- F M Cowan,
- A M Johnson,
- R Ashley,
- L Corey,
- A Mindel
- Academic Department of Genitourinary Medicine, University College London Medical School, London WC1E 6AV Department of Laboratory Medicine, Division of Virology, Children's Hospital Medical Center, PO Box C-5371, Seattle, WA 98105, USA.
- Correspondence to: Dr Cowan.
- Accepted 23 August 1994
Objectives: To examine the epidemiology of antibody to herpes simplex virus type 2 and to assess its suitability as a serological marker of sexual behaviour in populations with high and low prevalences.
Design: Cross sectional survey.
Setting: Department of genitourinary medicine and blood donation centre in central London.
Subjects: Representative sample of 869 patients attending department between November 1990 and December 1991, and 1494 consecutive blood donors attending for donation between February and April 1992.
Method: Participants had a blood sample taken for antibody testing with a novel type specific assay and completed a questionnaire. Results - Prevalence of antibody differed significantly between the two groups (188/833 (22.7%) clinic attenders; 102/1347 (7.6%) blood donors). In both populations antibody was strongly associated with sex, sexual orientation, years of sexual activity, number of lifetime sexual partners, and past infection with sexually transmitted diseases after other factors were controlled for. Only 130 (45%) of all those with antibody had symptoms suggestive of genital herpes, and 79 (27.4%) had had genital herpes diagnosed. Of those without antibody to herpes simplex viruses type 1 and 2, 8.0% reported genital blisters or sores and 1.1% had had genital herpes diagnosed by a doctor.
Conclusions: The strong relation between herpes simplex virus type 2 and sexual lifestyle suggests that the presence of antibody to the virus may be suitable for use as an objective, serological marker of patterns of sexual behaviour in different populations. These data show that only a minority of those infected with herpes simplex virus type 2 have a diagnosis of genital herpes or express clinical symptoms, making serological determinants of infection essential for epidemiological studies.
Changes in population sexual behaviour are important in the epidemiology of sexually transmitted diseases
So far data have been available only from the results of questionnaires
Antibody to herpes simplex virus type 2 can be detected by a new type specific test
Presence of antibody to herpes simplex virus type 2 correlates highly with sexual lifestyle comprising risk behaviour for sexually transmitted diseases
This test will in the future be a useful tool in the epidemiology of sexually transmitted diseases
There has been increasing interest in measuring sexual behaviour to aid understanding of the transmission dynamics of sexually transmitted diseases, including HIV infection. In particular there is a need for a simple measure to assess differences in behaviour between societies and changes over time. The most commonly used method for assessing sexual lifestyle has been by questionnaire, but this approach is expensive, time consuming, and subject to measurement error.1 If a serological marker were available which could be used as a proxy marker of past sexual behaviour it could be used to monitor changes in behaviour in populations, measure differences in levels of high risk sexual activity between populations, and control for the confounding effect of sexual lifestyle in epidemiological studies. Nahmius et al have suggested that antibody to herpes simplex virus type 2 might prove to be such a marker.2
Epidemiological studies of people with clinically apparent genital herpes indicate that herpes simplex virus type 2 is almost always sexually transmitted.2 Studies of transmission of genital herpes confirm that asymptomatic, unrecognised infection with herpes simplex virus type 2 is common.3,4 Although infection results in lifelong persistence of antibody, determining the extent and epidemiology of asymptomatic infection has been hampered by the absence of a serological test which could accurately detect the antibodies. Such assays have now been developed.
We report the results of a cross sectional seroepidemiological study of herpes simplex virus among attenders of genitourinary medicine clinics and blood donors performed by using a new type specific test for antibody to herpes simplex virus.5 We examined the relation between infection, symptomatology, demographic variables, and lifetime sexual behaviour to assess the suitability of antibody to herpes simplex virus type 2 as a serological marker of sexual lifestyle.
