160 cells/μl within the first 3 y and he started cART in 2004 with ZDV, 3TC, and LPV/r. In 2009 he participated in a treatment intensification study [11] and received in addition to his other cART ,4 weeks enfuvirtide and 4 weeks maraviroc, followed by his previous treatment regimen. Because of side effects, he changed treatment in August 2009 to ABC, 3TC, and DRV/r. In November 2010 he simplified his treatment to DRV/r monotherapy 800/100 mg once daily. His plasma viral load remained below 50 copies/ml from when he was first suppressed in May 2005 throughout his entire treatment history, and his CD4 count increased to 790 cells/μl. Lumbar punctures were performed in total 15 times in the prospective study, including 2 performed before treatment initiation (Figure 1). All 11 CSF samples taken during the period on cART showed a CSF viral load < 50 copies/ml. Thereafter, lumbar punctures were performed after 3 and 12 months of DRV/r monotherapy; at the second time point the viral load had increased to 478 copies/ml in CSF, while it was 46 copies/ml in plasma. There were also signs of increased intrathecal immunoactivation with elevated CSF lymphocyte count (17 cells/μl), CSF beta-2 microglobulin (1.6 mg/l), and CSF neopterin (9.4 nmol/l). Furthermore, we found an increased CSF NFL concentration (1530 ng/l, normal < 890, age-related), but while the increased CSF viral load and intrathecal immunoactivation developed first after switching to DRV/r monotherapy, increased NFL had also been present before. No symptoms or complaints arose and he remained normal on neuropsychological testing by CogState (detection, identification, 1 card learning, 1 back speed, 1 back accuracy) [12] when examined before and 12 months after changing to DRV/r monotherapy. No primary resistance mutations were found in blood or CSF.

nt before. No symptoms or complaints arose and he remained normal on neuropsychological testing by CogState (detection, identification, 1 card learning, 1 back speed, 1 back accuracy) [12] when examined before and 12 months after changing to DRV/r monotherapy. No primary resistance mutations were found in blood or CSF. He was reintroduced to ABC, 3TC, and DRV/r, and the plasma viral load decreased to < 20 copies/ml within 1 month. A lumbar puncture was performed after 3 months and his CSF viral load had decreased to < 20 copies/ml again. CSF neopterin was not analyzed at that time, but both beta-2 microglobulin (1.4 mg/l) and the CSF lymphocyte count (< 3 cells/μl) had decreased. However, the CSF NFL concentration continued to be increased (2410 ng/l). Discussion PI/r monotherapy maintenance regimens, mainly with DRV/r, are increasingly being used in parts of the world, and its effect on the systemic infection has been shown to be satisfactory. However, the 2 cases presented here raise concerns about the effects of DRV/r monotherapy on HIV CNS infection. In the MONOI study, 2 patients who were virologically suppressed in plasma developed mild neurological symptoms, and when a lumbar puncture was done they were both found to have CSF escape (330 and 580 copies/ml) [8]. Together, these cases suggest that DRV/r monotherapy should be used with caution until the results of studies on CSF are available. Concerns have also been raised regarding monotherapy with other PIs, i.e. atazanavir/r and lopinavir/r [13,14].

as done they were both found to have CSF escape (330 and 580 copies/ml) [8]. Together, these cases suggest that DRV/r monotherapy should be used with caution until the results of studies on CSF are available. Concerns have also been raised regarding monotherapy with other PIs, i.e. atazanavir/r and lopinavir/r [13,14]. As well as viral CSF breakthrough and intrathecal immunoactivation with pleocytosis and increased markers of macrophage/microglial activation (beta-2 microglobulin and neopterin), signs of neuronal damage with increased CSF NFL levels were found in both our subjects. As a comparison, increased CSF NFL was found in only 1 out of 38 samples drawn from 21 subjects on cART that included DRV/r in our research cohort (data not shown). It has to be noted that in one of the reported cases, NFL was already increased before switching to DRV/r monotherapy and also continued to be increased after the reintroduction of ABC/3TC. The reason for this is unknown and increased CSF NFL concentrations could not be ascribed to the DRV/r monotherapy in this subject. NFL is a very sensitive marker of neuronal destruction and increased levels can, for example, be found in various types of dementia, cerebrovascular disease, and in a variety of neurodegenerative disorders [10]. Increased CSF NFL levels are also consistently found in HIV-associated dementia, often in very high concentrations [15]. We have also found CSF NFL to be a good predictive marker with increased concentrations in asymptomatic patients who subsequently develop HIV-associated dementia [16].

urodegenerative disorders [10]. Increased CSF NFL levels are also consistently found in HIV-associated dementia, often in very high concentrations [15]. We have also found CSF NFL to be a good predictive marker with increased concentrations in asymptomatic patients who subsequently develop HIV-associated dementia [16]. Despite ongoing brain injury, none of the subjects in this report developed any neurological symptoms. However, both were closely followed and changed their treatment to include NRTIs; we do not know what would have happened if they had continued on DRV/r monotherapy. Several cases on effective cART who have developed neurological symptoms and who have been shown to have concomitant CSF escape have recently been reported [17]; many of these patients were on atypical or incomplete ART regimens when they became neurosymptomatic and were discovered to have CSF/plasma discordance. An increased CSF viral load can also be found in approximately 10% of virologically suppressed neurologically asymptomatic patients with more conventional antiretroviral regimens [18]. However, CSF HIV RNA in such cases is only slightly increased (< 200 copies/ml) and might represent CSF viral ‘blips’. It is intriguing that the only 2 cases on DRV/r monotherapy that we examined both had CSF viral breakthrough and increased intrathecal immunoactivation. The longitudinal progress of CSF viral breakthrough is not known, nor are the potential clinical consequences. Until better studied, we suggest caution in using PI/r monotherapy and other experimental ART combinations outside clinical studies.

both had CSF viral breakthrough and increased intrathecal immunoactivation. The longitudinal progress of CSF viral breakthrough is not known, nor are the potential clinical consequences. Until better studied, we suggest caution in using PI/r monotherapy and other experimental ART combinations outside clinical studies. Declaration of interest: This work was supported by the Swedish Research Council (K2008-58P-20930-04-1, K2008-58X-20931-01-1, K2010-63P-21562-01-4, and K2011-61X-20401-05-6) and the Sahlgrenska Academy at the University of Gothenburg (ALFGBG-141741 and ALFGBG-144341). MG has received lecture fees from and/or participated on scientific advisory boards for Abbott, Boehringer-Ingelheim, Bristol-Myers Squibb, Gilead Sciences, GlaxoSmithKline, Jansen/Tibotec, Merck, and Pfizer. LH has received lecture fees from Abbott and Roche and has participated on scientific advisory boards for Pfizer and Meda. BS has received research grants from Chrontech Pharma (former Tripep AB) and GlaxoSmithKline. DF and HZ declare no competing interests.

Introduction From around the year 2000, Northern Europe experienced a rise in superficial skin infections, most often diagnosed as impetigo. In many cases the infections were caused by Staphylococcus aureus resistant to fusidic acid [1,2]. In 2003, O’Neill and collaborators identified a single clone of S. aureus as being the bacterial pathogen involved in the impetigo outbreak in Norway, Sweden, the UK and Ireland [3]. They termed this clone ‘the epidemic European fusidic acid-resistant impetigo clone’ (EEFIC), and later performed a comprehensive molecular characterization of the clone [4]. Several studies documented the presence of the EEFIC being related to elevated numbers of impetigo cases in Norway [1], Sweden [2], the UK and Ireland [3]. Later, the presence of the clone was also confirmed in France [5] and the Netherlands [6]. In 2011, we reported data on the incidence and bacteriology of impetigo in the Norwegian island community of Austevoll during the years 2001–2009 [7]. Phenotypic characteristics of the bacteria were determined for the whole period, and in 2008 and 2009 molecular analyses were performed on selected isolates. The prevalence of the EEFIC was much less in 2009 than in 2008, indicating an attenuation of the impetigo epidemic caused by the EEFIC. Further suggestions of a decrease of the EEFIC came from studies from Sweden [8] and Denmark [9], showing falling rates of fusidic acid resistance in impetigo-related S. aureus isolates in the latter half of the first decade after the year 2000.

