Findings from the Partners in Prevention study, presented at CROI (abstract 136) and published in the May 27, 2010, advance issue of The Lancet, indicate that starting combination ART early can reduce the risk of HIV transmission between partners in heterosexual couples. The trial (which was designed to assess whether treating genital herpes could reduce HIV transmission) included more than 3,000 serodiscordant (one positive, one negative) couples in seven sub-Saharan countries.
At study entry, participants had CD4 cell counts above 250 cells/mm3 and were not on ART. During two years of follow-up, 349 HIV positive participants (10%) started ART, half with a CD4 count below 200 cells/mm3, one-third with 200-349 cells/mm3, and 15% with 350 cells/mm3 or higher (including pregnant women receiving antiretroviral drugs to prevent perinatal HIV transmission).
A total of 151 new infections occurred, of which 103 were verified as transmissions within a couple with known ART status, not including perinatal prevention. Of these transmission cases, 102 were from HIV positive participants not taking ART (an incidence rate of 2.24 per 100 person-years). In the absence of treatment, the likelihood of transmission increased as the positive partner's CD4 count decreased (from 8.79 per 100 person-years below 200 cells/mm3 to 1.82 per 100 person-years above 500 cells/mm3).
One transmission, however, was from a person receiving therapy (0.37 per 100 person-years). While ART reduced the risk of transmission by 92%, this single infection demonstrates that treatment does not completely eliminate risk.
Liz Highleyman (firstname.lastname@example.org) is a freelance medical writer based in San Francisco.