The role of heterosexual anal intercourse for HIV transmission in developing countries: are we ready to draw conclusions?

A recent meta-analysis suggested per-act HIV transmission probabilities of 1.7% (95% CI 0.3-8.9) for receptive AI and 0.08% (95% CI 0.06 to 0.11) for male-to-female VI from studies in developed countries, which roughly translates to a 20-fold increase in HIV risk per receptive AI act compared with receptive VI. 12 However, detailed data on the transmission probability of insertive AI are lacking. 13 Assuming that women engaging in AI have 8.2 unprotected sex acts over 3 months (with a HIV positive partner), 43% of which are receptive AI (as reported by the current study 1 ), then increases in per-act HIV transmission probability of AI compared with VI of five-, 10- and 20-fold translate into three-, five- and ninefold increases respectively in the 3-month cumulative risk of HIV acquisition, compared with the situation where all acts are VI (cumulative risk=0.0065)( fig 1A ).