Herpes Simplex Virus Type 2 Infection as a Risk Factor for Human Immunodeficiency Virus Acquisition in Men Who Have Sex with Men

Departments of ¹Medicine, ²Epidemiology, and ³Laboratory Medicine, University of Washington, Seattle; ⁴Denver Department of Public Health, Denver, Colorado; ⁵AIDS Office, San Francisco Department of Public Health, San Francisco, California; ⁶Laboratory of Epidemiology, New York Blood Center, New York; ⁷Department of Psychology, University of Illinois and Howard Brown Health Center, Chicago; ⁸Department of Medicine, Brown University, Providence, Rhode Island; ⁹Research Department, Fenway Community Health Center, Boston, Massachusetts

Received 9 July 2002; revised 20 September 2002; electronically published 13 December 2002.

     Presented in part: 42nd annual Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, California, 2730 September 2002 (abstract 773).
     Written informed consent was obtained from all participants. The human experimentation guidelines of the US Department of Health and Human Services and the individual institutions were followed in conducting the clinical research.
     Financial support: HIV Network for Prevention Trials (National Institutes of Health grant AI-35176); Centers for Disease Control and Prevention Collaborative HIV Seroincidence Study (cooperative agreements U64/CCU900523-11, CCU802715-06, and CCU502714-07); Herpes Program Project (NIH grant AI-30731).
     Reprints or correspondence: Dr. Connie L. Celum, University of Washington HIV Prevention Trials Unit, Harborview Medical Center, Box 359927, 325 Ninth Ave., Seattle, WA 98104 .

     Human immunodeficiency virus (HIV) prevalence and incidence in the United States is highest among men who have sex with men (MSM). Thus, the most effective prevention strategies should be directed toward those factors associated with increased risk of HIV acquisition and transmission in that population. Observed heterogeneity in the per-contact risk of HIV acquisition via sexual exposure is most likely due to variability in biologic factors that alter susceptibility and infectivity [1]. Early studies focused primarily on increased HIV susceptibility and infectiousness that resulted from bacterial sexually transmitted diseases (STDs) [2 5]. In a recent multisite study among MSM, urethritis conferred a 2.3-fold increased risk of HIV acquisition [6]. Other factors associated with HIV acquisition among MSM include sex with an HIV-positive partner, injection drug use, unprotected receptive anal intercourse, condom failure, young age, and lack of circumcision [6 8].

     Herpes simplex virus type 2 (HSV-2), the cause of genital herpes, is considered to be a major factor in geographic differences in HIV prevalence among heterosexual individuals in Africa [9]. A recent meta-analysis of studies primarily conducted among heterosexual populations reported that HSV-2 infection was associated with a 2.1-fold increased risk of HIV acquisition in 9 studies documenting HSV-2 infection before HIV acquisition [10]. However, among MSM, a group in which HSV-2 prevalence is as high as 80% among those with HIV [11] and as high as 50% among those without HIV [12], HSV-2 infection has been observed to be associated with an increased risk of HIV seroconversion in some [13, 14], but not all [15], studies. Differences in these findings may have been due to the limited number of individuals who converted from HIV seronegative to seropositive in prior studies and to challenges in controlling for exposure to HIV using behavioral variables.

     Given recently observed increases in the rates of bacterial STDs [16 18] and HIV incidence [19] among MSM, as well as the high HSV-2 seroprevalence among MSM, there is a critical need to identify modifiable risk factors so that additional strategies to reduce sexual HIV transmission can be developed. We conducted a nested case-control study to examine the association between HSV-2 seropositivity and subsequent risk of HIV acquisition among MSM, to determine whether HSV-2 treatment could serve as a new HIV prevention target in this population.

