STUDY: 16,899 Condomless Sex Acts, Zero HIV Transmissions in Mixed-Status Couples

Treatment as prevention -- also known as TasP -- is once again proven to be an effective strategy.

A new study, Opposites Attract, found zero cases of HIV transmission within male couples in which one partner is HIV-negative and the other is HIV-positive and "undetectable" -- meaning antiretroviral treatment has suppressed the virus in the body, reports AIDS Map.

The study tracked 358 same-sex couples from Brazil, Thailand, and Australia over the span of four years and 16,899 reported acts of condomless anal sex. It further corroborated the findings of the previous PARTNER study, which also showed no HIV transmissions in mixed-status relationships where the virus is suppressed.

At the beginning of the study, 77.9 percent of HIV-positive partners were undetectable. That number rose to 98 percent by the study's end, after treatment was made available. In total, 0.9 percent of condomless sex acts occured when a partner had a detectable viral load.

In addition, 32.1 percent of HIV-negative partners had taken PrEP -- pre-exposure prophylaxis, a the daily dosage of a drug to prevent HIV -- by the end of the study, usually as a precaution with sexual partners outside the relationship. Three men did contract HIV during the course of the study, but genetic tests showed that the source was not the primary partner.

The findings were presented Tuesday at the Ninth International AIDS Society Conference on HIV Science in Paris by lead researcher Andrew Grulich.

"We think this is a really exciting result and adds to a body of research that HIV is not passed on in the context of undetectable viral load, even with high rates of sexually transmitted infections," said Grulich, of the University of New South Wales in Australia, according to Poz.