Non-ulcerative sexually transmitted diseases as risk factors for HIV-1 transmission in women: results from a cohort study

Abstract

Objectives: The heterosexual spread of HIV-1 is occurring at different rates in different parts of the world. The transmission probability of HIV-1 per sexual contact is low, but may be greatly enhanced by several cofactors. Sexually transmitted diseases (STD), especially genital ulcers, may be such factors. So far, epidemiological evidence that other STD facilitate HIV-1 transmission is weak. The objective of this study was to determine whether treatable STD enhanced sexual transmission of HIV-1 in a cohort of female prostitutes in Kinshasa, Zaire.

Methods: We conducted a nested case-control study of 431 initially HIV-1-negative women followed prospectively for a mean duration of 2 years (with monthly STD check-ups and 3-monthly HIV-1 serology). Cases (seroconverters, n = 68) were compared with controls (women who remained HIV-1-negative, n = 126) for incidence of STD and sexual exposure during the presumed period of HIV-1 acquisition.

Results: The annual incidence of HIV-1 in this cohort was 9.8%. Seroconverters were younger than HIV-1-negative women (mean age, 24.6 versus 26.8 years; P = 0.04). During the period of HIV-1 acquisition, cases had a much higher incidence of gonorrhoea, chlamydial infection and trichomoniasis, and engaged in unprotected sex with clients and partners more frequently than controls. After controlling for sexual exposure by multivariate analysis, adjusted odds ratios for seroconversion were 4.8 [95% confidence interval (CI), 2.4-9.8] for gonorrhoea, 3.6 (95% CI, 1.4-9.1) for chlamydial infection and 1.9 (95% CI, 0.9-4.1) for trichomoniasis. Genital ulcers were more frequent in cases than controls, but much less common than other STD.

Conclusion: Non-ulcerative STD were risk factors for sexual transmission of HIV-1 in women, after controlling for sexual exposure. Because of their high prevalence in some populations, non-ulcerative STD may represent a considerable population-attributable risk in the transmission of HIV-1 worldwide. The identification of treatable STD as risk factors for HIV-1 transmission offers an important additional strategy for the prevention of HIV/AIDS.

PIP: There is only a small probability that HIV-1 will be transmitted via any single sexual contact. The risk of transmission, however, during such an act may be greatly increased by the presence of ulcerative genital sexually transmitted disease (STD). Little evidence is published on whether infection with non-ulcerative STD facilitates the transmission of HIV-1. The authors therefore investigated whether treatable STD enhanced the sexual transmission of HIV-1 in a cohort of female prostitutes in Kinshasa, Zaire. 431 initially HIV-1-seronegative women were followed prospectively in this nested case-control study for a mean duration of two years in monthly STD check-ups and three-monthly HIV-1 serology. The 68 women who seroconverted were compared against the 126 women who remained HIV-1-seronegative for the incidence of STD and sexual exposure during the presumed period of HIV-1 acquisition. There was a 9.8% annual incidence of HIV-1 in this cohort of subjects. Seroconverters were of mean age 24.6 years compared to 26.8 years for the HIV-seronegative women. During the period of HIV-1 acquisition, cases had a much higher incidence of gonorrhea, chlamydial infection, and trichomoniasis, and engaged in unprotected sex with clients and partners more frequently than controls. After controlling for sexual exposure by multivariate analysis, adjusted odds ratio for seroconversion were 4.8 for gonorrhea, 3.6 for chlamydial infection, and 1.9 for trichomoniasis. Genital ulcers were more frequent in cases than controls, but much less common than other STD. These findings therefore suggest that non-ulcerative STDs were risk factors for the sexual transmission of HIV-1 in these women. Such STD may be a considerable population-attributable risk in the transmission of HIV-1 worldwide given the high prevalence of non-ulcerative STDs in some populations.