Why do young women have a much higher prevalence of HIV than young men? A study in Kisumu, Kenya and Ndola, Zambia.

OBJECTIVE: To examine the factors responsible for the disparity in HIV prevalence between young men and women in two urban populations in Africa with high HIV prevalence. DESIGN: Cross-sectional survey, aiming to include 1000 men and 1000 women aged 15-49 years in Kisumu, Kenya and Ndola, Zambia. METHODS: Participants were interviewed and tested for HIV and other sexually transmitted infections. Analyses compared the marital and non-marital partnership patterns in young men and women, and estimated the likelihood of having an HIV-infected partner. RESULTS: Overall, 26% of individuals in Kisumu and 28% in Ndola were HIV-positive. In both sites, HIV prevalence in women was six times that in men among sexually active 1 5-19 year olds, three times that in men among 20-24 year olds, and equal to that in men among 25-49 year olds. Age at sexual debut was similar in men and women, and men had more partners than women. Women married younger than men and marriage was a risk factor for HIV, but the disparity in HIV prevalence was present in both married and unmarried individuals. Women often had older partners, and men rarely had partners much older than themselves. Nevertheless, the estimated prevalence of HIV in the partners of unmarried men aged under 20 was as high as that for unmarried women. HIV prevalence was very high even among women reporting one lifetime partner and few episodes of sexual intercourse. CONCLUSIONS: Behavioural factors could not fully explain the discrepancy in HIV prevalence between men and women. Despite the tendency for women to have older partners, young men were at least as likely to encounter an HIV-infected partner as young women. It is likely that the greater susceptibility of women to HIV infection is an important factor both in explaining the male-female discrepancy in HIV prevalence and in driving the epidemic. Herpes simplex virus type 2 infection, which is more prevalent in young women than in young men, is probably one of the factors that increases women's susceptibility to HIV infection.