The risk of HIV transmission within HIV-1 sero-discordant couples appears to vary across sub-Saharan Africa

• We estimated the annual risk of HIV transmission in HIV sero-discordant couples (ϕϕ).
• The median ϕϕ was at 11.1 per 100 person-years across sub-Saharan Africa.
• ϕϕ was higher in high compared to low HIV prevalence countries.

BackgroundRepresentative and precise estimates for the annual risk of HIV transmission (ϕϕ) from the infected to the uninfected partner in a stable HIV-1 sero-discordant couple (SDC) are not available. Nevertheless, quantifying HIV infectiousness is critical to understanding HIV epidemiology and implementing prevention programs.Materials and methodsWe estimated ϕϕ and examined its variation across 23 countries in sub-Saharan Africa (SSA) by constructing and analyzing a mathematical model that describes HIV dynamics among SDCs. The model was parameterized using empirical measures such as those of the nationally representative Demographic and Health Surveys. Uncertainty and sensitivity analyses were conducted to assess the robustness of the findings.ResultsWe estimated a median ϕϕ of 11.1 per 100 person-years across SSA. A clustering based on HIV population prevalence was observed with a median ϕϕ of 7.5 per 100 person-years in low HIV prevalence countries (<5%) compared to 19.5 per 100 person-years in high prevalence countries (>5%). The association with HIV prevalence explained 67% of the variation in ϕϕ, and suggested an increase of 0.95 per 100 person-years in ϕϕ for every 1% increase in HIV prevalence.ConclusionsEmpirical measures from cohort studies appear to underestimate HIV infectiousness in SSA. The risk of HIV transmission among SDCs appears also to vary across SSA, and this may have contributed to the contrasting HIV epidemic trajectories in this continent.