Herpes simplex virus type 2 infection as a biomarker for sexual debut among young people in sub-Saharan Africa: a literature review

Abstract

Biological markers are needed in order to provide objective measures to validate self-reported sexual behaviour and interpret prevention trial data. In this review, we evaluated herpes simplex type 2 virus (HSV-2), one of the most prevalent sexually transmitted infections in sub-Saharan Africa as a biological marker of sexual debut. Based on our findings, we do not recommend using HSV-2 as a biomarker for sexual debut due to its low transmission probabilities and the fact that HSV-2 prevalence is not 100% among potential sexual partners. We recommend that the validation of alternative biological measures should be prioritized, and included in future studies and trials of interventions to reduce sexual health risk.

Keywords

sexually transmitted infections STI herpes simplex type 2 HSV-2 seroprevalence genital herpes biological marker sexual debut Africa

INTRODUCTION

Young people living in sub-Saharan Africa (SSA) are consistently identified as one of the most important groups for sexual and reproductive health programmes to prevent unwanted pregnancies, HIV and other sexually transmitted infections (STIs).¹ In the absence of a vaccine to prevent HIV infection, sexual behaviour change interventions continue to be an important strategy for controlling the epidemic. These interventions have tended to focus on key behavioural outcomes such as condom use and multiple partner reduction. Delay of sexual debut is also an important outcome, since an early sexual debut has been associated with other sexual risk behaviours such as multiple partners and also increased vulnerability to STIs including HIV.

Measuring biological outcomes in HIV prevention interventions has been increasingly advocated in recent years.^2,3 The limitations of self-reported data, due to measurement error and recall and social desirability biases, are well documented.^4–6 Various techniques have been applied to improve the validity of self-reports. For instance, using audio-computer-assisted-self-interviewing (ACASI) has been shown in some settings to improve the validity of responses in comparison to interviewer or self-administered questionnaires.⁷ However, it has also been argued that there is a need for objective measures to validate self-reports. Although expensive and requiring large samples, the inclusion of biomarker measurements is desirable since reductions in unwanted pregnancy and rates of STIs including HIV are often the ultimate objectives of interventions to improve young people's sexual and reproductive health.⁸

Herpes simplex type 2 (HSV-2) is one of the commonest STIs worldwide and in SSA, and is the primary cause of genital ulcer disease (GUD) worldwide.⁹ It is a lifelong, recurrent infection that is most commonly asymptomatic for a large proportion of the time.^10,11

Studies have shown that sexual risk behaviour, including a young age at sexual debut and multiple sexual partners, are both associated with a higher risk of HSV-2 seropositivity, leading to the suggestion that it could serve as a marker for sexual debut and high-risk sexual behaviour in some circumstances. While the evidence supports its use as a biomarker for high-risk sexual behaviour,^12–14 it is less clear whether it can be used as a biomarker for sexual debut.

HSV-2 is currently the STI most widely advocated for use in evaluating the impact of interventions to reduce sexual risk behaviours, and for use as a marker to validate self-reports of sexual behaviour. Unlike bacterial STIs such as gonorrhoea or syphilis, which can be cured, HSV-2 cannot. In addition, HSV-2 is the most prevalent STI in SSA and, in contrast to bacterial STIs that tend to be highly concentrated in high-risk groups, HSV-2 is more prevalent in the general population.¹⁰ Moreover, while HSV-2 prevalence is on the rise in SSA, bacterial STIs are on the decline.¹⁰ In addition, there are relatively non-invasive testing procedures available, which is an important consideration, especially among young people.

Although other markers are available, such as pregnancy tests and markers of semen exposure such as prostate specific antigen (PSA) and the Y chromosome, testing requires expensive laboratory equipment.¹⁵ In addition, PSA and Y chromosome are not able to indicate unprotected vaginal sex or validate sexual behaviour beyond a maximum of 48 hours and 14 days, respectively;¹⁶ therefore studies employing these methods require large samples. Menstruation, vaginal cleansing, the use of tampons, engaging in coitus interruptus or other related behaviours could potentially interfere with detection.^17–19 An additional disadvantage of using PSA or the Y chromosome is that they can only be used in female participants. The relatively invasive nature of the diagnostic tests for semen exposure (e.g. self-administered vaginal swabs) may also be inappropriate for use among young people, particularly for trials being conducted in school-based settings. Human papillomavirus (HPV) shares many of the characteristics that make HSV-2 a potentially effective biomarker of sexual debut, including high prevalence among sexually active populations and relatively high transmissibility.²⁰ In addition, screening methods such as direct naked-eye visualization of the cervix after acetic acid application (VIA) are more feasible for developing country settings than cervical cytology and HPV DNA testing.²¹ However, although self-collection of cervicovaginal specimens has been shown to be widely accepted by women worldwide, we are unaware of any studies that have used this method among youth or school children, and it is likely that these diagnostic procedures are too invasive and impractical for use among these populations. Finally, similar to PSA and the Y-chromosome, testing for HPV is currently only available for use among women.

