partnerstudyThe PARTNER study is a large international study. It looked at the risk of HIV transmission when viral load is undetectable on HIV treatment (ART). The study enrolled 1166 couples where one partner was HIV positive and on ART, and the other was HIV negative. In order to join the study, couples had to already be having sex without condoms. The study enrolled both gay and straight couples and the average age was about 40 years old.

The main results were that there were no linked HIV transmissions from the HIV positive to the negative partner. This was after about 58,000 times when couples had sex without using condoms.

To be included in the results, viral load had to be undetectable at the most recent test. Undetectable in this study was defined as being less than 200 copies/mL. The results were not affected by other STIs. They were not affected by likely viral load blips between viral load tests.

The lack of HIV transmissions should challenge the wrongly held common assumption that there is always a risk just because someone is HIV positive.

The results actually go further. The lack of transmission challenges scientists to prove that transmission is actually possible when viral load is undetectable.

The PARTNER study – as with other studies – suggests that there is likely to be a level of viral load where HIV transmission does not occur. PARTNER suggests this might be at 50 copies/mL, or at 200 copies/mL or perhaps even higher.

The research is discussed here, with a helpful Q&A section here.

The full academic study is available free on the JAMA website.