Background: Young women in sub-Saharan Africa are at very high risk of HIV acquisition, and high prevalence levels have been observed among women reporting one lifetime partner and few sexual contacts. Such findings have led to hypotheses that the probability of HIV transmission from men to women must be far higher than previously appreciated.
Methods: We used the data from a cross-sectional national household survey of HIV among South African women aged 15-24 years to estimate the per-partnership transmission probability from men to women. Estimates were obtained using maximum likelihood methods and a transmission probability model allowing for random error in the self-reported number of lifetime partners. Sensitivity analyses were employed to assess the robustness of the per-partnership transmission probability estimates to the assumed HIV prevalence in male partners.
Results: HIV prevalence in women was 21.2% (95% confidence interval 17.9-24.5). The mean reported number of lifetime partners was 2.3. A significant increase in prevalence was observed with increasing lifetime partner numbers (P = 0.02). For a range of plausible values of the partner prevalence, the estimated per-partnership transmission probability varied from 0.74 to 1.00 with 95% confidence intervals ranging from 0.56 to 1.00.
Discussion: The per-partnership probability of HIV transmission from men to women in this population was very high. Before this, the majority of studies examining per-partnership transmission probabilities estimated values below 50%. Identifying the factors that may drive the efficient spread of HIV in sub-Saharan Africa is essential for the development of effective prevention interventions.