The objective of this review was to evaluate the potential of HSV-2 as a biological marker of sexual debut among young people aged 10–24 years. To fulfill this objective, we reviewed studies related to HSV-2 prevalence, transmissibility, serological testing methodology and testing procedures. In each of the following subsections, we describe the ideal characteristics of a potential biomarker and discuss the available evidence concerning HSV-2. The implications of these findings for future studies are then discussed.

FINDINGS

Prevalence of HSV-2 in sexually active people

Ideally, a biomarker for sexual debut should be highly prevalent in sexually active people, as close to 100% as possible. As mentioned previously, worldwide, the prevalence of HSV-2 is highest in SSA;⁹ however, prevalence varies widely between sub-regions, with high prevalence in eastern, middle and southern Africa and lower prevalence in west Africa.⁹ Prevalence is highest among commercial sex workers, bar and factory workers, truck drivers and other high-risk individuals with frequent changes of sexual partner.²²

The majority of studies of HSV-2 prevalence in SSA have used data from antenatal and blood donor clinics or has been restricted to specific high-risk populations and cannot be considered representative of the general population. In addition, the majority of studies among young women have been conducted among young pregnant women, thus little is known about HSV-2 among young women who are not pregnant, or among young men. Indeed, few countries, particularly in SSA, collect data to determine population-based national prevalence estimates of HSV-2.^23,24

Previous reviews of studies in SSA have found that HSV-2 seropositivity is very low in children below the age of 12 years but then increases markedly with age, before plateauing at approximately 40 years of age, with some variation across contexts.^9,22 These findings reflect the fact that HSV-2 infection is lifelong and incurable, and thus cumulative probability of seropositivity increases over time after sexual debut related to the individual's number of sexual acts and number of sexual partners.²⁵ Several studies and reviews suggest that prevalence in adults ranges from 30% to 80% in women and is as high as up to 50% in men.^{9,12,22,23,26,27} Consistently higher prevalence in women than in men is hypothesized to be related to both biological and behavioural factors. Studies show particularly high incidence rates among young women of reproductive age.²⁰

An increasing number of studies have reported HSV-2 prevalence among young people in SSA. Cross-sectional studies have reported HSV-2 prevalence among young people aged 13–24 years ranging from 5% to 53% among young men and young women, respectively.^28–31 In a cohort study in rural Uganda, HSV-2 prevalence was 10% in men aged 15–19 years and 27% among those aged 20–24 years, while among females HSV-2 prevalence was 35% among women aged 15–19 and 74% among those aged 20–24 years.³² Studies among young participants enrolled in trials related to circumcision and STI treatment services in southern and eastern Africa reported HSV-2 prevalence in people aged 15–24 ranging from 6% to 56%.^12,33 In addition, studies conducted among pregnant women between the ages of 15 and 19 in Zimbabwe and Tanzania, found prevalence ranging from 19% to 42%.^26,34 Other studies have reported prevalence ranging from 4% to 22% among orphans aged 15–19 years³⁵ and from 15% to 63% among those attending health or STI clinics.^36–39 A study that investigated HSV-2 prevalence among women workers in bars, guesthouses/hotels, local food handlers, brew shops, grocery shops, disco halls and nightclubs in Tanzania found that HSV-2 prevalence was 47% among those aged 16–19 years ranging to 92% among those aged 30–35 years.⁴⁰ Although other studies have been undertaken, they have not disaggregated the prevalence data for HSV-2 by age so they are not a reliable indicator of prevalence in this age group.^36,41,42

Recently, three trials with school-aged populations in SSA have determined HSV-2 prevalence among young people and measured the impact of sexual and reproductive health interventions on biological outcomes, including HSV-2. Two of these trials measured HSV-2 prevalence at baseline.^43,44 The Stepping Stones trial conducted in South Africa found that the baseline HSV-2 prevalence was 29% among women and 10% among men aged 15–26 years.⁴³ The Regai Dzive Shiri study in rural Zimbabwe, which involved young people with a median age of 15 years at baseline, reported low levels of HSV-2 (0.2% prevalence at baseline) in addition to low levels of other biomarkers of interest, namely HIV and pregnancy.⁴⁴ These data suggest that the intervention was implemented prior to the onset of sexual activity in a substantial proportion of the target population.⁴⁴ Similar to other studies, inconsistency and under-reporting of sexual behaviour was found. For instance, none of the four participants who were pregnant reported having had sexual intercourse.⁴⁴ In the MEMA kwa Vijana trial conducted in rural Tanzania, HSV-2 was not measured at baseline; however, HSV-2 prevalence at first follow up (2001/2002) was 12% in men and 21% in women, and 26% in men and 41% in women at second follow-up (2007/2008).^8,45

