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Howdy, PARTNER: Gay Men and HIV Transmission Editor Bob Leahy in Conversation With CATIE's James Wilton on What the PARTNER Study Tells Us About the Risk of HIV Transmission in Gay Men Where One Partner Is HIV-Positive but Who's Viral Load Is Undetectable

June 3, 2014

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Howdy, PARTNER: Gay Men and HIV Transmission

What about "blips" in viral load? Does PARTNER tell us anything about the significance of those?

The preliminary analysis only included information from couples in which the HIV-positive partner had an undetectable viral load in the blood. However, the blood viral load was tested every 6 months, so it is possible that some of the positive partners may have had temporary blood viral load increases (or "blips") in-between study visits. Unfortunately, we don't really know how frequently this may have happened.

We do know that 343 couples in the PARTNER study were excluded from the preliminary analysis. Of particular note, 55 (16%) of these were excluded because their blood viral load was detectable. Some of these individuals may have been experiencing "blips", but they were not included in the preliminary analysis. This finding also emphasizes the importance of regular viral load testing in order to ensure treatment is working and the viral load is fully suppressed. Also, 243 couples were excluded because they missed a follow-up visit, meaning they were not fully engaged in care and receiving regular viral load tests.

It strikes me, James, that sometimes people look for study results in simple terms where simplification isn't easy. Would you agree? Let's take as an example something one of the PARTNER researchers themselves said about transmission risk, I think, of anal sex without a condom where one partner is undetectable: "Our best estimate is it's zero" she said. You don't report that. Tell me why.

As with any research study, the PARTNER results are not without uncertainties or limitations and this can make it challenging to translate the findings into simple messages. Front-line service providers need to ensure their messages are nuanced enough to be accurate, yet simple enough to be meaningful. This is hugely challenging and consensus expert consensus statements can play an important role in guiding the development of these messages.


I don't think the statement "Our best estimate is it's zero" is a very nuanced response. Say, for example, participants in the PARTNER study only engaged in a total of 10 condomless sex acts and no transmissions occurred. In this scenario, the best estimate, statistically, would also be zero. However, such a statement doesn't reflect the uncertainty associated with the finding. It also describes the risk as an absolute (zero risk), which I don't think we should be doing.

Also, this statement was the opinion of only one of the authors of the study and was provided in response to a question from the audience. The conclusion in the conference publication -- which was reviewed by all the authors and passed a peer-reviewed process -- states that the risk of HIV transmission among the stable serodiscordant couples in the analysis was "extremely low, but uncertainty over risk remains, particularly over receptive anal sex. Additional follow-up is essential ..." Although this answer is not as nice and simple as "zero", it is a more accurate and nuanced response.

I understand. James in your article you said "ART therefore represents an important new HIV prevention tool, which also has the potential to reduce the guilt, blame and anxiety associated with the possibility of transmitting HIV to a partner." Agree 100%, but why "new"? Some people have been saying this since the Swiss Statement.

The Swiss Statement was released in 2008, but we didn't have definitive evidence that treatment could prevent HIV transmission until the HPTN 052 results were released in 2011. In addition, we didn't have definitive evidence that treatment could reduce the risk of HIV transmission through anal sex until this year, when the preliminary analysis of the PARTNER study was released. I think we can agree that this is relatively "new" information. Regardless, I know we both agree that this information isn't getting to the people who need it, so for many people this information is new and this is one of the reasons we are doing this interview.

In retrospect would you say that the Swiss Statement, while put down by many at the time, was highly predictive of actual transmission risk.

I think the Swiss Statement was challenged by many because, at the time, we didn't have definitive evidence that treatment could reduce HIV transmission, yet it took a very absolute stance by stating that there is "zero" risk when certain conditions are met. Actually, since the statement was released, one of the authors has come out publicly saying they regret taking this absolute stance. This is summarized in an article on AIDSMAP.

Also, I believe the statement was developed more to influence the criminal justice system, and less to inform public health messaging, similar to the consensus statement released by a group of Canadian scientists last month. That being said, I think the Swiss Statement did have some positive impacts, particularly as it helped improve awareness about the potential lowered risk when the viral load is undetectable and provided the impetus to perform additional studies such as HPTN 052 and the PARTNER study.

Ok James let's move on to implications of the PARTNER study. Do you think we should be reacting to it now or waiting until the final results are in to adjust our prevention messaging or even suggest to gay men that certain activities may be much safer than was previously established?

I think we should be reacting now to what we can confidently conclude from the PARTNER study results. For example, our messaging should say that we have definitive evidence that treatment can dramatically reduce the risk of HIV transmission through receptive anal sex and that this reduction seems to be equivalent to the reduction for vaginal sex. However, based on the PARTNER results, I think our messaging should also say that the risk when undetectable may still be higher through receptive anal sex compared to other types of sex. That being said, some experts (such as those at the British HIV Association) think that the risk is reduced to the same levels for both vaginal and anal sex, under certain conditions.

Anything else in the works then which may confirm -- or not -- what we have learned so far from PARTNER?

The PARTNER study stopped following participants in April of this year, so I expect that the full analysis will be published later this year or early next year. This will include information on the gay couples included in this preliminary analysis, but followed up until April 2014 instead of November 2013. Hopefully, no HIV transmissions will have occurred and the upper confidence limit for receptive anal sex will be closer to zero.

It is the PARTNER2 study that is just getting started and won't conclude until 2017. This study is continuing to follow the gay couples enrolled in the original PARTNER study and is attempting to enroll over 400 more. The main purpose of this study is to collect more data on receptive anal sex in order to drive that upper confidence limit down.

There is also a similar study ongoing in Australia, called the Opposites Attract study. Once this and the PARTNER studies are completed, we will have a very large amount of data on this topic, which we will hopefully be able to combine into a single analysis. The estimate from this analysis will allow us to be very confident regarding the "true" risk of HIV transmission when the viral load is undetectable.

That's something to look forward to then. One final question. It strikes me, James, that HIV prevention, and in fact the choices that gay men in particular have to make about their sexual risk taking, are having to become increasingly science based -- and the science is quite complex. It's also evolving. How does that increasing complexity affect your job and in fact the role of CATIE as a player in providing evidence to inform gay men's choices?

It is challenging, for sure. The science is complex and there are no simple answers that apply to everyone. As I mentioned earlier, when it comes to developing messages on the science, it is about finding a balance between capturing the nuances and keeping it simple and meaningful. It is also important for these messages to be provided in a way that is sex positive, non-judgmental, and non-prescriptive.

It is also important to keep in mind that the science and the numbers are only one part of helping gay men make informed decisions. There are so many other things that come into play and may need to be discussed, such as context, relationships, trust, intimacy, mental health, alcohol and drug use, stigma, access to care and treatment, and so on. In some cases, the science and numbers may only need to be a small part of the process in helping a person come to a more informed decision.

In the near future, I really hope we see some expert consensus statements and counselling guidelines on this topic coming out of Canada because the guidance is really needed. I hope CATIE, as well as front-line service providers and community members, will be involved in their development.

Agreed. James, as always thanks for talking to It's been a real pleasure.

Thanks Bob.

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