oa Estimating HIV Incidence Rate among Stable Sexual Partnerships in Sub-Saharan Africa

Background: Empirical evidence suggests that HIV incidence rate within stable discordant sexual partnerships in sub-Saharan Africa (SSA) varies between 1.2 and 19.0 per 100 person-years. Estimating HIV incidence rate within stable discordant partnerships is critical for determining the contribution of HIV sero-conversions among these partnerships to total HIV incidence.

Objective: To estimate HIV incidence rate within stable discordant partnerships using nationally representative data and explore potential underlying factors contributing to their variability across a range of epidemic settings in SSA.

Methods: We constructed a mathematical model based on competing-hazards formalism to estimate HIV incidence rate within stable discordant partnerships across 20 countries in SSA. We also used the model to analyze the patterns of HIV discordancy in SSA. The model was parameterized using Demographic Health Survey data and analyses were conducted at endemic equilibrium. Sensitivity analyses were performed to explore the dependence on the dynamical drivers of discordancy.

Results: Our model fitted well the empirical epidemiological measures of HIV discordancy and yielded an estimate for HIV incidence rate among discordant partnerships of 14.7 per 100 person-years (95% CI 9.9–19.4 per 100 person-years). HIV incidence rate ranged between 3.9 and 34.9 per 100 person-years across the countries. We also identified HIV incidence rate within stable discordant partnerships and HIV incidence rate from sources external to the partnership (or equivalently HIV prevalence) as key determinants of the variability in discordancy measures across SSA.

Conclusions: Our estimate for the HIV incidence rate among discordant partnerships agrees well with empirical estimates for this measure. There is however considerable variability across the countries. Biological and behavioral factors including differences in transmission rates such as due to male circumcision, may have contributed to the variability in HIV incidence rates among discordant partnerships across SSA. More research is needed to elucidate the determinants of this variability in incidence rates.