METHODS

     Study design and population.     A case-control study was performed, nested within 2 multisite cohort studies: the Centers for Disease Control and Prevention Collaborative HIV Seroincidence Study (CHSS) in San Francisco, Denver, and Chicago (19931994) and the National Institute of Allergy and Infectious Diseases HIV Vaccine Preparedness Study (VPS) in San Francisco, Denver, Chicago, Boston, Seattle, and New York (19951997). HIV-seronegative MSM were eligible to participate if they had engaged in anal sex within the past year and were recruited through advertising, outreach activities, STD clinics, HIV testing sites, and referrals from other study participants. Subjects were followed up for 18 months with visits at 6-month intervals and completed semistructured interviews that included questions about risk behaviors and STD symptoms. Study protocols and questionnaires for the studies were similar; a common database was established that included variables assessed in both studies, such as demographic characteristics, sexual behaviors, STD diagnoses and symptoms (rectal, urethral, or pharyngeal gonorrhea or chlamydia or nonspecific urethritis), and injection and noninjection (amphetamines, barbiturates, cocaine, hallucinogens, marijuana, narcotics, and amyl nitrite) drug use in the previous 6 months. Participants were asked about anogenital sores and the anatomic location of any "outbreak of herpes in the last 6 months." HSV serologic testing was performed on stored serum samples, and thus questions about herpes outbreaks were answered without specific knowledge of subjects' HSV serostatus and before any herpes counseling.

     The HIV seroincidence was 2.3/100 person-years and 1.55/100 person-years among 2189 MSM enrolled in the CHSS cohort [6] and 3257 MSM enrolled in the VPS cohort [20], respectively. For our study, we defined "case subjects" as men who were HIV seronegative at baseline and seroconverted to HIV positive during the study, as determined by a positive ELISA result confirmed by a Western blot. Control subjects were selected from the group of men who remained HIV seronegative throughout the study and for whom adequate serum samples were available for HSV testing at the same visit "wave" as the case subjects (to provide a comparable follow-up period for case and control subjects). A total of 131 MSM acquired HIV (59 in the CHSS cohort and 72 in the VPS cohort), of whom 116 (88.5%) had sufficient serum samples stored and had provided consent for subsequent testing of stored serum. Three control subjects were selected for each case subject (n = 348), and complete behavioral and laboratory data were available for 342 of those. Because the number of available control subjects was large, and to avoid overmatching, frequency-matching was used; control subjects were frequency-matched to case subjects by duration of follow-up and report of sexual intercourse with an HIV-positive partner and unprotected receptive anal sex during the year before the last visit (these were identified as the 2 most important risk factors for HIV acquisition in the CHSS and VPS cohorts [6, 21]).

     Laboratory methods.     HSV-1 and HSV-2 serostatus was evaluated by type-specific HSV Western blot, which was performed as described elsewhere [22] by technologists at the University of Washington (Seattle) who were blinded to the subjects' case-control status. If HSV-2 antibodies were detected in both the first and the last serum samples, a participant was considered to have prevalent HSV-2 infection. If the serum sample from the last visit was HSV-2 seropositive and the first sample was HSV-2 seronegative, a participant was considered to have incident HSV-2 infection. For these subjects, all interim samples were tested to determine the visit at which HSV-2 antibodies were first detected.

     Statistical analysis.     The primary exposure of interest was HSV-2 seropositivity (either prevalent or incident HSV-2 infection), defined by positive results of an HSV-2 Western blot before HIV seroconversion or, for control subjects, the last visit "wave." Groups were compared using ² statistics for categorical variables and Wilcoxon rank sum statistics for continuous variables. Logistic regression analyses were used to examine univariate associations between HIV seroconversion and demographic characteristics; injection and noninjection drug use; self-reported STD symptoms, diagnoses, and anogenital herpes outbreaks in the past 12 months; and HSV-1 and HSV-2 serostatus. Sexual risk behaviors included number of sexual partners and frequency of receptive and insertive unprotected anal sex (continuous variables) and HIV-positive sexual partners, partners of unknown HIV status, and condom breakage (dichotomous variables) in the past 12 months. Information about sexual risk behaviors and STDs was collected at semiannual visits; an average measure was created for the 12-month period prior to HIV seroconversion among case subjects and the comparable period among control subjects, as was done in initial analyses from the CHSS [6].

     Multivariable logistic regression analyses were performed to assess the association between HIV seroconversion and prior HSV-2 infection, controlling for factors potentially related to likelihood of HIV exposure (condom breakage, any HIV-positive partner or partner of unknown HIV status in the prior 12 months, number of sexual partners, and frequency of unprotected receptive anal intercourse); variables thought a priori to be potential confounders of the association between HIV infection and HSV-2 serostatus (age and bacterial STD or reported herpes outbreak in the past 12 months); race/ethnicity; health insurance (reflecting possible differences in access to health care or health careseeking behaviors); city of recruitment; and year of HIV seroconversion (or last isit, for control subjects). Furthermore, to more directly assess the role of HSV-2 in sexual acquisition of HIV, we excluded from the analysis of this association 16 men who reported injection drug use in the previous 12 months. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using the regression coefficients and standard errors obtained from the logistic regression analyses.

