Number of Partners Doesn't Explain Gay HIV Rate

"That puts gay men at much higher risk overall," he said.

In addition, HIV transmission is more easily transmitted through the penis than via the vagina or the anus, Goodreau said. Heterosexuals tend to maintain the same role (insertive vs. receptive), while gay men can switch roles -- making the transmission of HIV more likely, he noted.

So, for gay men and straight men who have the same number of partners and have unprotected sex, gay men are more likely to transmit and receive HIV, Goodreau said. "That's why you can get huge epidemics among gay men and virtually none among heterosexual men," he said.

To end the HIV epidemic, gay men would need to have significantly lower rates of unprotected sex than those seen among the straight men, Goodreau believes.

One expert believes the study does have its flaws, however.

"The information here is mostly based on people's reports of their own behavior," said Philip Alcabes, an associate professor at the School of Health Sciences of Hunter College/City University of New York. "When trying to make use of information on self-reported sexual behavior, we have to remember that it isn't clear that anybody tells the truth," he said.

More information

For more on HIV, visit the U.S. Department of Health and Human Services.

SOURCES: Steven Goodreau, assistant professor, anthropology, University of Washington, Seattle; Philip Alcabes, Ph.D., associate professor, School of Health Sciences, Hunter College/City University of New York; Sept. 12, 2007, online edition,Sexually Transmitted Infections