A study published online last month in the journal The Lancet announced that HIV-positive individuals who used antiretroviral therapy (ART) reduced the risk of transmitting HIV to their uninfected partners by 92 percent.

“These observational data strongly support the hypothesis that ART substantially reduces HIV-1 infectiousness and transmission risk,” wrote the authors.

Over 3,400 couples from seven different African countries were included in the study. In each case one partner was HIV-positive and the other HIV negative, known as serodiscordance.

Although previous studies have shown that ART can reduce the risk of transmitting HIV, “there are no other studies that are published that are from discordant couples that were enrolled and then followed over time,” said Dr. Deborah Donnell, lead author of the study, in email correspondence with The AIDS Beacon.

“There are some [studies] that have been reported at conferences, but are not yet in peer reviewed journals,” added Dr. Donnell.

At the start of the study, none of the participants were receiving ART. The couples were then followed for a period of two years, and during that time, 349 HIV-positive participants began antiretrovirals.

Of the 103 total transmissions documented in the study, only one transmission occurred after the HIV-positive partner began ART, representing a 92 percent decrease in transmission risk.

Even in that one case, the participant had only been taking anti-HIV medications for four months and may not have achieved full viral suppression.

The authors called the reduction in transmission rate “highly encouraging,” although they emphasized that couples still need to understand that “potential for HIV-1 transmission to partners remains after ART initiation.”

The study also allowed the researchers to see which factors most influenced the rate of HIV transmission.

HIV-infected individuals who were not taking ART had the highest risk of transmitting the virus to their partners if their CD4 cell counts were below 200 cells per microliter of blood.

Additionally, of those participants that had CD4 cell counts higher than 200 cells per microliter of blood, 70 percent of transmissions occurred in people with blood HIV concentrations above 50,000 copies per milliliter.

The study authors suggest that once countries are able to allocate resources to fully provide ART to those with the lowest CD4 counts, focus could then be placed on providing ART to those with high blood HIV concentrations as a prevention strategy and as a movement towards providing all HIV patients with ART.

For more information, please see the article at The Lancet (abstract) and the press release at the University of Washington (pdf) website.