More than a third of Kenyan men and women are infected with herpes simplex virus type 2 (HSV-2), as are eight in 10 individuals with HIV-1, according to a nationally representative household study.1 Furthermore, among HSV-2–infected individuals, 16% are also infected with HIV, whereas 2% of those without herpes have HIV. Characteristics associated with herpes infection include being female, HIV-positive, older or an uncircumcised male, or having an uncircumcised male partner.

Previous research has established that a synergistic relationship exists between HSV-2 infection and HIV transmission and acquisition, and that populations with high HSV-2 prevalence often have high rates of HIV infection. Few population-based estimates of HSV-2 prevalence exist for Sub-Saharan Africa, which has the world’s highest rates of HIV. The present study, conducted in 2007, was Kenya’s first nationally representative survey to assess the prevalence of these two infections; interviewers collected data on participants’ social and demographic characteristics, history of STIs and sexual behavior, and obtained blood samples for HIV-1, HSV-2 and syphilis testing. In addition to assessing the prevalence of HIV and HSV-2, researchers used logistic regression analysis to identify associations between respondents’ characteristics and herpes infection.

Among the 15,707 Kenyans aged 15–64 who completed interviews and were tested for both HIV and herpes, 35% were infected with HSV-2 (42% of women and 26% of men); of these respondents, 16% were also HIV-positive, compared with only 2% of those who did not have herpes. Of the 1,100 HIV-infected respondents, 81% also had herpes. Respondents who tested positive for HIV-1 were more likely to have HSV-2 than those who tested negative (84% vs. 38% among women, and 74% vs. 24% among men); similarly, respondents who tested positive for syphilis were more likely to have HSV-2 than those who received negative test results (78% vs. 41% among women, and 63% vs. 26% among men). In addition, herpes prevalence increased with age for both genders, and was higher among women than among men for each age-group. Between ages 15 and 24, herpes prevalence rose rapidly among females, from 7% to 34%, while it increased relatively gradually among males, from 3% to 14%. HIV prevalence was also consistently higher among women than among men; among 24-year-olds, for example, infection rates were 11% and 2%, respectively.

As expected, HSV-2 prevalence was higher among respondents who had had two or more lifetime sex partners, rather than none or one partner (55% vs. 26% for women, and 30% vs. 10% for men). Prevalence increased linearly by number of lifetime partners among both genders, but was consistently higher among women. Among men who had been sexually active during the past year, those who reported symptoms of genital ulcer disease in this period were more likely to test positive for HSV-2 (56% vs. 26%). Notably, circumcised men were less likely than their uncircumcised peers to have herpes (24% vs. 39%); similarly, women whose partners were circumcised were less likely to test positive for the virus than were those whose partners had not undergone the procedure (39% vs. 77%). Furthermore, men who had used a condom at last sex had a reduced rate of herpes infection (19% vs. 34%).

In the multivariate analysis, HSV-2 infection was associated with testing positive for HIV (adjusted odds ratios, 7.5 for women and 4.4 for men) and syphilis (3.5 and 2.4, respectively). Age was also correlated with herpes infection: Compared with respondents aged 15–24, all older age-groups had an elevated likelihood of infection (1.6–5.6). In addition, respondents who were married or cohabiting, as well as those separated or divorced, were more likely than those who had never married or cohabited to have an HSV-2 infection (1.7–2.6). Men who reported symptoms of genital ulcer disease in the past year and those who were not circumcised also had elevated odds of having HSV-2 (4.2 and 2.0, respectively), while women who had had two or more lifetime partners were more likely than those with fewer to test positive for the virus (2.6). Finally, both partners had genital herpes in 30% of the 2,708 couples tested for both HSV-2 and HIV; in 21%, only one partner was infected with HSV-2. In 10% of couples in which both partners had HSV-2, both partners also had HIV, compared with 3% of couples in which only one partner had HSV-2 and 0.4% of those in which neither partner had genital herpes.

The researchers believe their results support a clear relationship between HSV-2 and HIV infection. However, they noted several limitations of the study: its cross-sectional nature, which precluded determining the sequence of behaviors and infection; the possible underreporting of sexual activity and risk factors; and, in the absence of physical examinations, the possible misreporting of circumcision. Nonetheless, the authors assert that these findings can improve awareness of Kenya’s high HSV-2 prevalence, "help identify vulnerable groups … and opportunities to monitor and alter population risk for both HSV-2 and HIV, [and] advance our understanding of HSV-2 as a biologic cofactor in HIV acquisition and transmission."

–J. Thomas

REFERENCE

1. Mugo N et al., Prevalence of herpes simplex virus type 2 infection, human immunodeficiency virus/herpes simplex virus type 2 coinfection, and associated risk factors in a national, population-based survey in Kenya, Sexually Transmitted Diseases, 2011, 38(11):1059–1066.