Using oral contraceptives or the hormonal injectable significantly affects a woman's risk of acquiring certain sexually transmitted diseases (STDs), according to data from a cohort of Kenyan female sex workers.¹ Compared with women who do not practice contraception, those who rely on oral contraceptives are more likely to acquire chlamydia or vaginal candidiasis, but are less likely to acquire bacterial vaginosis. Women who use the injectable also are more likely than women not practicing contraception to acquire chlamydia, but are less likely to acquire trichomoniasis or bacterial vaginosis or to be diagnosed with pelvic inflammatory disease. Consistent use of condoms significantly reduces the risk of gonorrhea, chlamydia, genital ulcer disease, bacterial vaginosis, cervical mucopus, cervicitis and pelvic inflammatory disease.

To investigate whether using oral contraceptive pills or the injectable affects the risk of STD infection, researchers conducted a prospective study among sex workers in Mombasa between February 1993 and August 1999. After responding to a questionnaire about recent sexual activity and contraceptive use, participants were given a physical examination that included STD screening. The women returned for monthly visits, at which time they completed follow-up questionnaires and were screened for STDs. Multivariate analyses of the data were adjusted for age, years of education, years as a sex worker, parity, number of sexual partners, number of sexual contacts and condom use.

On average, the women were 26 years old, had sex twice per week, had one partner per week and had been a sex worker for one year. Sixty-five percent reported using no hormonal contraceptive method, 18% used the injectable, 16% used oral contraceptive pills and 2% reported using other hormonal methods; 63% used condoms for all sex acts. At the initial screening, 39% of the women had bacterial vaginosis, 21% cervicitis, 20% vaginal discharge and 14% candidiasis. Over the study period, 158 of the 948 women included in the analyses became infected with HIV.

At enrollment, 213 women reported relying on oral contraceptives, while 251 said that they used the hormonal injectable. Compared with women who did not practice contraception or had been sterilized, a significantly smaller proportion of the women who used the injectable had sex more than twice a week (34% vs. 22%) or had more than one partner per week (43% vs. 30%).

Use of oral contraceptives was associated with a significantly increased risk of chlamydia (hazard ratio, 1.8), vaginal candidiasis (1.5), cervical mucopus (1.7) and cervicitis (1.8), and a decreased risk of bacterial vaginosis (0.8). Women who used the hormonal injectable had significantly elevated risks of chlamydia (1.6), cervical mucopus and cervicitis (1.5 each), and significantly decreased risks of trichomoniasis (0.6), bacterial vaginosis (0.7), vaginal discharge (0.8) and pelvic inflammatory disease (0.4). Consistent use of condoms was associated with significantly decreased risks of gonorrhea (0.6), chlamydia (0.6), genital ulcer disease (0.5), bacterial vaginosis (0.9), cervical mucopus (0.6), cervicitis (0.8) and pelvic inflammatory disease (0.6).

A link between hormonal contraception and cervical infections is biologically plausible, according to the researchers, because estrogen and progesterone can enhance or suppress the growth and persistence of vaginal flora. They note that the "most important implications of our study findings concern the potential for hormonal contraceptive use to influence transmission of HIV-1 infection by increasing or decreasing susceptibility to STDs." Because their study population consisted of female sex workers who were at an elevated risk of exposure to STDs, the researchers suggest that "further studies in low-risk populations are needed to assess the generalizability of our results."--J. Rosenberg

REFERENCE

1. Baeten J et al., Hormonal contraception and risk of sexually transmitted disease acquisition: results from a prospective study, American Journal of Obstetrics and Gynecology, 2001, 185(2):380-385.