Only a fraction of new HIV infections occur within identifiable stable discordant couples in sub-Saharan Africa

To estimate the contribution of HIV-1 sero-conversions among stable HIV sero-discordant couples (SDCs) to total HIV population-level incidence in sub-Saharan Africa. We constructed a mathematical model, grounded in nationally representative demographic and epidemiological data, that estimates the annual number of HIV-1 transmissions from the infected partners to the uninfected partners among established SDCs, and compares its value to an estimate for the overall HIV population-level incidence in 20 countries in sub-Saharan Africa. We defined identifiable HIV-1 transmissions among SDCs as those that a hypothetical screening and intervention program would have the potential to avert. Uncertainty and sensitivity analyses were incorporated to assess the robustness of the findings. Across the 20 countries, an average of 29% (range: 10-52%) of new HIV-1 infections occurred in which one partner in an identifiable SDC infected the other. The percentage of total HIV new infections in a country that occurred within such identifiable SDCs tended to be lower in countries with larger general population HIV epidemics. For most countries, HIV-1 incidence among SDCs is unlikely to exceed 50% of new HIV infections in the whole population. Only a fraction of HIV-1 heterosexual transmissions occur within identifiable SDCs. Prevention within SDCs at scale requires a series of potentially challenging programmatic requirements to be met. Despite the importance of prevention programs aiming at protecting the sero-negative partner in an SDC, a wider strategy utilizing the full range of prevention modalities, which would limit the original generation of SDCs, is also needed.