Researchers analyzed data from a study of heterosexual HIV-discordant couples in Africa to assess HIV transmission per sexual encounter. They found that of 3297 couples, the unadjusted per-act risks of unprotected male-to-female (MTF) and female-to-male (FTM) transmission were 0.0019 and 0.0010, respectively. The researchers also found that reported condom use decreased per-act risk of transmission by 78%.
This study adds to the existing pool of recent research that demonstrates the very low risk of transmission per sexual encounter for women who have sex with men (WSM) and men who have sex with women (MSW). It also lends additional support to extensive data on the efficacy of condom use in dramatically reducing the risk of transmitting HIV.