Analysis of men who acquired HIV in the deferred arm of the
PROUD study highlights two risk factors that are far more important than any
others. “A recent history of syphilis or rectal chlamydia/gonorrhoea, or
multiple ncRAI [receptive anal intercourse without a condom] partners indicates a high
imminent risk of HIV infection,” Ellen White of University College London and
colleagues write in Sexually Transmitted
. “MSM [men who have sex with men] with any of these characteristics should be offered PrEP [pre-exposure prophylaxis]
as a matter of urgency.”

The analysis is based on the 268 participants who took part
in PROUD, the study of PrEP in England, and were randomly
allocated to the deferred arm (those who did not initially receive PrEP).

Participants’ median age was 35; 40% were born outside the
UK and 70% were recruited at a London clinic. In the previous year, 40% had
been diagnosed with rectal chlamydia, rectal gonorrhoea or syphilis. There was
a wide range of numbers of sexual partners between participants, with half
having more than ten partners in the previous three months. This was a cohort
at unusually high risk of HIV, who are not representative of the wider
population of gay men in England, but do reflect a group who were motivated to
take PrEP.

Among those in the deferred arm, 21 individuals acquired HIV
during 239 person-years of follow-up. This equates to a very high HIV incidence
of 8.8%, but incidence varied according to the risk factors reported on entry
to the study.

  • Incidence was 17.2% in individuals who had been diagnosed
    with rectal chlamydia, rectal gonorrhoea or syphilis in the previous year.
  • Incidence was 13.6% in individuals who reported having receptive
    anal sex, without a condom, with at least two partners in the previous three
  • Incidence was 1.1% in individuals with neither of these two risk

Other ways of counting partner numbers (numbers of anal sex
partners and numbers of receptive anal sex partners) were also associated with
HIV infections, but the strongest predictor was the one mentioned above. On the
other hand, there were no HIV infections in those men who reported that the only
condomless sex they had was as the insertive partner (top).

There were more HIV infections in men who reported chemsex,
had taken more HIV tests in the past year, had taken post-exposure prophylaxis (PEP) in the past year, and
who were in full-time employment, but these did not equate to statistically
significant increases in incidence.

“The results should inform eligibility criteria for MSM in
the UK and similar populations elsewhere in Europe,” the authors say. All international
guidelines include anal intercourse without a condom as a criterion, but generally without specifying the number of partners. Other criteria in guidelines include
a recent diagnosis with a bacterial sexually transmitted infection (STI), the
use of PEP and sexualised drug use.

In this study, STIs in the throat or penis were not
associated with an increased HIV risk, suggesting that PrEP eligibility
criteria should focus on rectal STIs and syphilis.