RESULTS

     Case subjects who acquired HIV during the study period were more likely than control subjects to be of a racial or ethnic minority, less likely to have health insurance coverage, and more likely to report injection drug use . For the 12-month period preceding seroconversion, case subjects also reported a higher number of sexual partners than did control subjects (median, 6.5 vs. 4.5 partners; P = .008) and a higher frequency of unprotected receptive anal sex (median, 3 vs. 1.5 episodes; P = .004) and any condom breakage (39% vs. 29%; P = .05). Whereas case and control subjects were similar with respect to HSV-1 seropositivity and self-reported bacterial STDs in the past 12 months , a higher proportion of case subjects were HSV-2 seropositive at the initial visit (41% vs. 31%). In addition, among subjects who were HSV-2 seronegative at baseline, 5 (7.4%) of 68 case subjects and 9 (3.8%) of 236 control subjects acquired HSV-2 during follow-up. Thus, in summary, 46% of case subjects were HSV-2 seropositive before HIV seroconversion, compared with 34% of control subjects before their last visits (P = .03).

fig.ommitted

Table 1.          Sociodemographic characteristics and sexual and drug use behaviors among 116 men who have sex with men and who seroconverted to human immunodeficiency virus (HIV) positive during the study (case subjects) and 342 control subjects.

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Table 2.          Herpes simplex virus type 2 (HSV-2) and HSV-1 serostatus, bacterial sexually transmitted diseases (STDs), and herpes symptoms among 116 men who have sex with men and who seroconverted to human immunodeficiency virus (HIV) positive during the study (case subjects) and 342 control subjects.

     Overall, 6.0% of case subjects and 11.4% of control subjects reported herpes symptoms in the previous 12 months (P = .1; ), a trend that, although it was not statistically significant, was observed among both HSV-2seropositive subjects (7.6% vs. 18.1%) and HSV-2seronegative subjects (4.8% vs. 8.0%). Only 1 of the 14 subjects who seroconverted to HSV-2 during the study (a control subject) reported having symptoms consistent with genital herpes during the past 12 months. Eighteen of the 21 HSV-2seronegative MSM who reported anogenital lesions or herpes symptoms were HSV-1 seropositive, which suggests that their symptoms may have been due to HSV-1 reactivation.

     In a multivariable logistic regression analysis assessing the association of HIV seroconversion with prior HSV-2 infection, we found prior HSV-2 seropositivity to be associated with a 1.8-fold increased risk of HIV seroconversion (95% CI, 1.12.9; adjusted for age, lack of health insurance, and self-reported risk behaviors in the previous 12 months; ). Having >12 (compared with <3) sexual partners in the previous year (OR, 2.9; 95% CI, 1.46.3), lack of reported herpes outbreaks in the past 12 months (OR, 0.3; 95% CI, 0.10.8), and lack of health insurance (OR, 2.3; 95% CI, 1.43.8) were also independently associated with HIV acquisition. Although men who reported having herpes symptoms within the past 12 months had a higher median number of sexual partners than men who did not report such symptoms (9 vs. 4.5; P < .001), no significant differences in the proportion reporting any unprotected receptive or insertive anal intercourse were observed. Self-reported bacterial STDs within the past 12 months did not appear to increase the risk of HIV seroconversion. The association of HSV-2 seropositivity with HIV acquisition did not change when the 16 MSM who reported injection drug use in the previous year were included (OR, 1.8; 95% CI, 1.12.9). No interactions between HSV-2 infection and clinical, demographic, and behavioral variables were found.

fig.ommitted

Table 3.          Likelihood of human immunodeficiency virus (HIV) seroconversion in association with previous herpes simplex virus type 2 (HSV-2) seropositivity among noninjection drugusing men who have sex with men.

     To examine the association between HIV acquisition and subclinical HSV-2 infection, we performed a multivariable analysis among case and control subjects who did not report having anogenital herpes symptoms in the previous 12 months. These results were similar to the findings described above; previous HSV-2 seropositivity was associated with a 1.7-fold increased risk of HIV acquisition (95% CI, 1.02.9). Finally, to assess the association between recent HSV-2 infection and HIV acquisition among subjects who were HSV-2 seronegative at the initial visit, we compared the odds of HIV acquisition among men who did versus men who did not seroconvert to HSV-2 positive during follow-up (adjusted OR, 2.8; 95% CI, 0.810.1; P = .11).

