The PARTNER Study, a two-year study, has reported no incidence of HIV transmission by partners with a undetectable viral load.

The latest PARTNER Study results were announced at CROI 2014
The latest PARTNER Study results were announced at CROI 2014

For some time now we’ve known that having an undetectable viral load (VL) significantly reduces the chances of transmitting the virus onto partners and thus reduces the chance of infection, but in a landmark study of 1,110 couples (40% gay couples) there were no recorded transmissions of HIV between the positive and negative partners.

The PARTNER study took on 1,110 couples – 40% of which were gay. To qualify for the study the partners had to be having condomless sex “at least some of the time” with the negative partner not receiving Pre-Exposure Prophylaxis (PrEP) or Post-Exposure Prophylaxis (PEP), the positive partner had to be receiving HIV treatment and have a viral load below 200 copies/ml. A small number of couples were excluded from the study, for VL increases or having taking PrEP / PEP.

The headline news is that out of an estimated 16,400 occasions of sex in the gay men and 14,000 in the heterosexuals there have been no reported HIV transmissions within the study couples.  A number of people in the study did become HIV positive but through genetic testing the the study was able to determine that the virus had come from outside of the relationship.

Alison Rogers from The PARTNER Study told CROI 2014 conference attendees that zero infections is not the same as zero percent risk. With a 95% confidence in their figures the team peg the risk per year at 0.45% to the negative partner, and 1% for those who engage in anal sex. But when asked what the study tells us about the chance of someone with an undetectable viral load  transmitting HIV, presenter Alison Rodger said: “Our best estimate is it’s zero.”

This is clearly great news for those couples in serodiscordant relationships, or concerned about dating someone of a different HIV status. But we must remember that though the chance of transmission is close to zero percent, there is still a statistical chance.

The PARTNER Study is still recruiting male couples, and its final results will be out in 2017. For more information about the partner study please visit:


  1. R u sexing this quote up? Painting too rosy of a picture is just as harmful to poz folks as the hand wringing public health folks ignoring and downplaying important advancement.

    But when asked what the study tells us about the chance of someone with an undetectable viral load transmitting HIV, presenter Alison Rodger said: “Our best estimate is it’s zero.” My recollection of her presentation was burst guess which conveys must less conviction.

    Can u provide citation?

  2. For anyone who fears this article is “sexed up”, go listen to the actual presentation, see the slides, and hear the Q & A at the end:
    or listen to an MP3 of just the audio portion:

    For further backup, here is an interview with the Partner study lead investigator Jens Lundgren from the University of Copenhagen:

    May I suggest a small correction to this article. The heterosexual couples had an estimated total of 28,000 condomless sex acts. I had made the same error by neglecting to add the estimated acts from the male heterosexual negative partners, to the acts of the female heterosexual negative partners.

    No one is saying this is permission for serodivergent couples to boink without rubbers. But the reality is many are doing it anyway. We might feel more comfortable about it after the study is complete and published in 2017. There is defiantly not enough data yet for the Poz top Neg bottom scenario.

    With more info from following the already enrolled gay couples, plus the additional 450 more gay couples they hope to find, it will increase the confidence level, and decrease the theoretical risk. They will never be able to say there is zero risk.

    My personal take on what we know so far is that it’s a relief on my conscious for any slip-ups I had in the past, and makes a future broken condom less stressful. (Though PEP might still be warranted in Poz top Neg bottom.) I think we can also surmise that “low risk” blow jobs could now be considered No risk (barring open wounds in the Neg partners mouth).

    To me, the biggest take away from the presentation is BIG GUN ammo in the fight against Stigma. If the final report continues the same trend it will be HUGE. Laser Guided Artillery, and Smart Bombs with Military Grade GPS

    We’d never target them at the Neg partners in serodivergant relationships. You already love of for who we are. 🙂

    There is a certain irony in the fact us Poz guys, who the Neggies are most afraid of, and immediately reject, are probably going to turn out to be the ones least likely to infect them! Our status is 100% known verses all the “think they’re neg” guys. Many of them don’t test regularly, if ever.

    The one snag here is the formerly Negative guys who caught HIV from playing someone other than their primary partner. They are withholding that data until the end of the study. With 16% catching other STIs, it’s a safe bet that there are more than a few guys who now share their partner’s daily trip to the medicine cabinet. We need to be very clear that gene sequencing proved it could not have come from their Poz partner. So few unaffected people understand even the basics of HIV, that the concept of constant mutation creating something analogous to a genetic fingerprint would be totally over their head.

  3. This i-Base report includes a table with the breakdown of types of sex – ie about 44,500 exposures and over 20,000 exposures from anal sex.

    It also tries to explain that when risk is quoted as a percentage you also need to ask about the range that this could be (called the 95% confidence interval). The actual risk could not only be anywhere in this range, but there is a small chance (2.5%) that it could be a higher risk. For a gay couple, this study calculated that the risk might be close to 10% over ten years that HIV could be transmitted. The whole presentation was about this – the 0% estimated quoted just related to the lower end of this range and you need to consider the upper end too.

    As the study collects more data for gay men, as long as there are no linked transmissions, this range will become smaller because we will be more confident that the result is real and not just happening but chance.

    One of the most interesting aspect of these results is that even with 16% (I think) of gay partners having an STI, there were still no linked transmissions. Of course, other STIs can still be transmitted, just that HIV from the partner with an undetectable viral load, wasn’t one of them.

    This study has collected more real evidence from people at risk than all the other similar studies combined. It is the first study to do this for anal sex (gay or straight) and the first for gay men.


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