8, indicating an attenuation of the impetigo epidemic caused by the EEFIC. Further suggestions of a decrease of the EEFIC came from studies from Sweden [8] and Denmark [9], showing falling rates of fusidic acid resistance in impetigo-related S. aureus isolates in the latter half of the first decade after the year 2000. In the current study, we wanted to explore indications of an end to the impetigo epidemic caused by the EEFIC in the community of Austevoll, Norway, based on continued data for the years 2010–2012. Materials and methods The study was performed during the years 2001–2012 in the island municipality of Austevoll, Western Norway. The municipality had a mean population of 4400 inhabitants during the study period. The connection to the mainland is by boats and ferries only. During the study period the mean number of general practitioners (GPs) in the municipality was four. The GPs share a common Electronic Patient Journal (EPJ) system, and they agreed to record all cases of impetigo in a uniform way. Impetigo was defined as a superficial skin infection with spontaneous eruption of erosions being covered by honey-coloured crusts. The GPs were encouraged to take bacterial specimens from all impetigo cases. The bacterial specimens were sent to the Department of Microbiology, Haukeland University Hospital, Bergen, Norway. Annual incidence of impetigo was calculated and epidemic season was defined according to a standard procedure [10].

red crusts. The GPs were encouraged to take bacterial specimens from all impetigo cases. The bacterial specimens were sent to the Department of Microbiology, Haukeland University Hospital, Bergen, Norway. Annual incidence of impetigo was calculated and epidemic season was defined according to a standard procedure [10]. In addition, the project leader (S.R.), who was one of the community GPs, collected bacterial specimens from cases of other bacterial skin infections, for comparison with the impetigo cases. These non-impetigo specimens were not collected according to specific criteria. Bacteria in all specimens were detected and identified by standard methods. The susceptibility of S. aureus to penicillin G, oxacillin, erythromycin, fusidic acid and clindamycin was determined using disc diffusion tests. From December 2012 antimicrobial susceptibility testing (AST) was done according to the EUCAST disc diffusion method. Before this, AST was done according to the Norwegian Working Group on Antibiotics (NWGA). Before the laboratory changed the method for susceptibility testing, the two methods were compared. Regarding susceptibility categorization (sensitive/intermediate/resistant), the two methods were found to be comparable.

n method. Before this, AST was done according to the Norwegian Working Group on Antibiotics (NWGA). Before the laboratory changed the method for susceptibility testing, the two methods were compared. Regarding susceptibility categorization (sensitive/intermediate/resistant), the two methods were found to be comparable. Molecular epidemiological typing was performed on available S. aureus isolates in the period 2008–2012. Both pulsed-field gel electrophoresis (PFGE) and staphylococcal protein A typing (spa-typing) were used. Although different, the methods are thought to be comparable when it comes to classifying an isolate as belonging to the EEFIC clone or not. In this period, 83 impetigo cases were registered, 77 swabs were taken and S. aureus was isolated in 52 cases. In the years 2008–2009, all available impetigo S. aureus isolates (n = 28) were investigated by PFGE. Band patterns were compared visually and differences were evaluated as described by Tenover et al. [11]. Isolates indicated by PFGE to belong to the EEFIC (n = 11), and fusidic acid-resistant (FAR) isolates not found by PFGE to be related to the EEFIC (n = 2), were further analysed by spa typing, which was performed at St Olavs Hospital, Trondheim, Norway, as described previously [12]. In the years 2010–2012, the PFGE method was no longer an available laboratory method. In this period, all available impetigo S. aureus isolates (n = 16) were investigated by spa typing instead. A few impetigo S. aureus isolates (6 of 34 isolates from 2008–2009 and 2 of 18 from 2010–2012) were lost to further molecular analyses.

ars 2010–2012, the PFGE method was no longer an available laboratory method. In this period, all available impetigo S. aureus isolates (n = 16) were investigated by spa typing instead. A few impetigo S. aureus isolates (6 of 34 isolates from 2008–2009 and 2 of 18 from 2010–2012) were lost to further molecular analyses. By PFGE analysis, all 11 non-impetigo S. aureus isolates in the years 2008–2009 were found not to be related to the EEFIC, and were not subjected to further spa typing. Nineteen non-impetigo S. aureus isolates from 2010–2012 were all sent for spa typing. To be defined as EEFIC in the present study, isolates had to show spa typing at least closely related to the EEFIC reference strain (spa type t171) [1,3,4]. Continuous surveillance of the impetigo incidence and FAR S. aureus prevalence has been the main focus of the Austevoll impetigo study. We have previously documented falling rates of these variables since the start of the epidemic in 2002–2003 and forward up to 2009 [10]. We retrospectively collected data on prevalence and bacteriology of impetigo cases for the last half of 2001. To investigate a possible end to the EEFIC- related impetigo epidemic in Austevoll, we here present the data for the years 2010–2012 as an extension of the data from the previous years. For overview, we also present some previously published data. Ethics Ethics approval was obtained from the Regional Committee for Medical and Health Research Ethics of Western Norway, and the study was also approved by the Ombudsman for Privacy in Research, Norwegian Social Science Data Services.

To investigate a possible end to the EEFIC- related impetigo epidemic in Austevoll, we here present the data for the years 2010–2012 as an extension of the data from the previous years. For overview, we also present some previously published data. Ethics Ethics approval was obtained from the Regional Committee for Medical and Health Research Ethics of Western Norway, and the study was also approved by the Ombudsman for Privacy in Research, Norwegian Social Science Data Services. Results In total, 484 impetigo cases were registered, and bacterial specimens were collected from 388 of these cases. Table I shows the annual incidence of impetigo for the period 2001–2012. After a maximum in 2002, there was a marked decline in incidence, and there was no epidemic season after 2004 [10]. Altogether, bacterial swabs were taken from 80% of the patients, and S. aureus was grown in 76% of the cases where swabs were taken (Table I). The proportion of FAR S. aureus isolates decreased during the period 2002–2009, with a mean of 80% in the epidemic years 2002–2004, 55% in 2005–2009 [7]. The decline continued and reached 6% in 2010–2012. These declining trends are depicted in Figure 1. Figure 1. Number of impetigo cases, S. aureus isolates in impetigo and fusidic acid-resistance in S. aureus in impetigo, in Austevoll 2002–2012. Table I. Yearly incidence rates and microbial characteristics of impetigo in the total population of Austevoll, Western Norway (n = 4400)a.

Results In total, 484 impetigo cases were registered, and bacterial specimens were collected from 388 of these cases. Table I shows the annual incidence of impetigo for the period 2001–2012. After a maximum in 2002, there was a marked decline in incidence, and there was no epidemic season after 2004 [10]. Altogether, bacterial swabs were taken from 80% of the patients, and S. aureus was grown in 76% of the cases where swabs were taken (Table I). The proportion of FAR S. aureus isolates decreased during the period 2002–2009, with a mean of 80% in the epidemic years 2002–2004, 55% in 2005–2009 [7]. The decline continued and reached 6% in 2010–2012. These declining trends are depicted in Figure 1. Figure 1. Number of impetigo cases, S. aureus isolates in impetigo and fusidic acid-resistance in S. aureus in impetigo, in Austevoll 2002–2012. Table I. Yearly incidence rates and microbial characteristics of impetigo in the total population of Austevoll, Western Norway (n = 4400)a. Year Impetigo cases n Incidence Per 1000 person-years Swabs taken Growth of S. aureus n (%) Fus resb n (%) PFGE performed spa typing performed EEFIC isolates Non-EEFIC isolates n (%) Fus res n (%) Fus sens n (%) Fus res n (%) Fus sens n (%)

Table I. Yearly incidence rates and microbial characteristics of impetigo in the total population of Austevoll, Western Norway (n = 4400)a. Year Impetigo cases n Incidence Per 1000 person-years Swabs taken Growth of S. aureus n (%) Fus resb n (%) PFGE performed spa typing performed EEFIC isolates Non-EEFIC isolates n (%) Fus res n (%) Fus sens n (%) Fus res n (%) Fus sens n (%) 2001c 20 0.0091 10 (50) 9 (90) 6 (67) 2002d 115 0.0260 90 (78) 75 (83) 65 (87) 2003d 85 0.0192 63 (74) 47 (74) 33 (70) 2004d 72 0.0163 53 (74) 46 (87) 37 (80) 2005 42 0.0095 39 (93) 24 (62) 11 (46) 2006 42 0.0100 38 (90) 27 (71) 16 (59) 2007 25 0.0057 18 (72) 16 (89) 13 (81) 2008 35 0.0079 35 (100) 25 (71) 11 (44) 21 9 8 (89) 1 (11) 0 (0) 12 (100) 2009 17 0.0038 15 (88) 9 (60) 5 (56) 7 4 2 (100) 0 (0) 2 (40) 3 (60) 2010 11 0.0025 10 (91) 7 (70) 1 (14) 6 0 (0) 0 (0) 1 (17) 5 (83) 2011 7 0.0016 7 (100) 4 (57) 0 (0) 4 0 (0) 0 (0) 0 (0) 4 (100) 2012 13 0.0029 10 (77) 7 (70) 0 (0) 6 0 (0) 0 (0) 0 (0) 6 (100) EEFIC, epidemic European fusidic acid-resistant impetigo clone; Fus res, resistance to fusidic acid; Fus sens, sensitive to fusidic acid; PFGE, pulsed-field gel electrophoresis. aData from the period 2001–2009 have been published previously [7,10]. bProportion of swabs with fusidic acid resistance per number of swabs with S. aureus isolates. cIn 2001 impetigo was registered for the last half year. dYears of epidemic impetigo outbreak [10].