DISCUSSION

     In this nested case-control study of HIV-negative MSM in 6 US cities who were followed prospectively for 18 months, previous HSV-2 infection was associated with a 1.8-fold increased likelihood of HIV acquisition, independent of various sociodemographic characteristics, sexual behaviors, and self-reported bacterial STDs in the past 12 months, which is similar to recent findings among heterosexual men and women [10, 23 25] and MSM [13, 14, 26]. Because HSV-2 and HIV could conceivably be acquired from the same sexual exposure, we evaluated the risk of HIV acquisition after HSV-2 seroconversion to more accurately estimate the effect of HSV-2 reactivation on HIV susceptibility. Furthermore, the increased risk of HIV acquisition due to herpes infection was specific to HSV-2 and not to HSV-1 infection. A greater number of sexual partners, lack of reported herpes outbreaks in the past 12 months, and lack of health insurance were also independently associated with HIV acquisition. Lack of health insurance could be associated with unmeasured socioeconomic or behavioral factors or with health careseeking behaviors and access to health care, which might be associated with recognition of herpes symptoms or other STDs. Because case and control subjects were frequency-matched by report of unprotected receptive anal intercourse and HIV-positive partners in the prior 12 months, the association between these factors and HIV seroconversion could not be evaluated.

     This study is, to our knowledge, the largest published analysis of HSV-2 infection and HIV acquisition among MSM; it included more than twice as many HIV seroconverters as previously published studies. We found an HSV-2 seroprevalence of 46% before HIV acquisition among subjects who seroconverted during the study, which is comparable to the seroprevalence reported in case-control studies conducted by Kingsley et al. [15] (43%) and Holmberg et al. [13] (45%) but somewhat lower than that reported by Keet et al. [14] (68%). HSV-2 seropositivity was significantly associated with HIV acquisition risk in the studies by Holmberg et al. [13] (OR, 2.6; 95% CI, 1.25.9) and Keet et al. [14] (OR, 4.0; 95% CI, 1.79.8), but no association was found in the Multicenter AIDS Cohort study (MACS; OR, 1.0; 95% CI, 0.32.9 [15]). Differences in these findings could be due to the inclusion of a smaller number of subjects who seroconverted or to confounding by unmeasured behavioral factors for which the analysis was not controlled.

     The strengths of our study included our ability to document HSV-2 infection before HIV acquisition and to assess confounding by a number of important variables. Control subjects were frequency-matched to case subjects by report of sexual intercourse with an HIV-positive partner or unprotected receptive anal sex during the previous year (the 2 most important risk factors for HIV acquisition identified in the CHSS and VPS cohorts, the studies from which our subjects were drawn) and duration of follow-up (to ensure that case and control subjects had similar periods of follow-up in which acquisition of HIV might occur). In addition, we were able to control for other important factors, including age, race/ethnicity, access to health care, city of enrollment, condom breakage, having a partner of unknown HIV status, number of sex partners, frequency of unprotected receptive anal intercourse, reported anogenital herpes symptoms, and self-reported bacterial STDs. However, the possibility that residual confounding due to unmeasured risk factors occurred cannot be excluded. Furthermore, because relatively few MSM acquired HSV-2 during follow-up, our study had limited power to compare HIV acquisition risk among those with incident HSV-2 infection with the risk among those with prevalent HSV-2 infection. However, our finding that there is a potentially greater risk of HIV acquisition associated with incident HSV-2 infection is similar to observations reported from a study of heterosexual individuals in Pune, India [27], and is consistent with the longer duration and higher frequency of HSV-2 reactivation that occurs in the first year after HSV-2 acquisition [28].