Transmissibility of HSV-2

The ideal biomarker for sexual debut would have 100% transmissibility, even if contraceptives including condoms are used. Transmissibility of HSV-2 is influenced by a host of interrelated behavioural and biological factors. The type of sexual act, the use of condoms, number of sex acts, duration of infection in the source partner and awareness of partner's serological status may impact transmission.⁴⁶ A recent pooled analysis of studies of condom use and HSV-2 acquisition demonstrated an approximately 30% risk reduction in both men and women with self-reported consistent condom use.⁴⁷ Other factors may include the impact of temporal variations in viral shedding, time since infection and awareness of the subject's own serological status (both in terms of HSV-2 and HIV), which may influence the use of condoms. HSV-2 transmissibility is also greater from men-to-women than women-to-men and there are differences between the genders in terms of frequency of active herpes recurrences, with more recurrence among men as compared with women making men more infectious.^11,32 It is thought that the majority of HSV-2 transmission is from individuals who are unaware of their HSV-2 serostatus.⁴⁸

To estimate transmission per coital act, studies of discordant couples, mainly conducted in developed country settings, have suggested a range between 0.0005 and 0.022.^49,50 A recent longitudinal study on male circumcision conducted in South Africa estimated the per-sex-act female-to-male transmission probability (FtoMTP) for HSV-2 in an unprotected sexual act for an uncircumcised male in the absence of HIV in either partner was 0.0067 (95% CI: 0.0028–0.014),⁵¹ roughly in the middle of the range within the previous review. The per-partnership male-to-female transmission probability (MtoFTP) was 0.026 (95% CI: 0.014–0.047) for HSV-2: approximately four times higher than the per-sex-act FtoMTP.⁵¹ Male circumcision was associated with a 40% lower HSV-2 acquisition by young men aged 18–24 years in this study, although a review of observational studies had reported this association to be weak (summary relative risk [RR] = 0.88, 95% CI 0.77–1.01).⁵² Finally, the South African circumcision trial found that condom use had an effect in reducing HSV-2 per-partner transmission probability, but little effect on the per-act transmission probability.

Given that HSV-2 can be shed over a larger region of the genital area than other STIs, it has been unclear to what extent correct and consistent condom use can protect against HSV-2 infection.⁵⁰ A study conducted by Wald et al. ⁵⁰ reported that overall, condoms reduced HSV-2 transmission by 25%; however, when findings were examined separately by gender it was found that condoms were protective for women, but not for men. The authors attribute this to previous studies which had found that penile skin is the most common site of shedding of HSV-2 in heterosexual men, whereas the exposure of other parts of men's genitalia to sites of female genital shedding such as vulvar or perianal areas may partially explain the lack of protection afforded by condoms for men.⁵⁰ Overall, the evidence suggests that both condom users and circumcised men may still be at some, albeit reduced, risk of HSV-2 infection, especially considering the reported low and inconsistent condom use among young people.⁵³

These findings suggest that HSV-2 transmission may vary in different contexts and highlight the need for specific research conducted among young people who may be more vulnerable both due to biological immaturity and behavioural factors ranging from incorrect and inconsistent condom use, to lack of awareness of serological status. These factors may reduce condom effectiveness as a barrier and increase the potential of HSV-2 as a biomarker. Based on these estimates of the per-sex-act transmission probability alone, it is clear that HSV-2 would be unlikely to perform well as a marker of sexual debut, since not all first sexual partners will be HSV-2 infected and even when they are, the chances of acquiring HSV-2 infection from them at the first sexual act is far below 100%. It may also be further reduced if a condom is used correctly and consistently.

