Men and women infected with HIV reduced the risk of transmitting the virus to their sexual partners by taking antiretrovirals, according to findings from a large-scale clinical study.

The clinical trial, known as HPTN 052, was scheduled to end in 2015 but the findings were released early (May 2011) as the result of a scheduled interim review of the study data by an independent data and safety monitoring board (DSMB). The DSMB concluded that it was clear that use of antiretrovirals by people living with HIV with relatively healthier immune systems substantially reduced transmission to their partners. The results are the first from a major randomised clinical trial to indicate that treating an HIV-infected individual can reduce the risk of sexual transmission of HIV to an uninfected partner.

The study included 1,763 HIV-serodiscordant couples, the vast majority of which (97%) were heterosexual. The study was conducted at 13 sites across Africa, Asia and the Americas. The HIV-positive partner was required to have a CD4 cell count between 350-550 at enrolment. Couples were randomly allocated to one of two groups:

in one group, the HIV-infected person immediately began taking antiretrovirals.

in the other group, the HIV-positive partner began antiretrovirals when his or her CD4 cell count fell below 250 cells/mm³ or if he/she developed an AIDS-related illness.

Among the 877 couples in the delayed treatment group, 27 HIV transmissions occurred. This was in contrast to only one (1) transmission that occurred in the immediate treatment group. This difference was statistically significant.

The viruses transmitted in these 28 cases were confirmed to be linked by genetic analysis, confirming that the source of the new infection was the HIV-positive partner.

This study only included a small number of gay men and MSM so it does not provide conclusive evidence related to HIV transmission where anal sex is the primary route of infection. However, anal sex is practised by heterosexual couples and in recent studies in Africa up to 10% of participants reported anal sex. (Anal sex rates among participants in this study have not yet been reported.)

There are two observational studies of HIV transmission in gay serodiscordant couples: one is an ongoing European study (the PARTNERS study). The other is the upcoming Australian study (to be conducted by the Kirby Institute). Both these studies focus on treatment, viral load and transmission.

More information at HPTN website