     A minority of HSV-2seropositive MSM in the present study (7.6% of case subjects and 18.1% of control subjects) reported herpes lesions or symptoms in the prior 12 months, which is similar to the proportions reported by Keet et al. [14] (22%) and Holmberg et al. [13] (15%) but higher than those observed in the MACS cohort (4% of HIV-positive and 2% of HIV-negative HSV-2seropositive MSM) [15]. Low proportions of individuals reporting genital herpes symptoms are also observed in general populations (in studies done in the United States), in which up to 90% of HSV-2seropositive persons fail to report a history of genital herpes [29 32]. Furthermore, the similar frequency of subclinical HSV-2 reactivation among persons with and without a history of genital herpes symptoms [33] suggests that HSV-2 likely increases HIV susceptibility, even among HSV-2seropositive persons who do not recognize or report herpes episodes. Our finding of a 1.7-fold increased risk of HIV acquisition among MSM who did not report having herpes lesions or symptoms in the prior 12 months supports this hypothesis. Our observation of a lower risk of HIV seroconversion among individuals who reported recent herpes recurrences might result from men being less likely to engage in unprotected sexual intercourse when they recognize herpes symptoms or from use of suppressive antiviral therapy among MSM with recurrent herpes episodes. We were not able to directly assess these hypotheses, however, because of a lack of information about use of suppressive therapy and timing of HSV symptoms in relation to sexual intercourse. Thus, given the low proportion of HSV-2seropositive MSM who reported a history of genital herpes symptoms and given the potential difficulty in recognizing perianal herpes reactivation, serologic testing may be an important component of prevention strategies aimed at identification of HSV-2infected MSM.

     We and others [10, 13, 14] have not found that the risk of HIV acquisition is increased among individuals infected with HSV-1, even though HSV-1 appears to account for an increasing proportion of initial anogenital HSV infections among MSM [34]. HSV-1 may be associated with a very modest increase in HIV susceptibility; 86% of the HSV-2seronegative MSM in the present study who reported having anogenital herpes symptoms in the prior 12 months were HSV-1 seropositive. However, the attributable risk of HIV acquisition associated with HSV-1 is likely less than that associated with HSV-2, because HSV-1 reactivates much less frequently than HSV-2.

     HIV acquisition was associated with an increased number of partners but not with increased frequency of unprotected receptive anal sex. We did not find bacterial STDs to be an independent risk factor for HIV acquisition, which may be partly the result of the fact that bacterial STDs were ascertained by self-report and not by laboratory assay. Because anorectal gonococcal and chlamydial infections among MSM are often asymptomatic [18], self-reporting likely leads to underestimation of the true prevalence of bacterial STDs. However, it is important to note that a recent resurgence of bacterial STDs has been observed among MSM [16, 18], perhaps increasing the relative contribution of these STDs to HIV acquisition or transmission risk [19]. Clearly, given the limitations of self-reporting of sexual behaviors and STDs and the varying ability to adequately control for confounding in case-control studies, our findings support HIV prevention strategies aimed at reducing numbers of partners and occurrences of unprotected anal sex, as well as the diagnosis and treatment of bacterial STDs among MSM.

     The finding of an almost 2-fold increased risk of HIV acquisition among HSV-2seropositive MSM, independent of other sexual risk factors, underscores the need to evaluate, among high-risk MSM, the efficacy of interventions to reduce HSV-2 acquisition and suppress HSV-2 reactivation as potential HIV prevention strategies. HSV-2 seroprevalence is as high as 70% among MSM in Latin America and heterosexual women in sub-Saharan Africa [9, 23 25]. HSV-2 reactivates in the majority of infected persons, even in the absence of recognized lesions [12, 30, 31, 35, 36]. Moreover, epidemiologic studies suggest that, in populations with high HSV-2 seroprevalence rates, HSV-2 accounts for a substantial proportion of new HIV infections [10]. Given the low proportion of persons with HSV-2 infection who recognize lesions, more widespread use of type-specific HSV serologic tests should be recommended for populations at substantial risk of HIV acquisition. Acyclovir is relatively inexpensive, available in generic formulations, safe, and very well tolerated and suppresses asymptomatic as well as symptomatic HSV reactivation. Suppressive antiviral therapy among HSV-2seropositive persons who are at high risk of HIV infection will be tested for efficacy in preventing HIV acquisition as a "proof of concept" in a National Institutes of Healthfunded multicenter trial beginning in 2003. Although use of antiviral agents for episodic therapy would be less costly and easier to implement as an HIV prevention strategy, it is also likely to be less effective in preventing HIV acquisition than daily suppressive therapy, given the high proportion of subclinical HSV-2 reactivation. Both approaches to HSV-2 prevention warrant testing to determine relative efficacy and public health impact.

Acknowledgments

     We appreciate the helpful review of the manuscript provided by Anna Wald and William Whittington, the assistance of Paul Farley in manuscript preparation, and the invaluable contribution of the study participants.

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