An analysis by Dawn Smith of the US Centers for Disease Control (CDC) reported at the 20th Conference on Retroviruses and Opportunistic Infections (CROI 2013) on 4 March has provided the first estimate of the efficacy of condoms in preventing HIV transmission during anal sex since 1989. It found condoms stop seven out of ten anal transmissions – the same efficacy found by the 1989 study.
However, it also found that sometimes using condoms is not effective at preventing HIV infection, and that long-term 100% condom use is a minority behaviour: only one-in-six gay men actually managed to maintain it over the three- to four-year time frame of the analysis.
One ongoing problem in assessing the effectiveness of different HIV prevention methods is that anal sex is under-studied. We do not have enough data on rectal viral loads and their effect on transmission, or on whether HIV treatment reduces transmission via anal sex as well as it does for vaginal sex.
We are also unclear about to what extent condoms actually prevent HIV transmission in anal sex. This last fact may seem surprising, given that condoms have been recommended since the mid-1980s as the only effective HIV prevention method for gay men who have anal sex.
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By Gus Cairns