13 September 2007
Scientists Mull Gay-Straight HIV Conundrum
by George Atkinson

Over half of new HIV infections diagnosed in the US are among gay men, but two large population surveys have shown that most gay men had similar numbers of unprotected sexual partners per year as straight men and women. Now, sexual health researchers have crunched the numbers on HIV infection rates in an effort to work out why there is such a disparity between gay and straight transmission of the virus.

The new study, published in the journal Sexually Transmitted Infections, applied a series of equations in different scenarios to study the rate at which HIV infection has spread among gay men and straight men and women. The researchers used figures taken from two national surveys to estimate how many sex partners gay men and straight men and women have, and what proportion of gay men have insertive or receptive anal sex, or both.

The figures were then analyzed in the context of accepted estimates of how easily HIV is transmitted by vaginal and anal sex to calculate the size of the HIV epidemic in gay men and straight men and women. The results showed that for the straight US population to experience an epidemic of HIV infection as great as that of gay men, they would need to average almost five unprotected sexual partners every year - a rate almost three times that of gay men.

The researchers note that this is because transmission rates are higher for anal sex than they are for vaginal sex. But they add that "role versatility," whereby people adopt both "insertive" and "receptive roles," also plays an important role. This means a gay man can be easily infected through unprotected receptive sex, and then infect someone else through insertive sex.

The study concludes that gay men are therefore far more susceptible to the spread of the virus through the population, even with the same numbers of unprotected sexual partners. To end the HIV epidemic, say the researchers, gay men would need to have rates of unprotected sex several times lower than those currently evident among the straight population.

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Big Rise In Unprotected Gay Sex Has Experts Worried

Source: Sexually Transmitted Infections