Sexually transmitted infections (STIs) are an important cause of morbidity, especially among African women, whose access to timely diagnosis and treatment is often deficient.^1–4 Adverse sequelae include poor birth outcomes, neonatal and infant infections, ectopic pregnancy, anogenital cancer, infertility, pelvic inflammatory disease, and death.^5–8 In addition, many STIs, in particular herpes simplex virus type 2 (HSV-2), facilitate transmission of human immunodeficiency virus (HIV).^9–15

There are multiple correlates for the acquisition of different STIs, including demographic, behavioural, and biological considerations. With the exception of HSV-2, lower age has been shown to be a risk factor for the acquisition of STIs; younger people are at higher risk of acquiring STIs than are adults.^16–18 Gender and education have been found to be significant factors in STI acquisition. Kenyan women have a higher prevalence of HSV-2 than do men,¹⁹ and a study in Tanzania found that educated women are less likely to be infected with syphilis compared to their uneducated counterparts.²⁰ Number of sexual partners has also been found to be a risk factor, with sexual concurrency²¹ and sexual networks²² analyses showing that an increasing number of sexual partners is associated with an increased risk of STI acquisition. HIV infection increases the chances of acquiring various STIs and vice versa. A study in Ethiopia found that HIV co-infection predisposes women to getting more ulcerative STIs, especially HSV-2, as well as to failing STI treatment.²⁷

In January 2007, Kenya Medical Research Centre (KEMRI)/Centers for Disease Control and prevention (CDC) initiated an HIV incidence cohort study to prepare for future community-based HIV vaccine or other prevention trials among young adults in Kisumu. The purpose of this analysis was to use data from the screening visit for this cohort to determine: (1) overall prevalence of four STIs: syphilis, gonorrhoea, HSV-2, and chlamydia and (2) demographic and behavioural correlates of prevalent STIs.

Our data show that more than a third of screened participants for an HIV incidence cohort study in periurban Kisumu, western Kenya, had at least one STI (syphilis, gonorrhoea, HSV-2, and/or chlamydia). These results are consistent with what was seen in two studies previously done in the study area.^19,30 Several factors were associated with having an STI, including female gender, low education level, unprotected sex with a main partner, being divorced/widowed/separated or married, and being HIV-infected.

Women accounted for most (75.7%) STI infections, which is consistent with findings from other studies conducted in the same general geographical location, including the four cities study,³⁰ the Asembo baseline cross-sectional HIV survey,³¹ and the Kenya Demographic and Health and Kenya AIDS Indicator Surveys.^19,32 The 10-fold prevalence of HSV-2 infection compared to other STIs is consistent with the known epidemiology in many regions of the world.

Overall, the odds of having one or more STI were six times as great for women as circumcised men. The odds were 1.2 times as great for uncircumcised men as for circumcised men even though this was not significant; suggesting, as has been reported in other studies,^20,33 that circumcision is protective for STIs in men. Even when the STIs were segregated by acuteness, the odds were still greater in women with women having four times and five times greater odds than their circumcised male counterparts. Not unexpectedly, unprotected sex with a main partner was also associated with having an STI.^25,26,34 This, however, was not true with having an acute STI. Other studies have shown that women in this and other societies are often in a subordinate position and may lack the power to make decisions about condom use,^35–40 and that despite the provision of condoms and risk-reduction counselling, unprotected sex out of marriages continues.^41,42

Our analysis also documents that having low education and being divorced, widowed, or separated are important correlates for having a chronic STI. Studies have shown that having increased education is associated with more knowledge, safer sexual behaviours, and lower HIV infection rates to the extent that education has been called the “social vaccine.”⁴¹ Our data suggests that marital status was associated with higher odds of having an STI for divorced/widowed or separated individuals, most of whom were women. This may be related to previous reports that divorce for women is a risk factor for being involved in commercial sex work and the starting of other relationships.^42–44 Divorced, widowed, or separated women may have pressing financial obligations, including dependent children, and few skills to earn money, thus they resort to some type of transactional sex, including sex work.

We found that HIV-positive individuals had more than four times the odds of having a chronic STI. Several other studies have also shown that a relationship exists between HIV infection and STIs.^23,27,34,45 A study in Ethiopia found that HIV co-infection predisposes women to developing more frequent ulcerative STIs, especially HSV-2, as well as to failing STI treatment. ²⁷ These findings were also seen in another study in Tanzania that enrolled high-risk women which are consistent with what was seen in this study.³⁴ Behavioural interventions to prevent HIV have been shown to also work to prevent most STIs.^13,46–49 Biomedical interventions to prevent HIV such as tenofovir vaginal gel microbicide have been shown to have the potential to also prevent HSV-2 infection and, thus, may be especially helpful in impacting the HIV epidemic in sub Saharan Africa.^50–52

Even though several studies have shown anal sex to be a risk factor for prevalent and incident STIs,^53–58 we found the odds of having chronic STIs lower among participants who reported anal sex compared to those who did not. This may be due to the fact that we did not screen for any rectal STIs. We also found the odds of having STIs to be lower in those using recreational drugs contrary to what most studies have reported.^59–61 Reported recreational drug use was rare in our study population, which might reflect the lower availability of recreational drugs in inland western Kenya than at the coast and urban slums in Nairobi,^62–64 and we therefore feel that this finding in our analysis might reflect a spurious association due to low numbers.

Several limitations should be considered in the interpretation of our findings. First, our participants may not be representative of the Kisumu population as they were volunteers for a research study and were recruited through convenience sampling. However, the screening HIV prevalence we found is nearly identical to local population estimates from national surveillance data,¹⁹ suggesting that perhaps the study participants may be representative of the local community regardless of the convenience sampling and potential bias of desiring to participate in a research study. Second, there may be response bias as with any self-reported behavioural/risk data collection, although we believe use of ACASI facilitated more truthful responding^65,66 than face-to-face interviews would have. Thirdly, our diagnosis of chlamydia/gonorrhoea was an assay for active disease, but for HSV-2 and syphilis was serology, which may have missed recent acquisition and which also classifies people as positive even if their infection was remote and is inactive. We also did not test for any rectal STIs and so could not correlate this to anal sex. Lastly, because this was a cross-sectional study evaluating prevalence of STI and HIV within a prospective study, we cannot determine timing or causality. The strength of our analysis, however, is that we were able to collect and correlate both behavioural and biological correlates of prevalent STI.

In conclusion, similar to HIV infection in Kenya, STI prevalence is high in this part of Kenya, with women more likely to be infected than men in our research setting. Multiple strategies are needed to address the overall high prevalence of STIs as well as the gender disparity. In addition to increasing screening and access to health care,⁶⁷ and developing women-controlled biomedical interventions like vaginal microbides, ⁶⁸ non-medical methods should be employed to reduce the gender disparity in HIV and STIs. Because HIV can be considered an STI (although it was considered separately in this analysis), the structural methods which may have an impact are virtually the same as for HIV, and would include focusing on education, about which the WHO has stated that, “…a good basic education ranks among the most effective-and cost-effective-means of HIV prevention.”⁶⁹ In conjunction with education, reducing early marriage is another important strategy, as the husbands of married adolescents and young adult women are more likely to be HIV-positive compared to the male partners of single woman.^31,70 Finally, empowerment of adolescent girls and women through structural and economic interventions has been effectively used to improve their health.^3,71 By using multiple strategies (biomedical, socio-economic, and cultural), STI and HIV prevalence in Kenya could be reduced.