GROUNDBREAKING results from an Australian-first study of HIV transmission in serodiscordant couples indicate a very low risk of transmission when the HIV-positive partner is receiving effective treatment.

The Kirby Institute’s Opposites Attract study reported zero HIV transmissions between men in serodiscordant couples — where one is HIV-positive and one is HIV-negative — where the HIV-positive partner is on treatment with an undetectable viral load

These interim results halfway through the four-year study mirror international studies like the Partner study, which last year also reported zero HIV transmissions between partners in serodiscordant couples.

The study’s chief investigator Andrew Grulich told the Star Observer these results cover a range of sexual behaviour, including behaviour typically seen as carrying a high risk of HIV transmission.

For example, he said the interim findings looked at almost 6000 recorded acts of condomless anal sex, as well as instances of “strategic positioning”, which involves a HIV-negative person in a serodiscordant couple being the insertive partner.

“There’s quite a lot of condomless anal sex happening, so it’s pretty impressive that despite that large number of acts of condomless anal intercourse there have been no linked transmissions,” he said.

“There were about 3500 acts where the negative partner was insertive, so that’s lower risk for the negative partner, but there were over 2000 acts where the negative partner was in the receptive position. So it’s not that these men are entirely minimising their risk. They are slightly, in that the negative partner does report more insertive than receptive sex.”

Grulich cautioned that the study needed more participants in order to be sure of the true impact of effective treatment on HIV transmission during condomless sex, explaining at present the statistical risk could be as high at 4.2 per cent, even with zero transmissions recorded.

“Statistically, if you’ve got a small sample, you can be less certain in your confidence that it truly is a zero transmission risk,” he explained.

“Statistically speaking, our results are compatible with up to a four per cent risk per year, even though we saw no transmissions. If we can increase the size of the study over the next couple of years we can be much more certain, provided we continue to see no transmissions, that the true risk is truly zero.”

These interim results support the “treatment as prevention” paradigm already operating within much of Australia’s HIV sector, where early and effective HIV treatment is used as a strategy to reduce transmission rates.

The results have been welcomed by HIV organisations as evidence for the effectiveness of treatment as prevention strategies.

“While we have had international studies increasingly demonstrating that treatment as prevention works, we now have an Australian study clearly indicating population health benefits for gay men,” ACON chief executive Nicolas Parkhill said.

“We know that treating HIV early now has a significant prevention impact and it is essential that service systems, policy environments and crucially, gay men, mobilise around the opportunities that this evidence provides.”

Living Positive Victoria executive director Brent Allan echoed Parkhill’s comments about effective treatment, and hoped the results would go some way to reducing HIV stigma.

“Stigma and fear of knowing and disclosing our HIV status remains an underlying factor driving the HIV epidemic,” he said.

“These findings also have a dramatic effect upon our confidence to disclosure our HIV status to sexual partners knowing that the likelihood of infecting someone is so markedly diminished when we are on treatments and maintaining an undetectable viral load.”

For more information about the Opposites Attract study, including how to get involved, visit the website.

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