Combined antiretroviral treatment and heterosexual transmission of HIV-1: cross sectional and prospective cohort study.

Objective: To estimate the risk and probability of heterosexual transmission of HIV-1 from infected people taking combined antiretroviral treatment.

Design: Cross sectional and prospective cohort studies.

Setting: HIV clinic in Madrid, Spain.

Participants: Stable heterosexual couples with one partner with HIV-1 infection (index partner) and the other reporting this sexual relationship as the only risk exposure.

Main Outcome Measures: HIV seroprevalence in non-index partners at enrolment and seroconversions in follow-up according to antiretroviral treatment taken by the index partner.

Results: In 476 couples in which the index partner was not taking antiretroviral treatment, HIV seroprevalence at enrolment in non-index partners was 9.2% (n=44), whereas in 149 couples in which the index partner was taking combined antiretroviral therapy no partner was infected (P<0.001). During follow-up, the 341 serodiscordant couples in which the index partner was not taking antiretroviral treatment had about 11 000 acts of intercourse without condoms, 50 natural pregnancies, and five HIV seroconversions (0.0004 per unprotected intercourse; 95% confidence interval 0.0001 to 0.0010); 294 of these couples always used condoms, accounting for about 42 000 acts of intercourse, 136 risk exposures from condom failure, and one HIV seroconversion. The relative risk associated with condom use was 0.07 (0.01 to 0.58). In 144 couples the index partner was taking combined antiretroviral treatment; they accounted for over 7000 unprotected acts of intercourse and 47 natural pregnancies but no HIV seroconversion (0 to 0.0005 per unprotected intercourse).

Conclusions: The heterosexual infectivity of HIV-1 in individuals taking effective antiretroviral treatment is low. Avoidance of unprotected intercourse and receipt of antiretroviral treatment by the infected partner in accordance with protocols are complementary measures to prevent HIV transmission.