People with HIV who take antiretroviral drugs before their health declines have a 96% lower risk of transmitting the virus to a partner, a breakthrough global study said.
The large study that covered mainly heterosexual couples in Africa, India and the Americas was hailed by Aids experts as a game-changer that will transform how the incurable disease is managed.
Until now, antiretroviral therapy was known to improve the health of HIV-infected patients, but this is the first study of its kind to show a solid impact on preventing transmission to an HIV-negative partner.
"This is excellent news," said Myron Cohen, lead investigator on the study and director of the Institute of Global Health and Infectious Diseases at the University of North Carolina at Chapel Hill.
The randomised clinical trial began in 2005 and included 1,763 couples 97% of whom were heterosexual, and was carried out at 13 sites in countries including Brazil, Thailand, Zimbabwe, India and South Africa.
The randomisation phase was halted early once researchers realised that the drug regimen was having such a significant blocking effect on the risk of spreading the infection, which afflicts 33 million people worldwide.
"The study was designed to evaluate the benefit to the sexual partner as well as the benefit to the HIV-infected person," said Cohen.
First randomised HIV clinical trial
"This is the first randomised clinical trial to definitively indicate that an HIV-infected individual can reduce sexual transmission of HIV to an uninfected partner by beginning antiretroviral therapy sooner."
Under the randomised trial, some couples were placed into a delayed group in which the infected partner began taking antiretroviral therapy (ART) only when a type of T-cell known as CD4 dipped below 250 cells per mm cubed, or if he or she developed an Aids-related illness.
The other group began taking ART immediately. In that group, just one case of HIV transmission was observed.
There were 27 HIV transmissions in the delayed group that could be traced directly to the infected partner, a difference the study described as "highly statistically significant."
National Institute of Allergy and Infectious Diseases chief Anthony Fauci hailed the findings.
"Previous data about the potential value of antiretrovirals in making HIV-infected individuals less infectious to their sexual partners came largely from observational and epidemiological studies," said Fauci.
"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."
According to Wafaa el-Sadr, a member of the executive committee of the HIV Prevention Trials Network (HPTN), the group that did this study, the findings took time to produce but should have a major impact on treatment guidelines.
"I think HPTN 052 will always be recognized as a landmark study that truly may transform treatment as well as prevention of HIV globally," she said.
Sadr, who is also a professor of medicine and epidemiology at Columbia University in New York, said the couples in the study would continue to be followed.
"Everybody who was not offered immediate treatment is now being offered immediate treatment, now that we know what we know," she said.
The study was initially set to continue until 2015 but the independent safety and monitoring board halted the randomisation phase early "because of the very clear and remarkable benefits that were shown," she said.
"They determined that these findings were so profoundly important that they had to be shared immediately," she said.
Executive Director of the Joint United Nations Programme on HIV/Aids (UNAIDS), Michel Sidibe, described the study as "a serious game changer" that "will drive the prevention revolution forward."
(Sapa, May 2011)