2001c 20 0.0091 10 (50) 9 (90) 6 (67) 2002d 115 0.0260 90 (78) 75 (83) 65 (87) 2003d 85 0.0192 63 (74) 47 (74) 33 (70) 2004d 72 0.0163 53 (74) 46 (87) 37 (80) 2005 42 0.0095 39 (93) 24 (62) 11 (46) 2006 42 0.0100 38 (90) 27 (71) 16 (59) 2007 25 0.0057 18 (72) 16 (89) 13 (81) 2008 35 0.0079 35 (100) 25 (71) 11 (44) 21 9 8 (89) 1 (11) 0 (0) 12 (100) 2009 17 0.0038 15 (88) 9 (60) 5 (56) 7 4 2 (100) 0 (0) 2 (40) 3 (60) 2010 11 0.0025 10 (91) 7 (70) 1 (14) 6 0 (0) 0 (0) 1 (17) 5 (83) 2011 7 0.0016 7 (100) 4 (57) 0 (0) 4 0 (0) 0 (0) 0 (0) 4 (100) 2012 13 0.0029 10 (77) 7 (70) 0 (0) 6 0 (0) 0 (0) 0 (0) 6 (100) EEFIC, epidemic European fusidic acid-resistant impetigo clone; Fus res, resistance to fusidic acid; Fus sens, sensitive to fusidic acid; PFGE, pulsed-field gel electrophoresis. aData from the period 2001–2009 have been published previously [7,10]. bProportion of swabs with fusidic acid resistance per number of swabs with S. aureus isolates. cIn 2001 impetigo was registered for the last half year. dYears of epidemic impetigo outbreak [10]. In total, 44 S. aureus isolates from impetigo were subject to molecular analyses, and 11 were found to be related to the EEFIC (Table II). Of the 11 EEFIC isolates from 2008–2009, none showed PFGE identity with the reference strain collected in 2001, but all had closely related PFGE patterns. Eight had identical spa type (t171), while three strains had the closely related spa types of t659 (two isolates) and t645 [7].

o be related to the EEFIC (Table II). Of the 11 EEFIC isolates from 2008–2009, none showed PFGE identity with the reference strain collected in 2001, but all had closely related PFGE patterns. Eight had identical spa type (t171), while three strains had the closely related spa types of t659 (two isolates) and t645 [7]. Table II. Susceptibility testing, spa typing and relatedness to EEFIC in 44 impetigo and 33 non-impetigo Staphylococcus aureus isolates from the years 2008–2012. Year Isolate no. Fusidic acid susceptibility PFGE-relatedness to EEFIC Spa type spa-relatedness to EEFIC Impetigo isolates 2008–09 1–8 R CR t171 ID 9 S CR t645 CR 10–11 R CR t659 CR 12–13 R NR t008 NR 14–28 S NR NA NA 2010–12 29–35 S NA t084 NR 36 S NA t505 NR 37 S NA t726 NR 38 S NA t330 NR 39 R NA t127 NR 40 S NA t160 NR 41 S NA t015 NR 42 S NA t334 NR 43 S NA t094 NR 44 S NA t085 NR Non-impetigo isolates 2008–09 45–55 S NR NA NA 2010–12 56–58 S NA t084 NR 59-61 R NA t127 NR 62 S NA t127 NR 63 S NA t085 NR 64 S NA t026 NR 65 S NA t12271 NR 66 S NA t116 NR 67 S NA t091 NR 68 S NA t279 NR 69 S NA t216 NR 70 S NA t2119 NR 71 S NA t065 NR 72 S NA t136 NR 73 S NA t2133 NR 74 S NA t002 NR CR, closely related; ID, identical; NA, not applicable; NR, not related. Of the 33 non-EEFIC S. aureus isolates from impetigo, 30 (91%) were susceptible to fusidic acid. The EEFIC clone was responsible for 77% (10 of 13) of impetigo S. aureus isolates with resistance to fusidic acid, and 91% (10 of 11) of EEFIC isolates were FAR [7].

Year Isolate no. Fusidic acid susceptibility PFGE-relatedness to EEFIC Spa type spa-relatedness to EEFIC Impetigo isolates 2008–09 1–8 R CR t171 ID 9 S CR t645 CR 10–11 R CR t659 CR 12–13 R NR t008 NR 14–28 S NR NA NA 2010–12 29–35 S NA t084 NR 36 S NA t505 NR 37 S NA t726 NR 38 S NA t330 NR 39 R NA t127 NR 40 S NA t160 NR 41 S NA t015 NR 42 S NA t334 NR 43 S NA t094 NR 44 S NA t085 NR Non-impetigo isolates 2008–09 45–55 S NR NA NA 2010–12 56–58 S NA t084 NR 59-61 R NA t127 NR 62 S NA t127 NR 63 S NA t085 NR 64 S NA t026 NR 65 S NA t12271 NR 66 S NA t116 NR 67 S NA t091 NR 68 S NA t279 NR 69 S NA t216 NR 70 S NA t2119 NR 71 S NA t065 NR 72 S NA t136 NR 73 S NA t2133 NR 74 S NA t002 NR CR, closely related; ID, identical; NA, not applicable; NR, not related. Of the 33 non-EEFIC S. aureus isolates from impetigo, 30 (91%) were susceptible to fusidic acid. The EEFIC clone was responsible for 77% (10 of 13) of impetigo S. aureus isolates with resistance to fusidic acid, and 91% (10 of 11) of EEFIC isolates were FAR [7]. In 2010–2012, no new EEFIC isolates were found. The detailed listing of spa types from both impetigo and non-impetigo specimens from this period is shown in Table II. Two spa types were involved in both impetigo and non-impetigo skin infections; t084 were found in seven impetigo infections and in three non-impetigo infections, and t127 were found in one impetigo infection and in four non-impetigo infections. spa type t127 was responsible for all cases of FAR during the years 2010–2012, both the one impetigo case and three non-impetigo cases. One isolate with spa type t127 was susceptible to fusidic acid.

and in three non-impetigo infections, and t127 were found in one impetigo infection and in four non-impetigo infections. spa type t127 was responsible for all cases of FAR during the years 2010–2012, both the one impetigo case and three non-impetigo cases. One isolate with spa type t127 was susceptible to fusidic acid. Of 11 S. aureus isolates from skin infections other than impetigo during the years 2008–2009 analysed by susceptibility testing and PFGE, all turned out to be fusidic acid susceptible, and none were related to the EEFIC [7]. In the years 2010–2012, 3 of the 19 S. aureus isolates from non-impetigo skin infections were FAR, but none were related to the EEFIC. Discussion In the present study there was a parallel decline in impetigo rate and the proportion of FAR S. aureus isolated from impetigo during the years 2002–2012. No impetigo isolates were FAR in 2011 and 2012. For the years 2008–2012 the vast majority of fusidic acid resistance in S. aureus in impetigo was caused by the EEFIC, making it reasonable to argue that the great predominance of fusidic acid resistance during the years 2002–2007 was also driven by the EEFIC. The data from the present study suggest that, as far as the community of Austevoll is concerned, the epidemic related to the EEFIC has come to an end.

