HIV/AIDS: S.F. Study Estimates Oral, Anal Sex Infection Risks
In the first mathematical risk assessment of HIV infection, the San Francisco Department of Health's study of 1,583 men "suggests that AIDS remains a difficult disease to contract but that steps taken by some men to lower their risk are not as effective as some have hoped," the San Francisco Chronicle reports. When an uninfected partner engages in unprotected receptive anal course with an HIV-positive partner, "chances are one in 120 that he will become infected." However, oral sex, widely considered "safe," poses a one-in-2,500 chance that HIV-infected semen will transmit the disease. Even condom use poses risks, as only half of the 49 men in the study group who contracted HIV reported "having unprotected sex with a partner who was either HIV positive or not known to be uninfected." Even more "provocative" was the study's finding that men who engaged in receptive anal intercourse with an HIV-positive partner and used condoms "were only one-third less likely to contract the virus than those who used no condoms at all." Susan Buchbinder, the report's senior author, said, "The data tell us that, when you have receptive anal intercourse, you are at greater risk, regardless of whether you reported using a condom," but added that the data require "confirmation." She said of the risks associated with oral sex, "We're not talking thousands of times less risky. We're talking about 10 times less risky." Dan Wohlfeiler, a researcher at the University of California-Berkeley School of Public Health, said, "We've always said that oral sex is lower risk but not risk-free. The odds may be one in 2,000 but if you have 10,000 going on at any one time, someone is going to draw that unlucky card."
What to Do
Buchbinder noted that since the study found that becoming HIV positive from a single act of unsafe sex with a "partner who was not known to be HIV negative" carries a one in 370 probability --equivalent to the risk of becoming infected via an accidental needle stick -- doctors should prescribe a short course of antiviral therapy to men who fear they may have been infected, as is the practice with health practitioners who are stuck by needles. The study also reported that unprotected insertive anal intercourse with an HIV-positive partner carries a one in 1,666 chance of infection, while uninfected women who have unprotected vaginal intercourse with an HIV-positive partner have a one in 1,000 or one in 2,000 chance of infection. However, Buchbinder emphasized that "individual infection rates varied widely," with some individuals contracting HIV through a single high-risk encounter while others remained HIV-negative after "hundreds of high-risk sex acts" (Russell, San Francisco Chronicle, 8/13).