Men who have sex with men (MSM) in a recent study of Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis in the United Kingdom were most likely to benefit from PrEP if they had two key risk factors, aidsmap reports. Researchers from the PROUD study, which randomized 544 U.K. MSM to receive PrEP immediately or on a deferred basis, presented findings from a new analysis of the study at the conference of the British HIV Association in Manchester, England.

The PROUD study found that HIV reduced the risk of HIV by 86 percent among the group that received PrEP, compared with the group that got Truvada on a deferred basis.

This new analysis looked at 253 of the 269 men in the deferred group, who together contributed 220 person-years of follow-up (person-years are the cumulative years participants spend in a study). Twenty of the men contracted HIV, at a rate of 9.1 percent per year.

The researchers found that two factors at the study’s outset were significantly related to a risk of contracting the virus: reporting condomless receptive anal sex with two or more men and being diagnosed with a rectal sexually transmitted infection at the beginning of the study.

Men who reported using post-exposure prophylaxis (PEP) and who said they engaged in chemsex, or sex while on crystal meth, were also more likely to contract HIV. But this link was not statistically significant, meaning it could have occurred by chance. Just the same, the researchers stressed that both these factors are indications for PrEP use according to the World Health Organization.

To read the aidsmap article, click here.