Discussion In the present study there was a parallel decline in impetigo rate and the proportion of FAR S. aureus isolated from impetigo during the years 2002–2012. No impetigo isolates were FAR in 2011 and 2012. For the years 2008–2012 the vast majority of fusidic acid resistance in S. aureus in impetigo was caused by the EEFIC, making it reasonable to argue that the great predominance of fusidic acid resistance during the years 2002–2007 was also driven by the EEFIC. The data from the present study suggest that, as far as the community of Austevoll is concerned, the epidemic related to the EEFIC has come to an end. Whether this conclusion is generalizable to all of Norway, and to all of Northern Europe, is an important question. The EPISA study of antimicrobial susceptibility of S. aureus-related skin and soft tissue infections in general practice in France, the UK and Ireland during 2003–2004 found a high proportion of EEFIC identified in impetigo [5]. In 2012, Dutch researchers investigated the prevalence of the EEFIC in general practice patients with skin or soft tissue infections during 2007 and 2008 [6], and they identified EEFIC in a little over 30% of S. aureus isolates from skin lesions. However, these two studies do not give data about time trends of the EEFIC prevalence.

h researchers investigated the prevalence of the EEFIC in general practice patients with skin or soft tissue infections during 2007 and 2008 [6], and they identified EEFIC in a little over 30% of S. aureus isolates from skin lesions. However, these two studies do not give data about time trends of the EEFIC prevalence. A Swedish follow-up study from the years 1993–2004 investigating the prevalence of S. aureus isolates being resistant to fusidic acid (FAR) in selected nationwide microbiological laboratories, found the proportion of FAR for superficial skin and soft tissue infections in children to decline from a maximum of about 47% in 2002 to 35% in 2004 [13]. Another Swedish study of patients attending a dermatological outpatient clinic for impetigo and infected atopic dermatitis in the years 2004–2008 showed that the proportion of FAR in impetigo and infected atopic dermatitis caused by S. aureus was diminishing simultaneously, with the proportion of FAR in impetigo decreasing from 33% to 24% over the years [8].

ing a dermatological outpatient clinic for impetigo and infected atopic dermatitis in the years 2004–2008 showed that the proportion of FAR in impetigo and infected atopic dermatitis caused by S. aureus was diminishing simultaneously, with the proportion of FAR in impetigo decreasing from 33% to 24% over the years [8]. In 2011, a population-based study from Northern Denmark recorded bacterial data from skin and mucosal membranes of patients with skin infections for the time period of 1997–2008 [9]. They found that the prevalence of S. aureus isolated in impetigo had a marked rise to a maximum in 2002, with a gradual decline thereafter. The proportion of the impetigo S. aureus isolates that were FAR was almost 50% during the years 2003–2006, and diminished after that. In the 2012 report of the Norwegian Antibiotic Resistance Surveillance system [14], national data suggested the fusidic acid resistance to S. aureus in wound isolates to be reduced from a maximum of 25% in 2004 to a stable level of about 10% from the year 2008 on. A study from the UK for the years 1995–2010, which was based on a large primary care diagnosis database, showed national impetigo incidence to double from 1995 to 2001, and to regress to a little below the baseline of 1995 by 2010 [15]. However, neither of these studies provided molecular data. It is likely that these identifiable trends of diminishing prevalence of S. aureus fusidic acid resistance in Sweden, Denmark and Norway, and of impetigo in the UK, indicate a significant attenuation of the presence of EEFIC in these countries.

In 2011, a population-based study from Northern Denmark recorded bacterial data from skin and mucosal membranes of patients with skin infections for the time period of 1997–2008 [9]. They found that the prevalence of S. aureus isolated in impetigo had a marked rise to a maximum in 2002, with a gradual decline thereafter. The proportion of the impetigo S. aureus isolates that were FAR was almost 50% during the years 2003–2006, and diminished after that. In the 2012 report of the Norwegian Antibiotic Resistance Surveillance system [14], national data suggested the fusidic acid resistance to S. aureus in wound isolates to be reduced from a maximum of 25% in 2004 to a stable level of about 10% from the year 2008 on. A study from the UK for the years 1995–2010, which was based on a large primary care diagnosis database, showed national impetigo incidence to double from 1995 to 2001, and to regress to a little below the baseline of 1995 by 2010 [15]. However, neither of these studies provided molecular data. It is likely that these identifiable trends of diminishing prevalence of S. aureus fusidic acid resistance in Sweden, Denmark and Norway, and of impetigo in the UK, indicate a significant attenuation of the presence of EEFIC in these countries. More epidemiological studies of superficial skin infections from different parts of Northern and Central Europe, involving application of molecular analyses of the bacteria, are needed to confirm this conclusion. However, we find the results from the current study sufficient to suggest that the impetigo epidemic related to the EEFIC is most likely near its end.

skin infections from different parts of Northern and Central Europe, involving application of molecular analyses of the bacteria, are needed to confirm this conclusion. However, we find the results from the current study sufficient to suggest that the impetigo epidemic related to the EEFIC is most likely near its end. Another question is to what degree the EEFIC has specifically been the cause of impetigo and not of other skin infections like skin abscesses, paronychiae and other infections of fingers and toes, superinfection of atopic dermatitis, folliculitis, furunculosis and cellulitis. When O’Neill et al first described the EEFIC [4], they found that the clone possesses genes previously known to be linked to impetigo, like exfoliative toxins A and B and EDIN-C. In a previous article analysing our material from the years 2001–2005, we showed an inverse relationship between the proportion of FAR in impetigo and in other superficial skin infections, as the proportion of FAR in impetigo at the time was 76% and for other superficial skin infections it was 18% [10]. Our recent data from 2010–2012 show that a diversity of spa types cause both impetigo and non-impetigo infections. The most common spa type found in impetigo is also frequently identified in non-impetigo skin infections, indicating that the strains of S. aureus that are most prevalent at present do not possess the same specificity for impetigo as the EEFIC did.

diversity of spa types cause both impetigo and non-impetigo infections. The most common spa type found in impetigo is also frequently identified in non-impetigo skin infections, indicating that the strains of S. aureus that are most prevalent at present do not possess the same specificity for impetigo as the EEFIC did. Based on our material, it seems reasonable to maintain that the EEFIC has been specifically inclined to be associated with impetigo, but not with other superficial skin infections. On the contrary, other studies such as the EPISA study [5] and the study by Rijnders et al. from the Netherlands [6], found the EEFIC in other types of skin infections as well as in impetigo. However, these studies do not seem to be based on accurate clinical data. Possibly, their results may have been subject to mixing of cases of impetigo and other skin infections, thus not being able to identify the high degree of impetigo specificity in EEFIC. The present study is based on cases with strict clinical diagnosis as an inclusion criterion.

m to be based on accurate clinical data. Possibly, their results may have been subject to mixing of cases of impetigo and other skin infections, thus not being able to identify the high degree of impetigo specificity in EEFIC. The present study is based on cases with strict clinical diagnosis as an inclusion criterion. The strengths of our study are the exact number of the total population under study, the clinical definition of the cases to be included as impetigo patients, the reliable identification of all impetigo patients and the uniform registration over a long timespan. Weaknesses of the study are that we do not have molecular analyses for the first 6 years, that the molecular methods were not uniformly performed in the periods 2008–2009 and 2010–2012, and that the number of patients in recent years has been small, thus reducing the generalizability of the conclusions. The steady decline over the years of S. aureus fusidic acid resistance in impetigo and the consistent absence of EEFIC during the last 3 years are strong indications of the extinction of this epidemic in our community. Acknowledgments We thank Lillian Marstein, Department of Medical Microbiology, St Olav’s University Hospital, who performed the spa typing analyses, and the GPs of Austevoll who diagnosed and treated the patients in this study. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Acknowledgments We thank Lillian Marstein, Department of Medical Microbiology, St Olav’s University Hospital, who performed the spa typing analyses, and the GPs of Austevoll who diagnosed and treated the patients in this study. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. This work was supported by the Foundation for Research in General Practice (grant no. 07/698), and the Norwegian Surveillance System for Antimicrobial Resistance (grant no. 22.12.2008).

Introduction Early diagnosis of HIV is important for the prognosis of individual patients, because antiretroviral treatment (ART) can be started at the appropriate time, as well as for public health, since transmission can be prevented [1]. In the early years of the 21st century, several studies were published in Europe investigating the trend in late diagnosis [2]. The objective of these studies was to investigate whether the introduction of more effective ART had decreased the time from infection to diagnosis. Surprisingly, most studies found a stable or increasing trend of late diagnosis. The ‘late presenters’ were found mainly among immigrants or in population groups considered to have a low risk of HIV infection or who were not covered by routine screening, such as people above 40 years of age, heterosexuals, men (compared to women), and those having children [2]. Newer studies on late presentation or diagnosis are scarce and the reported percentages of late presenters among newly diagnosed HIV patients in Europe vary considerably (from 12% to 60%) [1].