Eligible patients were all those presenting to systematically selected routine sessions at a genitourinary medicine clinic in a central London hospital with a new clinical problem and who were having a blood sample taken for other reasons. All eligible patients were invited to participate. Study clinics were selected so that each of the three daily clinical sessions were equally represented.
Participants gave written, consent, completed a structured questionnaire, and had a serum sample taken for testing for antibody to herpes simplex virus. The questionnaire included demographic details and sexual history (sexual orientation, age at first sexual intercourse, number of lifetime sexual partners, and history of sexually transmitted disease). Participants were also asked if they had genital herpes and or symptoms suggestive of genital herpes.
Consecutive blood donors attending a session in central London were also recruited to the study. They gave verbal consent and had a blood sample taken for testing for antibody to herpes simplex virus. To maximise the response rate a shortened version of the genitourinary medicine questionnaire was administered. The questions used in the present analysis were identical in both versions. Donors were assured that none of the information collected on individual donors would be made available to the Blood Transfusion Service.
Type specific antibodies to herpes simplex virus types 1 and 2 were detected by means of a modified western blot technique. The laboratory methods have been described in detail elsewhere.5 Briefly, serum samples from patients were incubated overnight with cell proteins from both types of the virus which had been separated by electrophoresis and transferred on to nitrocellulose strips. Bound antibodies were detected by antihuman antibody and 4-chloronaphthol. Each run included four serum controls (positive for antibody to herpes simplex virus type 1; positive for antibody to herpes simplex virus type 2; positive to antibody to herpes simplex virus type 1 and herpes simplex virus type 2 and negative to herpes simplex virus). Results were expressed as positive or negative for herpes simplex virus type 1 and herpes simplex virus type 2 by using previously published criteria.5 As antibody titres are not related to degree or frequency of exposure to herpes simplex virus, they were not measured. This assay has been shown to be sensitive and specific for identifying subjects with past herpes simplex virus type 1 and herpes simplex virus type 2 or coinfected with both agents.5
The data were analysed by using SPSS6 and EGRET.7 Duration of sexual activity and lifetime number of sexual partners were divided into five categories. Early age at first sexual intercourse was defined as first intercourse before 16 years.
Multiple logistic regression with seropositivity for herpes simplex virus as the dependent variable was used to examine the independent effect of demographic variables, sexual behaviour, and past sexually transmitted diseases. Only variables found to be significantly associated with the presence of antibody on univariate analysis were included in the model. As age and years of sexual activity were strongly correlated and any effect attributable to age was likely to reflect years of sexual activity, age was not included in the model. The distribution of number of lifetime sexual partners was highly skewed and therefore log10 (lifetime number of sexual partners) was included in the model rather than the actual number of partners. The results are expressed as the odds of seropositivity for herpes simplex virus after controlling for confounders.
The relation between antibody to herpes simplex virus, symptoms, and a diagnosis of herpes was examined (X2 for difference in proportions).
Eight hundred and sixty nine of 887 (98%) attenders at genitourinary medicine clinics and 1494 of 1524 (98%) blood donors who were eligible to participate agreed to do so.
Among clinic attenders, sufficient serum was available for antibody testing in 347 women, 294 heterosexual men, and 192 homosexual men. The median (range) age of women was 25 (17-68) years, of heterosexual men was 29 (17-68) years, of homosexual men was 29 (19-69) years. Of the 833 participants, 535 (64.2%) were single and 789 (84.6%) were white. The prevalence of antibody to herpes simplex virus type 2 was 188/833 (22.7%; 95% confidence interval 19.9 to 25.5%). Table I shows the prevalence of herpes simplex virus type 2 by sex and sexual orientation.
Serum samples were available for antibody testing in 639 women and 708 men. Men who have sex with other men are asked not to donate blood. The median (range) age of women was 30 (18-68) years and of men was 36 (18-68) years. Two hundred and forty eight (35%) men and 326 (51%) women were single, and overall 1266 (94%) were white. The overall prevalence of antibody to herpes simplex virus type 2 was 102/1347 (7.6%; 95% confidence interval 6.2% to 9.0%). Table I shows the prevalence of antibody to herpes simplex virus type 2 by sex.