Transmissibility of HSV-2 via non-sexual practices

To be effective as a biological marker of sexual debut, it would be important that HSV-2 not be transmissible except by penetrative sexual intercourse. HSV-2 is primarily sexually transmitted; however, non-penetrative sexual practices including oral sex may also result in HSV-2 infection, although data on transmissibility by such acts are limited.^54,55 It has been reported that prevalence is ‘negligible’ among those who have never had penetrative sexual intercourse.^14,22 In the rare instances that it does occur, it has been thought likely to have been attributable to a neonatal infection.⁵⁶ Vertical transmission of HSV-2 in pregnancy either in utero or intrapartum may be life-threatening to babies who acquire the virus.⁴⁶ The risk of neonatal infection is highest when HSV-2 infection is acquired by the mother in the last trimester and lowest for those infections occurring in early pregnancy. There is little available evidence on the incidence or prevalence of neonatal HSV-2 infection in SSA. However, a recent study conducted among Tanzanian children and young people demonstrated that 15% of children were infected with HSV-2 by the age of eight years, with prevalence increasing markedly to 40% in those between the ages of 17 and 20 years.³⁷ Although the reasons for the unexpectedly high prevalence among young children are unclear, the authors conclude that the findings suggest that non-sexual transmission of HSV-2 may be higher than previously thought. Another potential explanation may relate to sexual abuse of children. Although the prevalence of sexual abuse before the age of 15 in Tanzania has been reported to be as high as 11%,^57,58 this would not explain a prevalence of 15% among eight-year-olds, unless sexual abuse was substantially under-reported. A recent review concluded that there are insufficient data available to estimate the likelihood of transmission after exposure to sexual abuse of children.⁵⁹

Non-abusive hand-genital contact may occur in a child with active oral lesions leading to autoinoculation, or from care-givers during activities such as bathing and toileting.⁶⁰ Taken together, these findings demonstrate that although the majority of HSV-2 transmission takes place via sexual contact, there are insufficient data to determine the HSV-2 transmission potentials of non-sexual contact.

These data on the prevalence and transmissibility of HSV-2 show that the positive predictive value of HSV-2 seropositivity for sexual debut is likely to be high. In other words, if an individual is HSV-2 positive, the probability that they have had sexual intercourse will be high. However, in a small proportion of individuals with a positive HSV-2 test, this infection will have been acquired through close contact without penetrative sexual intercourse. Conversely, the negative predictive value of HSV-2 for sexual debut will be low. In other words, there is a substantial probability that individuals who test HSV-2-negative will have had their sexual debut.

Serological testing methodology for HSV-2

In considering the potential of HSV-2 as a biomarker for sexual debut, affordable assays will be needed that have specifically been shown to have high specificity and sensitivity among young people, and that have well-defined reference limits. In resource-limited settings, diagnosing HSV-2 by virus culture or DNA amplification methods is not considered feasible due to its complexity and cost.⁶¹ Assays which detect antibodies to HSV-2 specific glycoprotein gG-2 are commercially available;²³ however, their sensitivity and specificity have been shown to vary in different contexts.^23,61

The validation of HSV-2 enzyme immunoassay (EIA) tests is of particular importance since their sensitivity and specificity have been shown to vary in different contexts, and many commercially available EIA kits do not appear to perform adequately in East and Southern African populations.^61–65 So far, even the best-performing commercial EIA (Kalon Biological, Aldershot, UK) only had a sensitivity of 92.3% and specificity of 97.7% in a panel of 330 serum samples from SSA, when using Western blot as the gold standard.⁶⁶ Therefore, if the true prevalence of HSV-2 is 2.0%, then, with a sensitivity of 92.3% and a specificity of 97.7%, the prevalence will be estimated as 4.1%. However, if the true prevalence was 30%, this would be estimated as a prevalence of 29.3%.

Findings from a study conducted among children and young people up to the age of 20 years in Tanzania found that commercial Bionor HSV-2 ELISA tests performed better for youth aged 17–20 years than for younger children, thus it is unclear to what extent available tests are accurate for use in younger populations.³⁷ One study conducted among children between the ages of 1 and 18 years attending a sexual abuse clinic in the USA found that the Focus test produced an unacceptably high number of false-positives, and suggested that Biokit may be a viable alternative to Western blot.⁶⁷ An additional advantage of using Biokit is that it only requires a finger prick, which is desirable as a non-invasive testing procedure for use, perhaps especially in young populations.

Using cut-off points above the standard index values was advocated by several studies for achieving optimal sensitivity and specificity. Although increasing the threshold for diagnosing positive results is one way of improving specificity, this may potentially reduce sensitivity in early infection.⁶¹ These findings show that further studies are needed to address the issue of serological testing methodology and to establish optimal index values for younger populations in SSA. Careful consideration of which test to use and how to use it will be needed by future studies aiming to investigate HSV-2 among younger populations.