routine screening, such as people above 40 years of age, heterosexuals, men (compared to women), and those having children [2]. Newer studies on late presentation or diagnosis are scarce and the reported percentages of late presenters among newly diagnosed HIV patients in Europe vary considerably (from 12% to 60%) [1]. The definitions for late diagnosis have varied widely between studies. Some studies used laboratory-based definitions, such as CD4 + T-lymphocyte (CD4) counts below 200 or 350 cells/μl at the time of diagnosis, whereas other studies used clinical definitions based on time to development of AIDS [2,3]. Unfortunately, none of these definitions are linearly related to time from infection, but rather a measure of disease progression at time of diagnosis in relation to the optimal time for start of ART [4,5]. A related approach to explore the epidemiology of the disease is to estimate HIV incidence in populations using serological assays [6], such as the BED assay (HIV-1 IgG capture BED enzyme-linked immunoassay). These assays detect recent infections among all HIV-positive cases; where recent infection means seroconversion within approximately the previous 6 months. A major advantage of this method is that it provides information regarding current HIV transmission and testing, rather than late presentation. The BED assay was developed by the Centers for Disease Control and Prevention (CDC) in Atlanta, USA and measures the levels of HIV-1-specific antibodies out of total IgG, which increases with time since infection [7]. However, the BED assay can give false-positive recent results, e.g. for patients with low CD4 counts [8,9]. Thus, removing patients with low CD4 count from those classified as having recent infections was recommended by UNAIDS [10]. To further increase the specificity of the result from the BED assay a recent infection testing algorithm (RITA), taking CD4 counts as well as clinical information into account, was developed by the European Centre for Disease Prevention and Control (ECDC) [11] and used in testing algorithms in, for example, the United Kingdom [12].

rease the specificity of the result from the BED assay a recent infection testing algorithm (RITA), taking CD4 counts as well as clinical information into account, was developed by the European Centre for Disease Prevention and Control (ECDC) [11] and used in testing algorithms in, for example, the United Kingdom [12]. To allow for international comparability, we used the algorithm proposed by the ECDC in the present surveillance study on HIV patients diagnosed in Sweden between 2003 and 2010. Patients classified as having recent infection were compared to patients with delayed diagnosis to investigate whether there were trends in early HIV diagnosis over recent years and to identify factors associated with early diagnosis. In order to detect changes over time in HIV testing behavior due to prevention efforts within the national strategy for HIV prevention in Sweden [13], the study was restricted to people who should have been reached by these efforts, i.e. we did not include immigrants infected abroad.

rs associated with early diagnosis. In order to detect changes over time in HIV testing behavior due to prevention efforts within the national strategy for HIV prevention in Sweden [13], the study was restricted to people who should have been reached by these efforts, i.e. we did not include immigrants infected abroad. Materials and methods Data collection and inclusion criteria We used clinical, epidemiological, and laboratory data as well as plasma samples from a previously published study, which investigated transmitted drug resistance among 1463 HIV patients who were diagnosed in Sweden during 2003–2010 [14]. The previous study included approximately 44% of all newly diagnosed patients who had been reported as HIV-1-infected in the national Swedish surveillance system (www.sminet.se) during the study period and was reasonably well matched to them, except for a slight over-representation of men who have sex with men (MSM).

. The previous study included approximately 44% of all newly diagnosed patients who had been reported as HIV-1-infected in the national Swedish surveillance system (www.sminet.se) during the study period and was reasonably well matched to them, except for a slight over-representation of men who have sex with men (MSM). Informed written or oral consent was obtained from all adult participants and from the next of kin, caregivers or guardians on behalf of minors and children and was documented in the patient’s records. The research was conducted according to the Declaration of Helsinki and was approved by the Regional Medical Ethics Board in Stockholm, Sweden (Dnr 02–367, 04–797, 2007/1533, and 2011/1854) which permitted use of either written or oral consent to minimize the risk of selection biases due to patient drop-out due to willingness to take part in the study, but reluctance to provide written consent. All data were anonymized [14]. The study protocol, questionnaire, and database, as well as a system for data verification, were developed as part of a pan- European study of transmitted drug resistance [15]. In the present study we included study subjects from the previous study if they: (i) were reported to have been infected in Sweden or were born in Sweden and reported to have been infected abroad; (ii) had a successful BED result from a sample collected within 120 days from the date of diagnosis; (iii) had a CD4 count available from 120 days before to 120 days after the date of sampling for BED testing.

ere reported to have been infected in Sweden or were born in Sweden and reported to have been infected abroad; (ii) had a successful BED result from a sample collected within 120 days from the date of diagnosis; (iii) had a CD4 count available from 120 days before to 120 days after the date of sampling for BED testing. Data on country of origin, probable country of infection, and transmission route were collected in standardized questionnaires filled out by the patient’s doctor or nurse and were obtained as part of mandatory contact tracing [14]. Laboratory methods The BED assay (Calypte Biomedical Corp, Lake Oswega, OR, USA) was performed according to the manufacturer’s instructions with the recommended cut-off for recent infection of OD-n < 0.8. As mentioned, this cut-off corresponds to approximately 6 months between infection and sampling for BED testing [7]. Data on CD4 counts at diagnosis were available from the previous study [14] and most data on BED test results were available from a separate recent study [16].

cut-off for recent infection of OD-n < 0.8. As mentioned, this cut-off corresponds to approximately 6 months between infection and sampling for BED testing [7]. Data on CD4 counts at diagnosis were available from the previous study [14] and most data on BED test results were available from a separate recent study [16]. Definition of early diagnosis and statistical methods Patients were classified as having early or delayed diagnosis using the ECDC recent infection testing algorithm [11] with one minor modification. Thus, patients were classified as having an early diagnosis if they had a BED OD value < 0.8 in a blood sample drawn within 4 months from diagnosis provided that they did not have low CD4 count (< 200 cells/μl), low viral load (< 400 copies/ml), ongoing ART, and/or an AIDS-defining illness at diagnosis. The last criterion differs from the ECDC RITA, which specifies that patients with AIDS within 1 year of diagnosis should not be classified as recently infected. This modification was used because we had information about AIDS at diagnosis, but not during follow-up. Patients fulfilling the criteria for early diagnosis were compared with remaining patients, who were defined as having delayed diagnosis.

IDS within 1 year of diagnosis should not be classified as recently infected. This modification was used because we had information about AIDS at diagnosis, but not during follow-up. Patients fulfilling the criteria for early diagnosis were compared with remaining patients, who were defined as having delayed diagnosis. We performed a trend analysis using a logistic regression model with early diagnosis as dependent variable and year as the only independent variable. Trend analyses were also done separately for each major transmission group and by country of infection (Sweden vs abroad). We investigated the following factors for association with early diagnosis: age, gender, transmission route, country of infection, and country of birth. Factors identified in univariate logistic regression analysis at a significance level of 5% were included in a multivariable model. All factors were treated as categorical variables. Patients with missing data on country of infection (n = 37) and country of birth (n = 3) were included in the abroad category in the logistic regression. Results The present study included 767 HIV-1-infected patients. Of 1463 patients in the previous study, 609 were excluded as they were reported as both born and infected abroad. An additional 87 patients were excluded due to lack of BED or CD4 test results fulfilling the inclusion criteria (n = 78 and n = 9, respectively).

lts The present study included 767 HIV-1-infected patients. Of 1463 patients in the previous study, 609 were excluded as they were reported as both born and infected abroad. An additional 87 patients were excluded due to lack of BED or CD4 test results fulfilling the inclusion criteria (n = 78 and n = 9, respectively). Table I shows the main characteristics of the study subjects. The three main transmission groups were: men who have sex with men (MSM) (n = 402), heterosexuals (n = 191), and injecting drug users (IDUs) (n = 121). A majority of the study subjects were infected in Sweden (n = 576, 75%). However, it should be stressed that we did not investigate immigrants infected abroad, who constituted around half of all diagnosed patients during the study period. Table I. Factors associated with obtaining an early diagnosis among 767 patients diagnosed with HIV infection in Sweden, 2003–2010.

Table I shows the main characteristics of the study subjects. The three main transmission groups were: men who have sex with men (MSM) (n = 402), heterosexuals (n = 191), and injecting drug users (IDUs) (n = 121). A majority of the study subjects were infected in Sweden (n = 576, 75%). However, it should be stressed that we did not investigate immigrants infected abroad, who constituted around half of all diagnosed patients during the study period. Table I. Factors associated with obtaining an early diagnosis among 767 patients diagnosed with HIV infection in Sweden, 2003–2010. Patients, n (%) Univariate analysis Multivariable analysis Factor Total With early diagnosis OR p value OR p value Transmission route MSM 402 182 (45) (ref) (ref) Heterosexual 191 41 (21) 0.330 < 0.001 0.356 < 0.001 Injecting drug use 121 33 (27) 0.453 0.001 0.459 0.001 Other 53 15 (28) 0.477 0.021 0.490 0.044 Country of infection Sweden 576 218 (38) (ref) (ref) Abroad or unknown 191 53 (28) 0.631 0.012 0.857 0.449 Gender Men 652 240 (37) (ref) (ref) Women 115 31 (27) 0.634 0.043 0.963 0.893 Age group < 25 years 40 22 (55) (ref) (ref) 25–34 years 180 83 (46) 0.700 0.310 0.552 0.113 35–44 years 263 87 (33) 0.404 0.008 0.325 0.002 45–54 years 180 53 (29) 0.341 0.003 0.313 0.002 55–64 years 82 21 (26) 0.282 0.002 0.280 0.003 ≥ 65 years 22 5 (23) 0.241 0.018 0.242 0.024 Country of birth Sweden 593 211 (36) (ref) Abroad or unknown 174 60 (34) 0.953 0.790 MSM, men who have sex with men; OR, odds ratio.