The prevalence of antibody to herpes simplex virus type 2 was significantly higher in clinic attenders than blood donors (odds ratio 3.6; 95% confidence interval 2.8 to 4.6) and among women and homosexual men than among heterosexual men.
Table II shows the univariate relation between antibodies to herpes simplex virus, demographic characteristics, and sexual lifestyle for clinic attenders and blood donors. There was a strong association between the presence of antibody to herpes simplex virus type 2 and sexual lifestyle. For all groups the prevalence of positive results increased with increasing duration of sexual activity, increasing number of lifetime sexual partners, and increasing number of past infections with other sexually transmitted diseases. Early age at first sexual intercourse was not associated with presence of antibodies in any of the groups studied.
Among clinic attenders antibodies to herpes simplex virus type 2 were associated with increasing age (figure). While this relation was also observed in younger blood donors, there was a decline in prevalence of antibody to herpes simplex virus type 2 with age among older donors.
Table III shows the association between antibody to herpes simplex virus type 2 and demographic and sexual behaviour variables after we controlled for confounding by using multivariate analysis. There was a strong independent association between presence of antibody and increasing years of sexual activity, increasing number of lifetime sexual partners, and a history of sexually transmitted diseases in both blood donors and clinic attenders. Female sex was also independently associated with antibodies to herpes simplex virus type 2.
Fifty nine of 184 (32.1%) clinic attenders with antibody to herpes simplex virus type 2 detected had a history of genital herpes compared with only 19 of 100 blood donors (P<0.001). Likewise, clinic attenders with antibody to herpes simplex virus type 2 were more likely to have symptoms suggestive of genital herpes than blood donors (98 (52.0%) clinic attenders, 31 (30.0%) blood donors). In contrast, among subjects negative for antibodies to herpes simplex virus 50 (20.2%) clinic attenders and 26 (3.4%) blood donors reported genital sores or blisters, and eight (3.3%) and two (0.3%), respectively, had a clinical diagnosis of genital herpes.
This is the first epidemiological study in Britain to use a reliable type specific antibody test for herpes simplex virus type 2. It is one of the first to include men and the only survey to include a low risk population of blood donors. The two important implications of the study are, firstly, that the presence of antibody to herpes simplex virus type 2 has a strong graded association with sexual behaviour, particularly among blood donors, and as such may be a useful serological marker of sexual experience in the general population. Secondly, most of those infected with herpes simplex virus have no symptoms or are unaware of their infection; data that relate antibody status to a history or symptoms of herpes suggest that clinical, non-serological methods of determining past infection are insensitive and poorly specific when compared with reliable serological techniques.
The weight of evidence from clinical and seroepidemiological studies suggests that herpes simplex virus type 2 is almost always transmitted as a result of sexual contact.2,8 This, coupled with its strong association with lifetime sexual experience in populations both at high and low risk of acquiring sexually transmitted diseases, makes it suitable for use as a serological marker of sexual behaviour in populations. In our study the prevalence of herpes simplex virus type 2 was higher among attenders of genitourinary medicine clinics than blood donors, reflecting the clear difference in sexual lifestyle between the two groups. (Clinic attenders were younger at first sexual intercourse, had had more lifetime sexual partners (median number of lifetime partners: clinic attenders 13; blood donors four), and were more likely to have had a sexually transmitted disease in the past than blood donors.)
