Potential role of co-infections in causing higher community HIV-1 plasma RNA viral load (VL). Schematic diagram of the potential role of the high co-infection disease burden in sub-Saharan Africa (SSA) in increasing mean HIV-1 VL (diagram not to scale). At low co-infection prevalence, such as in resource-rich settings, the natural course of HIV-1 VL resembles that in yellow. In SSA, repeated co-infections resulting in bursts of viremia (in red), may lead, at the population level, to a higher mean HIV-1 VL over the course of HIV-1 infection, and greater aggregate person-time above the threshold HIV-1 VL for HIV-1 transmission. This figure is an adaptation from that in Cohen et al [38].