Studies intending to collect biological specimens from minors need to adopt standards and procedures which adhere to high ethical standards and which are acceptable to both young people and their parents or care-givers. For instance, the identification of an STI in a child carries both medical and legal implications.⁵⁹ In many countries the presence of an STI in a child requires specific reporting procedures and may raise suspicions of abuse, potentially leading to an investigation. It is notable that few of the intervention studies identified in this review elaborated on the ethical considerations associated with collecting biological specimens from young people under the age of majority including obtaining consent, the risks, benefits and reporting procedures. Standard acknowledgements related to ethics and research clearance only were included, although all of the trials reported having extensive involvement of community advisory boards that provided input and approval related to issues such as consent. In the Regai Dzive Shiri study in Zimbabwe, a feasibility and acceptability study was conducted prior to the school-based HIV prevention intervention. This study sought feedback from students, parents, teachers and the wider community to assess the acceptability of a trial using biological outcomes. The study reported positive findings related to acceptability and feasibility; however, the thornier issues related to consent, confidentiality and privacy were not reported.³ The study utilized urine samples, which are considered to be less invasive than blood samples.

DISCUSSION

While it is clear that the inclusion of biological markers in studies investigating the sexual behaviour of young people is necessary in order to improve the quality of data and assessment of intervention impact, the findings of this review demonstrate that HSV-2 is unlikely to be a good biological marker of sexual debut. If the HSV-2 tests used have a high sensitivity and specificity for the detection of current or past HSV-2 infection, a positive HSV-2 test result is likely to have a high sensitivity for sexual debut, although there is the potential for HSV-2 acquisition in the absence of penetrative sexual intercourse. However, the absence of HSV-2 is not likely to be a reliable indicator that an individual has not had penetrative sexual intercourse due to the relatively low transmission probabilities and the fact that HSV-2 prevalence is not 100% among potential sexual partners.

The studies reviewed here demonstrate that the majority of studies of HSV-2 in SSA have been conducted among populations aged 15 and above, with few investigating its prevalence among younger populations. A number of studies and reviews have found that HSV-2 is highly prevalent in the adult population in SSA, particularly in populations where other STIs including HIV are highly prevalent. These data are important, particularly since age mixing and mixing of risk groups and the general population in sexual relationships is common. Nevertheless, there is also a great need for reliable estimates of prevalence and incidence among young people so that interventions and health services can respond appropriately.

The potential of HSV-2 as a biomarker for sexual debut is also dependent on its transmissibility. Given the range of variables that have been identified as potentially impacting transmissibility, including biological and behavioural factors specifically relevant to young populations, such as correct and consistent condom use, further research is needed to obtain reliable estimates of HSV-2 transmissibility.

For HSV-2 to be considered an effective biomarker, it would also not be transmitted except via penetrative sexual intercourse. Given the lack of research evidence, it is uncertain to what extent it is possible to acquire HSV-2 via non-sexual means. This needs to be determined before HSV-2 seropositivity can be confidently associated with sexual debut.

In addition, assays which have been specifically validated for use among young people, and which are affordable, high in specificity and sensitivity with well-defined reference limits, and minimally invasive, are necessary for HSV-2 to be considered ideal. Since few studies have been conducted among young people in African settings, further data on the performance and acceptability of assays in this population are important.

Finally, there is also a broad spectrum of ethical and legal issues surrounding the collection of biological specimens from young people and this requires careful consideration. For instance, literature on the inclusion of young people in HIV vaccine trials in South Africa highlights the need to consider guardian consent, minimum age of independent consent and confidentiality of in-trial medical results.⁶⁸

Based on the findings of this review, it is clear that HSV-2 is not a perfect biological marker of sexual debut. This is related to the findings that: (a) HSV-2 prevalence among potential sexual partners and transmissibility are usually substantially less than 100%, (b) it is unclear how transmissible the virus is by non-sexual means, (c) reported consistent condom use has been shown to afford some level of protection and (d) there is limited availability of high-performance diagnostic tests which are both affordable and non-invasive.

Nevertheless, given the burden of HSV-2 in SSA and its association with sexual risk behaviour, it is clear that HSV-2 is an important STI outcome that should continue to be measured in intervention studies and further research to fill these gaps in the current knowledge base should be prioritized.

Footnotes

ACKNOWLEDGEMENTS

This review was supported by the PREPARE project. The full title of the project is: ‘Promoting sexual and reproductive health among adolescents in southern and eastern Africa – mobilizing schools, parents and communities’. Acronym: PREPARE. The PREPARE study is funded by the EC Health research programme, Grant Agreement number 241945. The partners and principal investigators include: University of Cape Town (Cathy Mathews), Muhimbili University of Health and Allied Sciences (Sylvia Kaaya), University of Limpopo (Hans Onya), Makerere University (Anne Katahoire), Maastricht University (Hein de Vries), University of Exeter (Charles Abraham), University of Oslo (Knut-Inge Klepp), University of Bergen (Leif Edvard Aarø, coordinator). See also the project homepage http://prepare.b.uib.no/