The prevalence of antibody to herpes simplex virus type 2 among our clinic attenders was lower than that found among attenders of clinics for sexually transmitted disease in Seattle9; however, users of clinics in the two countries are not comparable. A population based survey in the United States found the prevalence of antibody to herpes simplex virus type 2 to be 16.4% in adults, which is higher than among blood donors in London.10 Studies in the United States among attenders of family planning clinics and college students have suggested a similar relation between sexual behaviour and prevalence of antibody to herpes simplex virus type 2,11,12 while a population based study of AIDS in San Francisco has shown that antibody to herpes simplex virus type 2 was associated with risk factors for acquisition of sexually transmitted diseases.13
Female sex was independently associated with the presence of antibody to herpes simplex virus type 2, probably explained by the evidence of Mertz et al, who examined risk factors for transmission of genital herpes and found higher efficiency of transmission from male to female than from female to male.14
Among clinic attenders the prevalence of antibody to herpes simplex virus type 2 increased with age. In blood donors the prevalence also increased with age but only until the fifth and sixth decade, when it declined. This is consistent with changing patterns of sexual lifestyle in successive birth cohorts characterised by increasing numbers of partners and earlier age at first sexual intercourse.15
Both symptoms and a history of genital herpes were insensitive measures of prior exposure to herpes simplex virus type 2. (Several centres have reported a high prevalence of genital herpes due to herpes simplex virus type 1, but 16.5% of study participants with a history of genital herpes had antibodies to herpes simplex virus type 1 alone (data not shown).16,17) Whereas the proportion of clinic attenders positive for antibody to herpes simplex virus type 2 who gave a history of genital herpes was similar to that found in women attending clinics for sexually transmitted disease and university students in Seattle9 the proportion of blood donors positive for antibody to herpes simplex virus type 2 with a history of genital herpes was significantly lower. This is probably explained by selection bias in those attending genitourinary medicine clinics, who are likely to present for management of symptomatic disease.
This study suggests that non-serological methods of determining past infection with herpes simplex virus type 2 have unacceptably high rates of false negative and false positive results for use in clinical and epidemiological studies when compared with reliable type specific serological assays. As commercially available enzyme immunoassays have been shown to give misleading results about herpes simplex virus subtypes and reliable type specific testing for antibody to herpes simplex virus is currently limited to a few research laboratories worldwide,18 its use is confined to that of a research tool (for example, in vaccine trials for herpes simplex virus), but it may have wider applications in the future. At present type specific antibody testing for herpes simplex virus is not routinely available to assist in management of patients with herpes infection or their sexual partners.
The presence of antibody to herpes simplex virus type 2 is objective evidence that a person has been directly or indirectly exposed to high risk sexual behaviour. It may be as good as other simple measures of sexual lifestyle in populations such as number of sexual partners. This is not specific for exposure to a sexually transmitted disease and alone does not measure other aspects of behaviour such as use of condoms or characteristics of partners. The greater specificity of antibody to herpes simplex virus type 2 for other aspects of risk behaviour is suggested by the independent association with a history of other sexually transmitted diseases after lifetime number of partners is controlled for. Antibody to herpes simplex virus type 2 may thus serve as an adjunct to behavioural surveys.
While the presence of antibody to herpes simplex virus type 2 does not predict the sexual behaviour of a person, its population prevalence gives information about the pattern of sexual behaviour within that population. As a marker of sexual lifestyle, antibody to herpes simplex virus type 2 has the advantage that the prevalence in the population is not influenced by changes in provision of services or treatment (as in the case of gonorrhoea or syphilis). Though it will be a poor indictor of recent change in behaviour in older age groups who may have acquired infection long ago, secular changes in age specific prevalence of herpes simplex virus type 2 may be attributed to changes in behaviour in young sexually active populations. In addition, comparison of age specific rates between populations may give an indication of the relative levels of high risk sexual behaviour. Young people are the group at greatest risk of acquiring infection through their sexual behaviour.19 It is in this group that there is greatest need to reduce the negative outcomes of sexual lifestyle, as was highlighted recently in targets set by the government's Health of the Nation.20 Antibody to herpes simplex virus type 2 may serve as a useful new indicator of adoption of practices to reduce risk.
FMC was funded by a Wellcome Trust training fellowship in clinical epidemiology. We thank Anne Cent for her help with the serological tests and Camden and Islington Community Health Care Trust for support.