Couples in which one partner is HIV-positive have a low risk of transmitting the disease if the infected partner is on antiretroviral drugs, a new study found, even if they are not using condoms.

Why it matters:

Scientist have been studying for decades whether HIV-positive individuals who take certain combinations of drugs, called antiretroviral therapy (ART), will infect their partners with the virus. A landmark study, which mostly enrolled heterosexual couples, found that ART taken by infected individuals reduced the risk of HIV transmission by 96 percent.

But many of the people in that study also wore condoms, which can help prevent HIV. So it remained unclear how effective the drugs are on their own, and whether the results also applied in homosexual couples.

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The nitty gritty:

Over an average of 1.3 years, researchers followed 888 couples in which the infected partner was taking ART. About one third of the couples were men who had sex with men — a group for which less data on the effectiveness of ART had been available. The researchers found no transmission of HIV to the uninfected partner during the study.

The study was purely observational, following couples who were already receiving ART and who did not plan on using condoms. Participants were recommended, at each of their visits, to use condoms during sex, and were given information about other drugs they could take to minimize their chances of acquiring HIV. The findings were published Tuesday in the Journal of the American Medical Association.

But keep in mind:

The small sample size for some categories — for example, only 60 heterosexual men engaged in anal sex — means that some types of sex had less robust evidence than others.

The research is ongoing, said Dr. Alison Rodger, first author on the new study and a professor of infectious diseases at University College London. The team is trying to recruit more gay men so that they can improve the precision of their estimates of HIV transmission risk.

The bottom line:

This study adds further weight to the evidence that suppressive ART is very effective at preventing HIV transmission if it’s used diligently.

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