References

Paul-Ebhohimhen

, Poobalan

, van Teijlingen

. A systematic review of school-based sexual health interventions to prevent STI/HIV in sub-Saharan Africa. BMC Public Health 2008;8:4

Coates

, Richter

, Caceres

. Behavioural strategies to reduce HIV transmission: how to make them work better. Lancet 2008;372:669–84

Cowan

, Langhaug

, Mashungupa

, School based HIV prevention in Zimbabwe: feasibility and acceptability of evaluation trials using biological outcomes. AIDS 2002;16:1673–8

Plummer

, Ross

, Wight

, ‘A bit more truthful’: the validity of adolescent sexual behavior data collected in rural northern Tanzania using five methods. Sex Transm Infect 2004;80(Suppl. 2):49–56

Beguy

, Kabiru

, Nderu

. Inconsistencies in self-reporting of sexual activity among young people in Nairobi, Kenya. J Adolesc Health 2009;45:595–601

Palen

, Smith

, Caldwell

, Flisher

, Wegner

, Vergani

Inconsistent reports of sexual intercourse among South African high school students. J Adolesc Health 2008;42:221–7

Langhaug

, Sherr

, Cowan

. How to improve the validity of sexual behavior reporting: systematic review of questionnaire delivery modes in developing countries. Trop Med Int Health 2010;15:362–81

Ross

, Changalucha

, Obasi

, Biological and behavioural impact of an adolescent sexual health intervention in Tanzania: a community-randomized trial. AIDS 2007;21:1943–55

Looker

, Garnett

, Schmid

. An estimate of the global prevalence and incidence of herpes simplex virus type 2 infection. Bull World Health Organ 2008;86:805–12, Abstract

10.

Abu-Raddad

, Magaret

, Celum

, Genital herpes has played a more important role than any other sexually transmitted infection in driving HIV prevalence in Africa. PLoS One 2008;3:e2230

11.

Freeman

, Weiss

, Glynn

, Cross

, Whitworth

, Hayes

. Herpes simplex virus 2 infection increases HIV acquisition in men and women: systematic review and meta-analysis of longitudinal studies. AIDS 2006;20:73–83

12.

Obasi

, Mosha

, Quigley

, Antibody to herpes simplex virus type 2 as a marker of sexual risk behavior in rural Tanzania. J Infect Dis 1999;179:16–24

13.

Cowan

, Johnson

, Ashley

, Corey

, Mindel

. Antibody to herpes simplex virus type 2 as serological marker of sexual lifestyle in populations. BMJ 1994;309:1325–9

14.

Nahmias

, Lee

, Beckman-Nahmias

. Sero-epidemiological and sociological patterns of herpes simplex virus infection in the world. Scand J Infect Dis 1990;(Suppl. 69):19–36

15.

Mauck

. Biomarkers of semen exposure. Sex Transm Dis 2009;36 (Suppl.):S81–3

16.

Macaluso

, Lawson

, Akers

, Prostate-specific antigen in vaginal fluid as a biological marker of condom failure. Contraception 1999;59:195–201

17.

Gallo

, Behets

, Steiner

, Prostate-specific antigen to ascertain reliability of self-reported coital exposure to semen. Sex Transm Dis 2006;33:476–9

18.

Zenilman

, Yuenger

, Galai

, Turner

, Rogers

. Polymerase chain reaction detection of Y chromosome sequences in vaginal fluid: preliminary studies of a potential biomarker for sexual behavior. Sex Transm Dis 2005;32:90–4

19.

Brotman

, Melendez

, Smith

, Galai

, Zenilman

. Effect of menses on clearance of Y-chromosome in vaginal fluid: implications for a biomarker of recent sexual activity. Sex Transm Dis 2010;37:1–4

20.

Smith

, Melendy

, Rana

, Pimenta

. Age-specific prevalence of infection with human papillomavirus in females: a global review. J Adolesc Health 2008;43(Suppl.):S5–25, S25

21.

Gravitt

, Belinson

, Salmeron

, Shah

. Looking ahead: a case for human papillomavirus testing of self-sampled vaginal specimens as a cervical cancer screening strategy. Int J Cancer 2011;129:517–27

22.

Smith

, Robinson

. Age-specific prevalence of infection with herpes simplex virus types 2 and 1: a global review. J Infect Dis 2002;186(Suppl. 1):S3–28

23.

Paz-Bailey

, Ramaswamy

, Hawkes

, Geretti

. Herpes simplex virus type 2: epidemiology and management options in developing countries. Postgrad Med J 2008;84:299–306

24.

Johnson

, Coetzee

, Dorrington

. Sentinel surveillance of sexually transmitted infections in South Africa: a review. Sex Transm Infect 2005;81:287–93

25.

