Incidence of HIV infection in stable sexual partnerships: A retrospective cohort study of 1802 couples in Mwanza region Tanzania.

The objective was to describe the dynamics of HIV transmission in stable sexual partnerships in rural Tanzania. The design used was a retrospective cohort study nested within community-randomized trial to investigate the impact of a sexually transmitted disease treatment program. A cohort of 1802 couples was followed up for 2 years with the HIV status of each couple assessed at baseline and follow-up. At baseline 96.7% of couples were concordant-negative 0.9% were concordant-positive 1.2% were discordant with the male partner being HIV-positive and 1.2% were discordant with the female partner being HIV-positive. Individuals living with an HIV-positive partner were more likely to be HIV-positive at baseline (women: odds ratio [OR] = 75.7 95% confidence interval [CI]: 33.4-172; men: OR = 62.4 CI: 28.5-137). Seroincidence rates in discordant couples were 10 per 100 person-years (py) and 5 per 100 py for women and men respectively (rate ratio [RR] = 2.0 CI: 0.28-22.1). In concordant-negative couples seroincidence rates were 0.17 per 100 py in women and 0.45 per 100 py in men (RR = 0.38 CI: 0.12-1.04). Individuals living in discordant couples were at a greatly increased risk of infection compared with individuals in concordant-negative couples (RR = 57.9 CI: 12.0-244 for women; RR = 11.0 CI: 1.2-47.5 for men). Men were more likely than women to introduce HIV infection in concordant-negative partnerships. In discordant couples incidence in HIV-negative women was twice as high as in men. HIV-negative individuals in discordant partnerships are at high risk of infection and preventive interventions targeted at such individuals are urgently needed. (authors)