35–44 years 263 87 (33) 0.404 0.008 0.325 0.002 45–54 years 180 53 (29) 0.341 0.003 0.313 0.002 55–64 years 82 21 (26) 0.282 0.002 0.280 0.003 ≥ 65 years 22 5 (23) 0.241 0.018 0.242 0.024 Country of birth Sweden 593 211 (36) (ref) Abroad or unknown 174 60 (34) 0.953 0.790 MSM, men who have sex with men; OR, odds ratio. A total of 271 patients (35%) were diagnosed early according to our definition. The yearly percentage of patients with early diagnosis varied between 24% (year 2003) and 48% (year 2005), but there was no significant time trend (p = 0.836) (Figure 1). Similarly, no significant time trend was found in any of three transmission groups (heterosexuals, p = 0.064; MSM, p = 0.536; or IDUs, p = 0.230) (Figure 1) or by country of infection (Sweden, p = 0.665 or abroad, p = 0.132) (not shown). Early diagnosis was significantly more common among MSM (45%) than among heterosexuals (21%) and IDUs (27%) (p < 0.001 and p = 0.001, respectively). This difference remained in the multivariable analysis (Table I). In the univariate analysis we also found that women were less likely than men to have an early diagnosis (odds ratio 0.63, p = 0.043). This association was no longer significant in the multivariable analysis that adjusted for transmission route and was entirely explained by the difference in time to diagnosis between the heterosexually infected group and MSM (Table I). Similarly, there was a difference in the univariate analysis between persons infected in Sweden or abroad, which disappeared in the multivariable analysis. This was explained by a higher proportion of heterosexual transmission in the group infected abroad compared with the predominance of MSM transmission in Sweden. The factors that remained significantly associated with early diagnosis in the multivariable analysis were young age group and being MSM (Table I).

analysis. This was explained by a higher proportion of heterosexual transmission in the group infected abroad compared with the predominance of MSM transmission in Sweden. The factors that remained significantly associated with early diagnosis in the multivariable analysis were young age group and being MSM (Table I). Figure 1. Percentage of patients with an early HIV diagnosis. The early diagnosis among 767 patients diagnosed with HIV infection in Sweden, 2003–2010, and included in the study, by transmission route.

analysis. This was explained by a higher proportion of heterosexual transmission in the group infected abroad compared with the predominance of MSM transmission in Sweden. The factors that remained significantly associated with early diagnosis in the multivariable analysis were young age group and being MSM (Table I). Figure 1. Percentage of patients with an early HIV diagnosis. The early diagnosis among 767 patients diagnosed with HIV infection in Sweden, 2003–2010, and included in the study, by transmission route. Discussion In this surveillance study we investigated trends in early diagnosis among HIV patients diagnosed in Sweden over the time period 2003–2010 to detect possible changes in HIV testing behavior due to national prevention efforts. The study was restricted to patients reported as infected in Sweden and patients born in Sweden and infected abroad. Immigrants infected abroad were not included, as further discussed below. Our results indicated that about one-third of study patients received their diagnosis within 6 months of infection. Thus, a majority of HIV patients were diagnosed at an undefined time later in the course of the disease. This underlines the fact that delayed HIV diagnosis is a considerable problem in Sweden, as it is internationally [1]. Furthermore, this problem does not appear to diminish over time. For some patients the delayed HIV diagnosis will affect the prognosis because treatment cannot be started at an optimal time [1–19]. Delayed diagnosis is also likely to affect public health because the risk of onward transmission is higher from persons who are unaware of their infection as compared with persons who have been diagnosed [20]. In addition, a majority of diagnosed HIV-1 patients in Sweden receive successful ART [21,22], which greatly reduces infectivity [23].

so likely to affect public health because the risk of onward transmission is higher from persons who are unaware of their infection as compared with persons who have been diagnosed [20]. In addition, a majority of diagnosed HIV-1 patients in Sweden receive successful ART [21,22], which greatly reduces infectivity [23]. The number of patients in each group and each year was small, leading to estimates fluctuating between years and limited statistical power to detect small changes in the trends over the time period. However, this is due to the low incidence of HIV in Sweden. Our study included approximately half of all eligible patients in Sweden during the study period. The total number of notified newly diagnosed HIV cases in Sweden who would have been eligible for the study fluctuated over the years of the study period, with a slight upward trend (4% per year, p < 0.001). There was an HIV outbreak among IDUs in Stockholm in the autumn of 2006, which resulted in an increased number of reported cases in 2007 [24]. However, a majority were not diagnosed early according to our definition and thus were reflected in the dip in early diagnosis among IDUs in 2007.

rend (4% per year, p < 0.001). There was an HIV outbreak among IDUs in Stockholm in the autumn of 2006, which resulted in an increased number of reported cases in 2007 [24]. However, a majority were not diagnosed early according to our definition and thus were reflected in the dip in early diagnosis among IDUs in 2007. A strength of our study is that patients were defined as having an early diagnosis according to the algorithm proposed by the ECDC, which is based on a composite measure of two laboratory tests, i.e. the BED test and CD4 count, as well as clinical information. This should reduce, albeit not eliminate, the risk of misclassification of early infection when the BED assay is used alone. However, we cannot exclude the possibility that individual patients might still have been misclassified. Studies in other European countries, including the UK, France, and Germany, have also documented that many patients have delayed diagnosis [12,25,26]. In our study the percentage of patients with early diagnosis was slightly higher than in these latter might be due to the exclusion of persons born and infected abroad. Our rationale for excluding this group in the study was to avoid trends in immigration affecting our results. To investigate trends in early and delayed diagnosis in this group, data on date of immigration and knowledge of whether the diagnosis was known at the time of immigration are needed, which was not the case for our study population. In an ongoing study in Sweden, immigrants have been identified as having the highest proportion of late presenters (CD4 < 350) [27].

agnosis in this group, data on date of immigration and knowledge of whether the diagnosis was known at the time of immigration are needed, which was not the case for our study population. In an ongoing study in Sweden, immigrants have been identified as having the highest proportion of late presenters (CD4 < 350) [27]. In the present study the MSM group had the highest percentage of early diagnosis, concordant with studies which show that testing coverage and frequency is higher in this group than in other groups [22]. Nonetheless, a majority of MSM and IDUs were estimated to have been diagnosed more than 6 months after infection, despite both groups being recognized as having an increased risk of HIV infection. Therefore, the present study shows that there is room for improvements in secondary prevention efforts in these, as well as in other, transmission groups. As we did not investigate reasons behind delayed diagnosis, additional in-depth studies are needed to guide improvements in prevention strategies, including investigation of whether there is mainly patient’s or doctor’s delay. Although delayed diagnosis is of concern, recent infection implies ongoing HIV transmission. Our results indicate that this occurred among MSM, IDUs, and other groups in Sweden, emphasizing that primary prevention strategies also need to be strengthened and directed to groups and individuals at high risk of contracting HIV.

ugh delayed diagnosis is of concern, recent infection implies ongoing HIV transmission. Our results indicate that this occurred among MSM, IDUs, and other groups in Sweden, emphasizing that primary prevention strategies also need to be strengthened and directed to groups and individuals at high risk of contracting HIV. Acknowledgments Thanks to Rigmor Thorstensson, Hans Gaines, Monica Ideström, Kajsa Aperia, Frida Hansdotter, Maria Axelsson, Gunilla Rådö, and Susanne Karregård at the Public Health Agency of Sweden and Eva C. Eriksson at Karolinska University Hospital. The research leading to these results has received funding from the Swedish Research Council (grant nos K2008-56X-09935-17-3 and K2001-35 56X-0095-20-6); from the Swedish International Development Cooperation Agency (grant no. SWE-2006-018); and the EU projects: SPREAD (QLK2-CT-2001-37 01344); EHR (LSHP-CT-2006–518211); CHAIN (FP7/2007–2013) ‘Collaborative HIV and Anti-HIV Drug Resistance Network,’ and FP7 grant agreement no. 223131 under EuroCoord grant agreement no. 260694. H.S. was supported by a postdoctoral fellowship from the Swedish Research Council (623-2011-1100, 623-2013-8905). Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Introduction In 2008 the Swiss AIDS Commission announced that people infected with HIV who are on effective antiretroviral therapy (ART) should not be considered infectious through sexual contact, provided that certain criteria are fulfilled [1]. This drew considerable attention to the scientific evidence for the transmission risk from patients on ART. The subject became topical again in 2011 with the release of the results from the HPTN 052 study [2]. This study followed 1763 serodiscordant couples where one partner was HIV-positive and the other HIV-negative at the beginning of the study. The couples were enrolled from 2007 to 2010 and randomized into 2 study groups, one in which the HIV-positive partner immediately received ART irrespective of their immune status, and a second where ART was started later if an indication for treatment developed (i.e. CD4 count < 250 cells/μl blood). All participants received advice about the use of condoms. The study demonstrated that early ART was associated with a 96% reduction in the risk of transmission through sexual contact compared with ART started later. This confirmed the results of several previous observational studies. These findings have led to extensive scientific discussions about how ART might be used in the prevention of HIV transmission (so-called treatment as prevention, TasP).

