• Hiam Chemaitelly, Susanne F Awad, and Laith J Abu-Raddad.
• Infectious Disease Epidemiology Group, Weill Cornell Medical College - Qatar, Cornell University, Qatar Foundation - Education City, Doha, Qatar.
• Epidemics. 2014 Mar 1; 6: 1-9.

BackgroundRepresentative and precise estimates for the annual risk of HIV transmission (ϕ) 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 ϕ 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 ϕ of 11.1 per 100 person-years across SSA. A clustering based on HIV population prevalence was observed with a median ϕ 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 ϕ, and suggested an increase of 0.95 per 100 person-years in ϕ 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.Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

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