Extra-couple HIV transmission in Sub-Saharan Africa: A mathematical modelling study of survey data. The Lancet 6736(12

Background The proportion of heterosexual HIV transmission in sub-Saharan Africa that occurs within cohabiting partnerships, compared with that in single people or extra-couple relationships, is widely debated. We estimated the proportional contribution of diff erent routes of transmission to new HIV infections. As plans to use antiretroviral drugs as a strategy for population-level prevention progress, understanding the importance of diff erent transmission routes is crucial to target intervention eff orts. Methods We built a mechanistic model of HIV transmission with data from Demographic and Health Surveys (DHS) for 2003–2011, of 27 201 cohabiting couples (men aged 15–59 years and women aged 15–49 years) from 18 sub-Saharan African countries with information about relationship duration, age at sexual debut, and HIV serostatus. We combined this model with estimates of HIV survival times and country-specifi c estimates of HIV prevalence and coverage of antiretroviral therapy (ART). We then estimated the proportion of recorded infections in surveyed cohabiting couples that occurred before couple formation, between couple members, and because of extra-couple intercourse. Findings In surveyed couples, we estimated that extra-couple transmission accounted for 27–61 % of all HIV infections in men and 21–51 % of all those in women, with ranges showing intercountry variation. We estimated that in 2011, extra-couple transmission accounted for 32–65 % of new incident HIV infections in men in cohabiting couples, an