Running on empty: sexual co-factors are insufficient to fuel Africa's turbocharged HIV epidemic.

The hypothesis that heterosexual transmission drives sub-Saharan Africa's HIV epidemics requires much faster transmission dynamics in Africa than in the US and Europe, where heterosexual transmission is arguably insufficient to maintain existing levels of HIV prevalence. Initially, experts surmised that Africans had more sexual partners; however, studies of sexual behaviour circa 1990 undermined this assumption. Next, it was supposed that the high burden of bacterial sexually transmitted disease (STD) in Africa explained greater HIV transmission efficiency; however, during the 1990s, community studies in Africa showed that STD had much less than expected impact on HIV transmission. Current attempts to explain HIV as a primarily sexual epidemic in Africa propose multiple factors, including herpes simplex virus type 2, lack of male circumcision, concurrency, and others. These factors also fail for various reasons to account for Africa's HIV epidemics: they are present also in the US and/or Europe; they do not correlate with differences in HIV prevalence across Africa; etc. While behavioural and biological variables influence personal risk for HIV acquisition, the available evidence suggests that they do not differentiate African from US and European epidemics, nor do they determine the differential HIV epidemic trajectories noted across Africa.