Partner Study
The ongoing PARTNER study has recently published research which adds important data to our knowledge about preventing HIV transmission. This study included 1166 serodifferent couples (548 were heterosexual) where the positive partner was on effective antiretroviral treatment (ART) with suppressed viral load and who also reported sex without a condom. During the follow up period of 1.3 years, there were no documented cases of within-couple HIV transmission.
You can read the research report in JAMA or you can read a shorter bulletin about the study on the i-base website.