the risk of transmission through sexual contact compared with ART started later. This confirmed the results of several previous observational studies. These findings have led to extensive scientific discussions about how ART might be used in the prevention of HIV transmission (so-called treatment as prevention, TasP). Against a background of recent scientific discoveries and the ongoing discourse, several national expert groups, in addition to the Swiss, have published their opinions. In the United Kingdom, the British HIV Association (BHIVA) and the Expert Advisory Group on AIDS (EAGA) have stated that there is an extremely low risk of transmission through sexual contact from people who are continuously fully suppressed on ART, provided that no other sexually transmitted infections are present [3]. There is also a parallel discussion into the possibility of preventing HIV spread through the large-scale use of post-exposure prophylaxis (PEP) and pre-exposure prophylaxis (PrEP). PEP describes the initiation of ART immediately following a single HIV exposure with the aim of preventing transmission, whereas PrEP involves the preventative treatment of HIV-negative people who have an ongoing or recurrent risk of infection.

use of post-exposure prophylaxis (PEP) and pre-exposure prophylaxis (PrEP). PEP describes the initiation of ART immediately following a single HIV exposure with the aim of preventing transmission, whereas PrEP involves the preventative treatment of HIV-negative people who have an ongoing or recurrent risk of infection. The Swedish national quality registry InfCare HIV includes more than 99% of all known HIV cases in Sweden. According to the registry, 87% of all HIV-positive patients in Sweden were receiving ART in 2012 (http://infcare.com/hiv/sv/resultat/2012-arsrapport/, in Swedish). Of these, 92% had effective ART, i.e. a plasma viral load < 50 HIV RNA copies/ml. In light of this and the findings of the HPTN 052 study, there is great demand for comprehensive information about the most current evidence on the risk of transmission from patients who are on effective ART. There is also a need for knowledge about the risk of HIV transmission from those who are not on ART and about the long-term medical consequences for people living with HIV infection.

demand for comprehensive information about the most current evidence on the risk of transmission from patients who are on effective ART. There is also a need for knowledge about the risk of HIV transmission from those who are not on ART and about the long-term medical consequences for people living with HIV infection. This position statement from the Public Health Agency of Sweden and Swedish Reference Group for Antiviral Therapy is based on a workshop organized in the fall of 2012. It summarizes the latest research and knowledge on the risk of HIV transmission from patients on ART, with a focus on the risk of sexual transmission. The risk of transmission via shared injection equipment among intravenous drug users is also examined, as is the risk of mother-to-child transmission. The text was published online in Swedish on the website of the Public Health Agency of Sweden in October 2013, together with 9 background articles (also in Swedish). Medical consequences of HIV infection HIV infection is still a serious, incurable disease that requires lifelong treatment. The life-expectancy of people infected with HIV in industrialized countries has increased markedly and is becoming comparable to that of uninfected people. In Sweden, HIV infection now very seldom leads to death if the infection is diagnosed in time to start ART before any serious immunodeficiency has developed.

Medical consequences of HIV infection HIV infection is still a serious, incurable disease that requires lifelong treatment. The life-expectancy of people infected with HIV in industrialized countries has increased markedly and is becoming comparable to that of uninfected people. In Sweden, HIV infection now very seldom leads to death if the infection is diagnosed in time to start ART before any serious immunodeficiency has developed. Modern ART was introduced in 1996 and quickly led to a dramatic reduction in both the morbidity and mortality caused by HIV infection. Further improvements have since been made, both in antiviral effect and reduction in adverse effects, with positive implications for the patient’s experience of ART and the impact on health-related quality of life [4].

and quickly led to a dramatic reduction in both the morbidity and mortality caused by HIV infection. Further improvements have since been made, both in antiviral effect and reduction in adverse effects, with positive implications for the patient’s experience of ART and the impact on health-related quality of life [4]. Resistance to the antiretroviral drugs may develop, but, with few exceptions, this can be managed by exchanging all or some of the drugs. Several studies have shown that the life-expectancy of HIV patients in industrialized countries is increasing and is now close to that of the rest of the population [5–7]. An important reason for the remaining shortened life-expectancy is that, aside from factors connected to lifestyle and socio-economic status, some patients are diagnosed at such a late stage that ART cannot be started in time to have an effect [8]. Data from InfCare HIV show that all-cause mortality among HIV patients in Sweden is currently lower than 1% annually (http://infcare.com/hiv/sv/resultat/2012-arsrapport/, in Swedish). However, the mortality is significantly higher among those diagnosed late in disease progression, i.e. with serious immunodeficiency, and those who were infected through intravenous drug use. Definition of effective antiretroviral therapy The following criteria must be fulfilled in order for the antiretroviral therapy of HIV infection to be considered effective: The viral load of HIV RNA in the blood plasma must be continuously < 50 copies/ml, verified in 2 successive measurements conducted at an interval of 3–6 months.

Definition of effective antiretroviral therapy The following criteria must be fulfilled in order for the antiretroviral therapy of HIV infection to be considered effective: The viral load of HIV RNA in the blood plasma must be continuously < 50 copies/ml, verified in 2 successive measurements conducted at an interval of 3–6 months. The patient must maintain a continuously high adherence to treatment. Monitoring of viral load and adherence to treatment must take place regularly in accordance with Referensgruppen för Antiviral Terapi (RAV) guidelines, i.e. 2–4 times per y [9]. In addition, there must not be any clinical or epidemiological reason to suspect the presence of any other ongoing sexually transmitted infection, as this theoretically could increase the risk of transmission even if ART is effective.

Monitoring of viral load and adherence to treatment must take place regularly in accordance with Referensgruppen för Antiviral Terapi (RAV) guidelines, i.e. 2–4 times per y [9]. In addition, there must not be any clinical or epidemiological reason to suspect the presence of any other ongoing sexually transmitted infection, as this theoretically could increase the risk of transmission even if ART is effective. Low yet detectable plasma viral loads of up to 500 copies/ml are seen in a limited number of patients with good adherence to treatment and effective ART. When viral loads up to this level are detected on any single occasion, they are referred to as ‘blips’. The causes of these blips may be both biological and related to the measurement technique, but they are not usually an indication of increased viral replication. Blips are seen in a majority of patients with effective ART if the viral load is measured sufficiently often. This also applies to the patients who were involved in the HPTN 052 study and other studies that form the basis for the assessment of the risk of HIV transmission during ART. There is no indication that patients receiving effective therapy who have blips are more infectious than patients without documented blips. A small proportion of patients on ART instead have continuously identifiable low-level viraemia, i.e. a low presence of virus in plasma (50–500 copies/ml). There are not yet sufficient data to assess with complete certainty the transmission risk from these patients, but available data indicate that it is very low [10].

A small proportion of patients on ART instead have continuously identifiable low-level viraemia, i.e. a low presence of virus in plasma (50–500 copies/ml). There are not yet sufficient data to assess with complete certainty the transmission risk from these patients, but available data indicate that it is very low [10]. Assessment of the risk of transmission through sexual contact The risks of transmission through vaginal and anal intercourse in cases of effective ART are as follows: There is minimal risk of transmission through vaginal and anal intercourse if the HIV-infected partner is on effective ART and a condom is used throughout intercourse. There is also a very low risk of transmission through vaginal and anal intercourse if the HIV-infected partner is on effective ART and a condom is not used. The above applies for each individual sexual contact and in cases of repeated contact over the course of longer periods (y), regardless of whether the HIV-infected partner is a woman or a man and regardless of whether the HIV-infected partner is penetrative or receptive during the sexual act. With regard to the risk of transmission through vaginal intercourse, the assessment above is supported primarily by the prospective HPTN 052 study [2], but also by several observational studies. A recently published meta-analysis of the results from 6 different studies covering a total of 6070 heterosexual serodiscordant couples where the HIV-positive partner had effective ART calculated the risk of transmission to be < 0.01 per 100 person-y [11].

