Infection with HIV increases the risk of acquiring other STIs, according to a 10-year prospective study conducted among female sex workers in Kenya.¹ Risks of candidiasis, gonorrhea and genital ulcer disease were significantly higher among HIV-positive women than among HIV-negative women (hazard ratios, 1.5-2.8); the risks of candidiasis and genital ulcer disease rose with increasing levels of immunosuppression.

The prospective cohort study followed 1,215 female sex workers who visited a municipal health clinic in Mombasa, Kenya, from 1993 to 2003. Participants, who had to be HIV-negative, were interviewed for their medical, gynecologic and sexual history. At monthly follow-up visits, they provided data on sexual behavior, contraceptive use and any genital symptoms during the previous month. At each visit, the women were examined and tested for HIV and other STIs, including syphilis, gonorrhea, chlamydia, vulvovaginal candidiasis, bacterial vaginosis and trichomoniasis; the presence of genital ulcer disease (defined as epithelial disruption of the cervix, vagina or vulva) was also assessed.

During the course of the study, 238 of the participating sex workers contracted HIV. Beginning in 1998, the CD4 cell counts of infected participants were measured every three months to monitor the level of immuno-suppression.

Proportional hazard models were used to compare the risk of genital tract infections in HIV-positive and HIV-negative women. Models controlled for education, number of children, workplace, douching practices, age, duration of prostitution, number of sex partners, frequency of sex, condom and contraceptive use, and time since last clinic visit. Visits at which women were pregnant were excluded from analysis. To assess how immunosuppression affected STI susceptibility, the study compared STI risk among women with CD4 cell counts of fewer than 200, 200-499 and 500 or more per mcl.

Study participants had a median age of 26 years (range, 22-31), and had a median of eight years of education; their median time as sex workers was one year. Seventy-five percent worked in a bar. The median frequency of sexual activity was two times per week, with one sex partner each week. Sixty-two percent of the women reported always using a condom; 71% douched with soap. About one-third used a hormonal method of birth control, including 20% who relied on the injectable and 14% who used oral contraceptives. The median duration of participant follow-up was 617 days and the time between visits was 35 days.

Compared with HIV-negative sex workers, sex workers who were HIV-positive had significantly increased risks of having genital ulcer disease (hazard ratio, 2.8), gonorrhea (1.6) and vulvovaginal candidiasis (1.5).

The risk of some STIs was associated with declining CD4 cell counts in HIV-positive women. For genital ulcer disease, the hazard ratio rose from 2.5 for women who had a CD4 count of at least 500 cells/mcl to 5.0 for those who had fewer than 200 cells/mcl. For candidiasis, the hazard ratio increased from 0.9 to 2.1. Under a definition of candidiasis that relies on women reporting vaginal itching or discharge when they were specifically asked whether they had these symptoms, the hazard ratio increased to 5.4 for the highest level of immunosuppression.

Condom use also exerted a significant effect on the incidence of genital tract infections in this population. When compared with women who reported using condoms less than 100% of the time, those who always used condoms were at lower risk of gonorrhea (hazard ratio, 0.6), chlamydia (0.6), genital ulcer disease (0.7), cervical mucopus (0.8) and bacterial vaginosis (0.9).

According to the authors, their results provide strong evidence of epidemiological synergy between HIV and genital tract infections in this sample of female sex workers. They note the study's strengths - its large cohort, long follow-up period, high incidence of genital tract infections, repeated screening of participants and long-term monitoring of sexual activity. Nevertheless, they also point out several limitations of the research - possible underreporting of risky sexual behavior that may increase women's exposure to STIs, failure to evaluate the role of sex partners and networks among the sex workers, use of the less sensitive culture method to detect gonorrhea and the fact that genital ulcer disease encompasses a variety of etiologies.

It is still unknown, the authors say, whether HIV infection influences the duration, severity or recurrence of genital tract infections. Because of the prevalence of such infections among HIV-positive women, they recommend "more intensive treatment and prevention of these conditions as a means of decreasing HIV-1 infectivity."

-J. Thomas

REFERENCE

1. McClelland RS et al., Contribution of HIV-1 infection to acquisition of sexually transmitted disease: a 10-year prospective study, Journal of Infectious Diseases, 2005, 191(3):333-338.