Background:  Trichomonas vaginalis infection is one of the most common sexually transmitted infections worldwide. However, few adequately powered studies have addressed the question of whether trichomoniasis increases the risk of HIV-1 acquisition. The objective of the study presented here was to test this hypothesis using data from an 11-year study of female sex workers in Mombasa, Kenya.

Methods:  HIV-1-seronegative women were invited to enroll in a prospective cohort study to examine risk factors for HIV-1 acquisition. Participants were followed at monthly intervals. At enrollment and follow-up visits, women completed a standardized interview covering medical, gynecological, and sexual history. A physical examination was performed and blood and genital tract specimens were collected for diagnosis of HIV-1 and genital tract infections. We used Cox proportional hazards models to examine the association between trichomoniasis and HIV-1 acquisition.

Results:  Between 1993 and 2004, 1579 HIV-1-seronegative women were enrolled, of whom 1335 (84.5%) returned for at least 1 follow-up visit and were included in this analysis. These women accrued 3422 person-years of follow-up, with a median duration of 566 (interquartile range [IQR] 178 to 1330) days per woman. There were 806 cases of vaginal trichomoniasis (23.6 of 100 person-years), and 265 women seroconverted for HIV-1 (7.7/100 person-years). In univariate analysis, T. vaginalis infection was associated with a 1.60-fold increase in the risk of HIV-1 acquisition (95% confidence interval [CI] 1.11 to 2.31, p = 0.01). This association remained significant (hazard ratio [HR] 1.52, 95%CI 1.04 to 2.24, p = 0.03) after adjusting for demographic factors, sexual risk behavior, and incident genital tract infections.

Conclusions:  In this large, prospective cohort study, T. vaginalis infection was associated with a significant increase in the risk of HIV-1 acquisition. Given the high global prevalence of trichomoniasis, this infection could account for a high population attributable risk percentage for HIV-1 acquisition. Interventions to reduce the prevalence of T. vaginalis infection should be evaluated as a potentially important HIV-1 prevention strategy.