Schiffer

, Corey

. New concepts in understanding gential herpes. Curr Infect Dis Reports 2009;11:457–64

26.

Yahya-Malima

, Evjen-Olsen

, Matee

, Fylkesnes

, Haarr

. HIV-1, HSV-2 and syphilis among pregnant women in a rural area of Tanzania: prevalence and risk factors. BMC Infect Dis 2008;8:75

27.

Weiss

, Buve

, Robinson

, The epidemiology of HSV-2 infection and its association with HIV infection in four urban African populations. AIDS 2001;15(Suppl. 4):S97–108

28.

Amornkul

, Vandenhoudt

, Nasokho

, HIV prevalence and associated risk factors among individuals aged 13–34 years in Rural Western Kenya. PLoS One 2009;4:e6470

29.

Auvert

, Ballard

, Campbell

, HIV infection among youth in a South African mining town is associated with herpes simplex virus-2 seropositivity and sexual behaviour. AIDS 2001;15:885–98

30.

Mmbaga

, Leyna

, Stray-Pedersen

, Klepp

. Herpes simplex virus type 2 and human immunodeficiency virus infections in a rural population in Kilimanjaro Tanzania. East Afr J Public Health 2011;8:28–32

31.

Shaw

, van der Sande

, West

, Prevalence of herpes simplex type 2 and syphilis serology among young adults in a rural Gambian community. Sex Transm Infect 2001;77:358–65

32.

Kamali

, Nunn

, Mulder

, Van

, Dobbins

, Whitworth

. Seroprevalence and incidence of genital ulcer infections in a rural Ugandan population. Sex Transm Infect 1999;75:98–102

33.

Sobngwi-Tambekou

, Taljaard

, Lissouba

, Effect of HSV-2 serostatus on acquisition of HIV by young men: results of a longitudinal study in Orange Farm, South Africa. J Infect Dis 2009;199:958–64

34.

Munjoma

, Mapingure

, Stray-Pedersen

. Risk factors for herpes simplex virus type 2 and its association with HIV among pregnant teenagers in Zimbabwe. Sex Health 2010;7:87–9

35.

Birdthistle

, Floyd

, Machingura

, Mudziwapasi

, Gregson

, Glynn

. From affected to infected? Orphanhood and HIV risk among female adolescents in urban Zimbabwe. AIDS 2008;22:759–66

36.

Mbizvo

, Msuya

, Stray-Pedersen

, Chirenje

, Munjoma

, Hussain

. Association of herpes simplex virus type 2 with the human immunodeficiency virus among urban women in Zimbabwe. Int J STD AIDS 2002;13:343–8

37.

Kasubi

, Nilsen

, Marsden

, Bergstrom

, Langeland

, Haarr

. Prevalence of antibodies against herpes simplex virus types 1 and 2 in children and young people in an urban region in Tanzania. J Clin Microbiol 2006;44:2801–7

38.

Langeland

, Haarr

, Mhalu

. Prevalence of HSV-2 antibodies among STD clinic patients in Tanzania. Int J STD AIDS 1998;9:104–7

39.

Msuya

, Mbizvo

, Hussain

, Sam

, Jeansson

, Stray-Pedersen

. Seroprevalence and correlates of herpes simplex virus type 2 among urban Tanzanian women. Sex Transm Dis 2003;30:588–92

40.

Watson-Jones

, Weiss

, Rusizoka

, Risk factors for herpes simplex virus type 2 and HIV among women at high risk in northwestern Tanzania: preparing for an HSV-2 intervention trial. J Acquir Immune Defic Syndr 2007;46:631–42

41.

Munjoma

, Kurewa

, Mapingure

, The prevalence, incidence and risk factors of herpes simplex virus type 2 infection among pregnant Zimbabwean women followed up nine months after childbirth. BMC Womens Health 2010;10:2

42.

Kurewa

, Mapingure

, Munjoma

, Chirenje

, Rusakaniko

, Stray-Pedersen

. The burden and risk factors of sexually transmitted infections and reproductive tract infections among pregnant women in Zimbabwe. BMC Infect Dis 2010;10:127–35

43.

Jewkes

, Nduna

, Levin

, Impact of stepping stones on incidence of HIV and HSV-2 and sexual behaviour in rural South Africa: cluster randomised controlled trial. BMJ 2008;337:a506

44.

Cowan

, Pascoe

, Langhaug

, The Regai Dzive Shiri Project: a cluster randomised controlled trial to determine the effectiveness of a multi-component community-based HIV prevention intervention for rural youth in Zimbabwe–study design and baseline results. Trop Med Int Health 2008;13:1235–44

45.

