It has been suggested that US gay men have higher rates of HIV infection in comparison to US straight men because of differences in sexual behaviors. However, an article published in Sexually Transmitted Infections (BMJ) says that the differences in sexual behaviors do not fully explain the differences.

Up to 20% of urban-dwelling gay men in the USA are thought to be HIV positive. In 2005 over 50% of all diagnosed HIV infections in the USA were among gay men, say the authors. However, according to two large population surveys, the majority of gay men had similar numbers of unprotected sexual partners annually as straight men and women.

In order to study the rate at which HIV infection has spread among gay men and straight men and women, American scientists employed a succession of carefully calculated equations in various scenarios.

They analyzed data from two national surveys and estimated how many sex partners gay men and straight men and women have. They also estimated what percentage of gay men have insertive or receptive anal sex, or both.

Then they placed this data against recognized estimates of how easily HIV is passed on either by vaginal or anal sex to calculate the extent of the HIV epidemic in homosexual men and heterosexual men and women.

Their figures indicated that straight men and women would need three times the number of sexual partners per year compared to gay men, in order to have an HIV infection epidemic as large as that of gay men. Straight men and women would have to have 5 unprotected sexual partners per year.

To end the HIV epidemic, gay men would have to have very much lower rates of unprotected sex than straight men and women currently have. The reason is that HIV transmission rates are much greater for anal sex, compared with vaginal sex, write the authors.

However, they add that gay men who adopt both insertive and receptive roles are also at a significantly higher risk of becoming infected and infecting others. The person in the receptive anal sex role runs a higher risk of becoming infected than the person in the insertive anal sex role. A person who adopts both roles can more easily become infected during his receptive anal sexual encounter, and then infect another person during his insertive sexual encounter (all examples in this paragraph refer to unprotected sex).

The authors conclude that even with similar numbers of unprotected sexual partners as straight men and women, gay men are much more vulnerable to the spread of the virus through the population.

“Biological and demographic causes of high HIV and sexually transmitted disease prevalence in men who have sex with men”
Steven M Goodreau, Matthew R Golden
Online First Sex Transm Infect 2007;doi: 10.1136/wti.2007.025627

Written by: Christian Nordqvist