HealthDay News — Pre-exposure prophylaxis in the days before and after a sexual encounter with an HIV-positive partner can be effective prevention, according to two studies presented at the annual Conference on Retroviruses and Opportunistic Infections, held from Feb. 23 to 26 in Seattle.

Previous studies have demonstrated the efficacy of tenofovir/emtricitabine (TDF/FTC), when taken regularly as pre-exposure prophylaxis (PrEP), in reducing the risk of HIV infection.

“There are concerns that this benefit might be counteracted by users of PrEP engaging in riskier sexual practices, increasing their chance of exposure to HIV and other sexually transmitted infections (STIs),” noted Sheena McCormack, Infections Group, MRC Clinical Trials Unit at University College London, London, United Kingdom and colleagues.

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To investigate the efficacy of PrEP and HIV exposure, McCormack and colleagues analyzed 545 men who have sex with men (MSM) from 13 sexual health clinics in England from November 2012 to April 2014. The patients all tested negative for HIV 4 weeks prior to enrollment and reported condomless anal intercourse within 90 days.

The participants were randomized to receive open-label daily TDF/FTC either immediately or after a deferral period of 12 months. They were followed quarterly.

Of the 545 patients, 3 HIV infections were observed in the group who immediately received TDF/FTC treatment; 19 infections were observed among those who were assigned deferred treatment, despite 174 prescriptions of post-exposure prophylaxis (PEP).

“In this high incidence cohort, daily TDF/FTC conferred impressive protection against HIV, and higher than the levels previously observed in the placebo-controlled trials,” concluded the researchers. “Concerns that effectiveness would be undermined in a real-world setting were unfounded.”