The HIV/AIDS epidemic is now in its thirtieth year. Over the past decade remarkable progress in addressing the consequences of HIV has been made, with nearly five million people on anti-retroviral treatment. However, prevention efforts have been less successful: globally there are approximately 7,000 infections daily, with the numbers of newly infected outnumbering those newly being put on treatment. Sub-Saharan Africa continues to bear the brunt of the HIV epidemic, with HIV prevalence rates of up to 26 percent in some countries (UNAIDS 2010a). Despite these challenges, there are also marked successes, with declines in rates of new HIV infections in many regions globally, including in sub-Saharan Africa. These declines are likely to be the result of large-scale HIV prevention efforts, as well as more fundamental changes in sexual behavior that have evolved as communities respond to the realities of the HIV epidemic and the toll that it is taking.

In sub-Saharan Africa, HIV transmission is largely heterosexual, although the role of transmission among men who have sex with men, and among injecting drug users, is also starting to be acknowledged. Established responses to addressing the heterosexual transmission of HIV include behavioral change communication programs, interventions focused on key at-risk populations (such as sex workers and their clients), male circumcision, HIV testing and counseling, condom promotion, and the treatment of sexually transmitted infections. Some of these interventions have been considered in other RethinkHIV papers, and are likely to remain central to a comprehensive HIV response. Although RethinkHIV focuses on sub-Saharan Africa in its entirety, the epidemic varies considerably by setting. In practice the optimal mix of interventions implemented in any setting will vary, and be influenced by the extent to which, at a population level, HIV infection is largely concentrated amongst vulnerable groups such as sex workers, men who have sex with men, or injecting drug users (a concentrated HIV epidemic), or more widely generalized in the population (a generalized HIV epidemic).