HPTN 052 study [2], but also by several observational studies. A recently published meta-analysis of the results from 6 different studies covering a total of 6070 heterosexual serodiscordant couples where the HIV-positive partner had effective ART calculated the risk of transmission to be < 0.01 per 100 person-y [11]. In the treatment group of the HPTN 052 study there was 1 transmission observed in approximately 1500 person-y, which corresponds to a risk of transmission of approximately 1 per 150,000 sexual contacts. Furthermore, it has been reported that this single observed transmission took place before or very soon after the HIV-infected partner had initiated ART. This means that the available data do not contradict the Swiss statement that there may be a non-existent (zero) risk of transmission through vaginal intercourse when a patient is on effective ART. However, zero risk is impossible to demonstrate scientifically. It is probable that the risk of transmission is also minimal in cases of effective ART even when a condom is not used. However, because condom use was encouraged in the HPTN 052 study, there is insufficient scientific evidence currently available to support such a conclusion. In addition, condoms are recommended because the risk of transmission of other sexually transmitted infections may be present in the absence of symptoms. There is a lack of knowledge about the potential of other barrier methods to reduce the risk of transmission.

idence currently available to support such a conclusion. In addition, condoms are recommended because the risk of transmission of other sexually transmitted infections may be present in the absence of symptoms. There is a lack of knowledge about the potential of other barrier methods to reduce the risk of transmission. Furthermore, the risk of transmission is assessed to be very low even if treatment does not entirely comply with the above criteria of effective ART. This is based on the reduction in the risk of transmission of at least 96% seen in the HPTN 052 study, even though effective ART was defined as a viral load < 1000 copies/ml, rather than < 50 copies/ml. Furthermore, 5% of patients in the HPTN 052 study had virus levels > 1000 copies/ml. This conclusion is also supported by a meta-analysis of the results from several studies, covering a total of 5021 heterosexual couples and 461 transmission events, in which there were no transmissions observed from patients with a viral load below 400 copies/ml [10].

e HPTN 052 study had virus levels > 1000 copies/ml. This conclusion is also supported by a meta-analysis of the results from several studies, covering a total of 5021 heterosexual couples and 461 transmission events, in which there were no transmissions observed from patients with a viral load below 400 copies/ml [10]. There are no prospective studies that directly address the risk of transmission through unprotected anal intercourse from patients on effective ART. The assessment above is thus extrapolated from risks that are better understood. For example, in cases of untreated HIV infection the risk of transmission per sexual contact is on average about 10 times higher for the receptive partner in anal intercourse than in vaginal intercourse. The risk of transmission is lower for the penetrative partner than for the receptive partner. It is likely that effective ART reduces the risk of transmission through anal intercourse to about the same degree as through vaginal intercourse. This was also the conclusion recently drawn by an expert committee from the World Health Organization (WHO) [12]. There has only been 1 case described in the literature in which transmission has taken place between 2 men despite the HIV-infected partner being on effective ART [13]. The absence of similar cases in the international medical literature indicates that transmission through vaginal or anal intercourse from patients on effective ART is highly unusual, as such cases would be of great academic, epidemiological, and clinical interest. Furthermore, there have been no known cases in Sweden of sexual transmission from patients who meet the criteria for effective ART.

es that transmission through vaginal or anal intercourse from patients on effective ART is highly unusual, as such cases would be of great academic, epidemiological, and clinical interest. Furthermore, there have been no known cases in Sweden of sexual transmission from patients who meet the criteria for effective ART. Risk of transmission through oral sexual contact in cases of effective ART The risk of transmission through oral sexual contact is assessed to be minimal if the HIV-infected partner is on effective ART. This applies regardless of gender or type of sexual contact (heterosexual or homosexual). There are no studies on the risk of transmission through oral sexual contact where the HIV-infected partner is on effective ART. However, in cases of untreated HIV infection, the risk of transmission through oral sexual contact is lower than through vaginal intercourse, which provides support for the assessment above. The significance of HIV RNA in genital secretions in cases of effective ART Low levels of HIV RNA are sometimes detected in the genital secretions of patients on effective ART. However, this has not been shown to be of significance to the risk of transmission.

There are no studies on the risk of transmission through oral sexual contact where the HIV-infected partner is on effective ART. However, in cases of untreated HIV infection, the risk of transmission through oral sexual contact is lower than through vaginal intercourse, which provides support for the assessment above. The significance of HIV RNA in genital secretions in cases of effective ART Low levels of HIV RNA are sometimes detected in the genital secretions of patients on effective ART. However, this has not been shown to be of significance to the risk of transmission. Several studies have reported findings of low, yet detectable, levels of HIV RNA in the semen and cervical secretions of ART-treated patients who do not have detectable levels of HIV RNA in their blood plasma [14,15]. However, it has not been established whether these patients are contagious. Cohen and colleagues maintain that low levels of HIV RNA in genital secretions are unlikely to significantly affect contagiousness, arguing that some participants in the HPTN 052 study and observational studies probably also had low levels of HIV RNA in their genital secretions, but ART was still associated with a dramatically reduced risk of transmission [16]. Assessment of the risk of transmission from intravenous drug users on effective ART Based on the available indirect data, the risk of HIV transmission between intravenous drug users is thought to be markedly reduced if the HIV-infected person is on effective ART.

Several studies have reported findings of low, yet detectable, levels of HIV RNA in the semen and cervical secretions of ART-treated patients who do not have detectable levels of HIV RNA in their blood plasma [14,15]. However, it has not been established whether these patients are contagious. Cohen and colleagues maintain that low levels of HIV RNA in genital secretions are unlikely to significantly affect contagiousness, arguing that some participants in the HPTN 052 study and observational studies probably also had low levels of HIV RNA in their genital secretions, but ART was still associated with a dramatically reduced risk of transmission [16]. Assessment of the risk of transmission from intravenous drug users on effective ART Based on the available indirect data, the risk of HIV transmission between intravenous drug users is thought to be markedly reduced if the HIV-infected person is on effective ART. There are no studies that provide a direct answer regarding the risk of transmission via injection equipment that is shared between intravenous drug users when the HIV-infected person is on effective ART. However, 2 observational studies from British Columbia, Canada and Baltimore, USA, indicate that reduced viral load at the population level, as a result of the increased use of ART, is associated with a reduced incidence of HIV infections among intravenous drug users [17,18]. Based on these findings, Wood and colleagues recently concluded that ART is also relevant to the prevention of HIV transmission via shared needles [19]. The risk of transmission of other blood-borne infections such as hepatitis C remains unchanged, even in cases of successful HIV treatment.

ravenous drug users [17,18]. Based on these findings, Wood and colleagues recently concluded that ART is also relevant to the prevention of HIV transmission via shared needles [19]. The risk of transmission of other blood-borne infections such as hepatitis C remains unchanged, even in cases of successful HIV treatment. In summary, it is highly probable that the risk of blood-borne transmission of HIV between intravenous drug users is significantly reduced if the HIV-infected person is on effective ART, but the magnitude of the reduction is still unclear. Assessment of the risk of mother-to-child HIV transmission during pregnancy and childbirth The risk of HIV transmission from mother to child is less than 0.5% if the pregnant woman has effective ART beginning well in advance of delivery [20]. The very low risk of mother-to-child transmission and recent advances in HIV treatment that have extended life-expectancy and improved quality of life have meant that more HIV-infected women are planning to have children. Although reduced fertility is probably more common among HIV-infected women, they are not currently offered in vitro fertilization (IVF) in Sweden, in accordance with regulations governing the donation and utilization of organs, tissues, and cells. The opportunity for IVF is now available to HIV-positive women in Denmark and several other countries inside and outside of the European Union. Acknowledgements Dr John Litell, Beth Israel Deaconess Medical Center, Boston, USA has generously reviewed and improved the translation of the document into English.

Although reduced fertility is probably more common among HIV-infected women, they are not currently offered in vitro fertilization (IVF) in Sweden, in accordance with regulations governing the donation and utilization of organs, tissues, and cells. The opportunity for IVF is now available to HIV-positive women in Denmark and several other countries inside and outside of the European Union. Acknowledgements Dr John Litell, Beth Israel Deaconess Medical Center, Boston, USA has generously reviewed and improved the translation of the document into English. Declaration of interest The authors report no conflicts of interest relevant to this work. The authors alone are responsible for the content and writing of the paper.