No increase in sexual risk-taking seen in partners who know they are protected from HIV transmission

HIV-negative partners in heterosexual serodiscordant couples who use prophylactic drugs to protect against HIV transmission do not show any significant increase in risky sexual behaviour, even when they know they are protected, according to new results published in The Lancet Infectious Diseases.

An international team of researchers, led by Dr Jared Baeten of the University of Washington, in Seattle, USA, used findings from the Partners PrEP study – which in 2011 established for the first time that pre-exposure prophylaxis could protect HIV-negative men and women in serodiscordant couples from HIV transmission – to determine whether people's knowledge that they were protected from HIV by the regimen affected the sexual behaviour of HIV-negative partners.

"Evidence for the effectiveness of new HIV prevention strategies, including pre-exposure prophylaxis, has spurred optimism that the global HIV epidemic might be reversed," says Dr Baeten. "However, an important question is whether HIV-negative partners who know they're protected by prophylaxis will compensate for this by increasing their sexual risk-taking, such as through increasing their levels of unprotected sex."

The researchers analysed data on over 3000 study participants, for up to 12 months before and 12 months after the protective effects of pre-exposure prophylaxis were demonstrated in the study. In addition to receiving prophylactic drugs, all study participants underwent risk-reduction counselling, safety monitoring, pregnancy testing, and tests for the sexually transmitted infections gonorrhoea, chlamydia, and trichomoniasis.

Once the protective effects of pre-exposure prophylaxis were established in 2011, the trial results were disseminated to study participants and their participation in the research continued thereafter.

After the results were revealed to study participants, the researchers found no significant difference in the level of unprotected sex taking place between partners.

Before the study results were revealed, the researchers had already noted a gradually decreasing trend in the frequency of unprotected sex, suggesting that the risk counselling and other measures provided as part of the study may have been effective; this trend did not change after study participants became aware that pre-exposure prophylaxis provided protection from HIV transmission.

The findings did show a small, but significant increase in the frequency of unprotected sex outside the study partnership after the findings were unmasked, although this increase was relatively small and was not accompanied by increasing rates of STI infection or pregnancy.

According to Dr Baeten, "To our knowledge, this study provides the first empirical data on sexual behaviour in heterosexual people receiving open-label oral pre-exposure prophylaxis for HIV prevention. The results provide encouraging evidence that behavioural changes as a result of pre-exposure prophylaxis might not undermine its strong HIV prevention and public health benefits."

In a linked Comment, Dr Kristen Underhill and Dr Kenneth Mayer write that, "The Partners PrEP analysis provides an important advance in the measurement of behaviour among serodiscordant couples using pre-exposure prophylaxis. Future research should examine the behaviours of pre-exposure prophylaxis users outside trial settings, behavioural strategies for optimisation of pre-exposure prophylaxis uptake and adherence while decreasing risk-taking, methods for assessment of users' behaviours over time, and methods for training providers. Researchers and implementers should also investigate the context of behaviour among pre-exposure prophylaxis users; individuals might have personally meaningful reasons to take risks, such as fertility desires, and understanding these motivations can strengthen efforts to support pre-exposure prophylaxis users before, during, and after use."