GENEVA, Switzerland--A University of California San Francisco investigator has found a number of activities that significantly increase the risk of acquiring HIV among HIV-uninfected gay/bisexual men.
In addition to having many partners, having unprotected receptive anal sex with an HIV-infected man or partners of unknown serostatus, some types of drug use, oral sex to ejaculation with a positive partner, and even being uncircumcised were associated with a 1.8-3.7 fold increased risk of infection.
Some of the risk factors were a surprise, said Susan Buchbinder, MD, director of the HIV Research Section in the San Francisco Department of Public Health and assistant clinical professor of medicine and epidemiology at UCSF. She presented the study findings here today (June 30) at the 12th World AIDS Conference.
"Unprotected receptive anal sex is clearly the riskiest behavior for contracting HIV," said Buchbinder, "but people have to recognize infections occurring from partners of unknown HIV serostatus are accounting for as many infections as those from partners known to be HIV positive."
Buchbinder said other factors associated with increased risk of HIV infection that surprised her were the association of amyl nitrate ("popper") use, oral sex with a positive partner, and being uncircumcised.
For her study, Buchbinder took the survey results of 3,257 gay men enrolled in the HIVNET Vaccine Preparedness Study in six U.S. cities, including San Francisco. The participants were interviewed, counseled, and tested for HIV every 6 months for 18 months.
Buchbinder calculated both the riskiness of particular behaviors, and the "attributable fraction" of those activities, that is, the proportion of total infections that were associated with that behavior. Although the attributable fraction doesn't tell whether the behavior causes the infection, Buchbinder said, it is a way of combining how risky the activity is with how many seroconverters actually engaged in that activity.
The fraction yields a useful number for understanding how much that behavior may be contributing to infection in the community being studied. Because men often had more than one risk factor, the attributable fraction will total more than 100 percent.
The study results found that men under the age of 35 were more likely to become infected with HIV than those 35 and older, and 76 percent of the seroconverters were under 35.
Once she equalized the differences among the men based on city, age and race, her findings also showed:
- During the course of the study, 71 men became HIV-positive, or seroconverted.
- Men who had between five and 10 male partners in six months increased their risk for developing HIV by two-and-a-half times. Men with more than 10 partners increased their risk by almost three-and-a- half times. Having multiple partners accounted for more than half of the infections.
- Men who had unprotected receptive anal sex had three-and-a-half times higher risk of becoming HIV infected, while men who reported the same activity with partners of unknown serostatus had two-and-a-half times higher risk. However, because the latter activity was much more commonly reported, each contributed to approximately 15 percent of the seroconversions.
- Uncircumcised men had more than twice the risk of being infected than circumcised men. The reasons for this are unclear, but it may have to do with the harboring of other sexually transmitted diseases, or HIV itself, under the foreskin, said Buchbinder, suggesting that in some circumstances, insertive anal sex may carry additional risk.
- The use of poppers nearly doubled the risk of infection. Because popper use was so common among seroconverting men, popper use was associated with 22 percent of the seroconversions. Buchbinder said she wasn't sure how poppers contribute to HIV infection, but speculated that they may contribute biologically (because of increased blood flow to mucous membranes) or behaviorally (by encouraging men to have more prolonged or more traumatic sexual contact, or other risky sexual practices).
- Unprotected receptive oral sex to ejaculation was associated with a three-fold increase in risk, but accounted for fewer than 5 percent of infections.
Buchbinder's findings emphasize areas critical for counseling intervention. "The fact that younger age is associated with a higher risk of HIV infection should underscore the need for prevention efforts targeted at young people," Buchbinder said. "In addition to reducing unprotected sex, counseling should focus on reducing the total number of partners. Also, gay men should be warned that poppers, injection drug use, and having unprotected receptive oral sex to ejaculation can be dangerous."
Co-investigators on Buchbinder's study are: Patrick Heagerty, Fred Hutchinson Cancer Research Center, Seattle, Wash.; Beryl Kobline, The New York Blood Center, New York; Ken Mayer, Fenway Community Health Center, Boston, Mass.; John Douglas, Denver Department of Public Health; Connie Celum, University of Washington, Seattle; and George Seage, Boston University School of Public Health.