Back HIV Prevention Treatment as Prevention EACS 2017: High HIV Incidence from Non-Primary Partners and Low PEP and PrEP Use Seen in PARTNER Study

EACS 2017: High HIV Incidence from Non-Primary Partners and Low PEP and PrEP Use Seen in PARTNER Study


HIV incidence among the HIV-negative gay men in the PARTNER 1 and 2 studies, due to sex with partners outside their main relationship, was high, and very high among partners who admitted having condomless anal sex with non-primary partners, researchers reported at the recent 16th European AIDS Conference (EACS 2017) in Milan.

[Produced in collaboration with]

Conference attendees heard that even now, based on the latest data from the PARTNER 2 study, only 5% of HIV-negative participants are using pre-exposure prophylaxis (PrEP), even though over a third have had condomless anal sex with non-primary partners.

The data were presented by Valentina Cambiano of University College London, who is one of the investigators in the PARTNER studies.

PARTNERis arguably one of the most significant HIV prevention studies ever conducted. It studies couples where one partner has HIV and the other does not, and its primary aim is to try to quantify the risk of transmission from a person on antiretroviral treatment who has a fully suppressed viral load. While enrollment of heterosexual couples stopped at the end of PARTNER 1 in 2014, it was decided that more data on gay men were needed, so PARTNER 2, for gay couples only, is still underway.

PARTNER made headlines when in 2014and again in 2016, the researchers confirmed that there had been no transmissions from an HIV-positive partner who was on antiretroviral therapy and virally suppressed in, by 2016, an estimated 58,213 condomless sex acts. These data allowed the researchers to establish the maximum possible likelihood of transmission, and to announce that, most likely, the chance of an HIV-positive partner with a fully suppressed viral load below 200 copies/mL passing on HIV was zero, or statistically indistinguishable from it.

PARTNER, and other studies like Opposites Attract and HPTN 052, have provided the evidence base for the success of "treatment as prevention" and for the U=U (Undetectable Equals Untransmittable) campaign.

However, there were HIV infections in PARTNER: 11 of them by 2016, with 10 of these gay men. In all cases, however, phylogenetic testing showed that the infecting virus came from someone other than the person's primary partner. Eight of the 11 infected people told researchers they had had condomless sex with partners other than their primary partner; the other 3 must have done too.

Cambiano told the conference that multiplying the number of infections by the amount of time people were in follow-up before infection leads to an estimated HIV incidence of 2.3% a year -- quite high. However, if only the 8 men who admitted to having condomless anal sex with other partners are counted, then incidence becomes very high -- 7.2% a year, or higher than that seen in the placebo arm of the Ipergay PrEP trial.

In short, just because your main partner is undetectable, it does not mean you are safe from HIV if you have condomless sex elsewhere. In these cases, it would make sense to use post-exposure prophylaxis (PEP) or PrEP -- but how many in PARTNER were doing so?

Cambiano and colleagues studied PEP and PrEP use in the 737 HIV-negative partners who had answered both the baseline sexual behavior questionnaire and a questionnaire on at least 1 follow-up visit.

They had been in the study for an average of 1.6 years and had averaged 1 year of condomless anal sex with their primary HIV-positive partner. 35% said they had had condomless anal sex with other partners and 22% had been diagnosed with a sexually transmitted infection other than HIV. The researchers estimated that on average the men had 35 acts of condomless anal sex per year with other partners. They also worked out that the total number of condomless anal sex acts with main partners now amounted to 69,098 acts, strengthening the conclusion that HIV transmission is not taking place when the main partner has undetectable viral load.

At baseline, in both phases of the study, over 1 in 6 men (17.5% in PARTNER 1 and 17.9% in PARTNER 2) had ever taken PEP. But far fewer had ever taken PrEP; only 1.5% in PARTNER 1 and 3.9% in PARTNER 2. This is not that surprising, as PARTNER is a mainly European study, and PARTNER 1 recruited in 2010 and PARTNER 2 in 2014.

During the studies a further 3% of participants in PARTNER 1 and 4.6% in Partner 2 used PEP, and 3% and 5%, respectively, used PrEP. This means that in PARTNER 2, 8.2% of the HIV-negative partners used PEP and/or PrEP.

However, if the partners admitted to having had condomless anal sex with other men in the follow-up questionnaire, then they were twice as likely to have used PEP and 3 times as likely to take PrEP: 8.7% of these men took PEP and 10.3% were using PrEP, meaning that nearly 16% had used PEP and/or PrEP.

The 10.3% using PrEP numbered 253 men. A majority (58%) were in the U.K., with smaller numbers in other countries: 11% each in France and Switzerland, 8% each in Germany and the Netherlands, and 4% in Spain.

This finding meant that among men reporting condomless anal sex with outside men, PEP or PrEP only covered 12% of sex acts that risked HIV infection and only 1.5% of acts among men who did not report it. It can easily be seen that if the negative partners had covered, say, 80% of their possibly risky sex acts with PEP or PrEP instead of 16%, then HIV incidence would have been considerably lower.

Cambiano commented that the low level of PEP and PrEP use and the high HIV incidence seen from sex outside the main relationship were of concern.

"PrEP eligibility discussions with HIV-negative [men who have sex with men] should ensure that risks from all sexual contacts are taken into consideration, and routes to securing PrEP discussed," she said.



V Cambiano et al. Use of PEP and PrEP among HIV Negative MSM in the PARTNER Study. 16th European AIDS Conference. Milan, October 25-27, 2017. Abstract PS11/4.