The risk of sexually transmitted HIV was reduced by 96% when the infected partner received a combination of three or more antiretroviral drugs, according to the findings of an international study involving 1,763 serodiscordant couples.
The results "are the first from a major randomized trial to indicate that treating an HIV-infected individual can reduce the risk of sexual transmission of HIV to an uninfected partner," according to a statement issued by the National Institute of Allergy and Infectious Diseases (NIAID), which sponsored the study.
Previous studies on the ability of antiretrovirals to prevent sexual transmission of HIV were either observational and epidemiologic.
Results from the current randomized study were so striking that the trial, which began in April 2005 and was slated to continue into 2015, was halted early. The study has not yet been published; the results were reported in the NIAID statement.
"This new finding convincingly demonstrates that treating the infected individual – and doing so sooner rather than later – can have a major impact on reducing HIV transmission," NIAID director Dr. Anthony Fauci said in the statement.
The study enrolled 1,763 mostly heterosexual serodiscordant couples aged 18 years and older in several African countries, Brazil, India, Thailand, and the United States. The HIV-infected partners were randomly assigned to either immediately start triple or quadruple antiretroviral therapy, or to a deferred-treatment group that started therapy only after their CD4 counts dropped below 250 cells/mm3, or they developed pneumocystis pneumonia, or another AIDS-related event. All couples received information and counseling about safe sex and were treated for any HIV-related complications.
There were 39 previously uninfected partners who became infected with HIV; genetic analyses of the viruses in both partners determined that 28 of these individuals were infected from their HIV-infected partners, 7 were infected by another sexual partner, and the results of the remaining 4 have not yet been determined.
Of the 28 cases that were determined to be from the sexual partner in the study, 27 were among the 877 serodiscordant couples in the deferred-treatment group; only one case occurred among those in the immediate-treatment group. This highly significant difference corresponded to a 96% risk reduction attributed to immediate therapy, and spurred the independent data and safety monitoring board’s recommendation that the deferred-treatment arm be stopped early.
In addition to evaluating the impact of antiretroviral therapy on sexual transmission of HIV, the investigators looked at whether immediate treatment altered the course of disease in the HIV-infected individuals. Among the HIV-infected partners in the deferred-treatment group, there were 17 cases of extrapulmonary tuberculosis, compared with 3 cases among the infected partners in the immediate-treatment group, a significant difference. The number of deaths, however, was not significantly different: Ten deaths occurred in the immediate-treatment group versus 13 in the deferred-treatment group.
The study was conducted by the HIV Prevention Trials Network, largely funded by NIAID, and also received funding from the National Institute on Drug Abuse and the National Institute of Mental Health; the AIDS Clinical Trials Group, funded by NIAID, also provided support for the study. The 11 antiretroviral drugs used in various combinations in the in the study were provided by the manufacturers, Abbott Laboratories; Boehringer Ingelheim Pharmaceuticals; Bristol-Myers Squibb; Gilead Sciences; GlaxoSmithKline/ViiV Healthcare; and Merck.