Doyle

, Ross

, Maganja

, Long-term biological and behavioral impact of an adolescent sexual health intervention in Tanzania: follow-up survey of the community-based MEMA kwa Vijana Trial. PLoS Med 2010;7:e1000287

46.

Sacks

, Griffiths

, Corey

, HSV-2 transmission. Antiviral Res 2004;63S1:S27–35

47.

Martin

, Krantz

, Gottlieb

, A pooled analysis of the effect of condoms in preventing HSV-2 acquisition. Arch Intern Med 2009;169:1233–40

48.

Mertz

. Asymptomatic shedding of herpes virus 1 and 2: implications for prevention of transmission. J Infect Dis 2008;198:1098–100

49.

Wald

, Krantz

, Selke

, Lairson

, Morrow

, Zeh

. Knowledge of partners’ genital herpes protects against herpes simplex virus type 2 acquisition. J Infect Dis 2006;194:42–52

50.

Wald

, Langenberg

, Link

, Effect of condoms on reducing the transmission of herpes simplex virus type 2 from men to women. JAMA 2001;285:3100–6

51.

Mahiane

, Legeai

, Taljaard

, Transmission probabilities of HIV and herpes simplex virus type 2, effect of male circumcision and interaction: a longitudinal study in a township of South Africa. AIDS 2009;23:377–83

52.

Weiss

, Thomas

, Munabi

, Hayes

. Male circumcision and risk of syphilis, chancroid and genital herpes: a systematic review and meta-analysis. Sex Transm Infect 2006;82:109

53.

UNAIDS. Global Report on the AIDS Epidemic. Geneva: UNAIDS, 2010

54.

Murata

. Noncoital sexual activity may not be ‘safe’ sex. Obstet Gynecol 2008;112:735–8

55.

Kreimer

, Alberg

, Daniel

, Oral human papillomavirus infection in adults is associated with sexual behavior and HIV serostatus. J Infect Dis 2004;189:686–98

56.

Cowan

, Mindel

. Sexually transmitted diseases in children: adolescents. Genitourin Med 1993;69:141–7

57.

Lalor

. Child sexual abuse in sub-Saharan Africa: a review. Child Abuse Negl 2004;28:439–60

58.

García-Moreno

, Jansen

HAFM

, Ellsberg

, Heise

, Watts

. WHO Multi-Country Study on Women's Health and Domestic Violence Against Women: Initial Results on Prevalence, Health Outcomes and Women's Responses. Geneva: WHO, 2005

59.

Hammerschlag

, Guillen

. Medical and legal implications of testing for sexually transmitted infections in children. Clin Microbiol Rev 2010;23:493–506

60.

Bechtel

. Sexual abuse and sexually transmitted infections in children and adolescents. Curr Opin Pediatr 2010;22:94–9

61.

Van Dyck

, Buve

, Weiss

, Performance of commercially available enzyme immunoassays for detection of antibodies against herpes simplex virus type 2 in African populations. J Clin Microbiol 2004;42:2961–5

62.

Hogrefe

, Su

, Song

, Ashley

, Kong

. Detection of herpes simplex virus type 2-specific immunoglobulin G antibodies in African sera by using recombinant gG2, Western blotting, and gG2 inhibition. J Clin Microbiol 2002;40:3635–40

63.

Smith

, Bailey

, Westreich

, Herpes simplex virus type 2 antibody detection performance in Kisumu, Kenya, using the Herpeselect ELISA, Kalon ELISA, Western blot and inhibition testing. Sex Transm Infect 2009;85:92–6

64.

Laeyendecker

, Henson

, Gray

, Performance of a commercial, type-specific enzyme-linked immunosorbent assay for detection of herpes simplex virus type 2-specific antibodies in Ugandans. J Clin Microbiol 2004;42:1794–6

65.

Gamiel

, Tobian

, Laeyendecker

, Improved performance of enzyme-linked immunosorbent assays and the effect of human immunodeficiency virus coinfection on the serological detection of herpes simplex virus type 2 in Rakai, Uganda. Clin Vaccine Immunol 2008;15:888–90

66.

Mujugira

, Morrow

, Celum

, Performance of the Focus HerpeSelect-2 enzyme immunoassay for the detection of herpes simplex virus type 2 antibodies in seven African countries. Sex Transm Infect 2011;87:238–41

67.

Ramos

, Lukefahr

, Morrow

, Stanberry

, Rosenthal

. Prevalence of herpes simplex virus types 1 and 2 among children and adolescents attending a sexual abuse clinic. Pediatr Infect Dis J 2006;25:902–5

68.

Jaspan

, Soka

, Strode

, Community perspectives on the ethical issues surrounding adolescent HIV vaccine trials in South Africa. Vaccine 2008;26:5679–83