A study by researchers from UCSF's Center for AIDS Prevention Studies (CAPS) found the probability of HIV infection through unprotected receptive oral sex with a man to be statistically estimated as zero.
"Our study looked at exclusive receptive oral intercourse with a male partner, and we found that the probability of acquiring HIV through that specific sexual activity is very, very low. Given that the results are based on a relatively small sample, we can not rule out the possibility that the probability of infection is indeed greater than zero," said study lead author Kimberly Page Shafer, PhD, MPH, assistant professor of medicine at UCSF's CAPS.
The study is ongoing and the findings will be amended by the researchers with greater numbers.
"While our study is the first to attempt to systematically define the risk, case reports exist of infections acquired through oral contact. I want to emphasize that, while rare, acquiring HIV infection orally is possible and that many other sexually transmitted diseases (STDs) such as gonorrhea, chlamydia, and syphilis are transmitted orally," added Shafer.
The study, presented today (August 14) at the Second National Prevention Conference in Atlanta, enrolled 198 participants from anonymous testing and counseling sites in San Francisco. The participants, 98 percent male and 100 percent identified as gay or bisexual, reported no anal or vaginal sex and no injection drug use in the six months prior to entering the study. The participants reported a median of two receptive oral intercourse partners and 98 percent reported unprotected receptive oral intercourse.
Twenty percent of the participants reported receptive oral intercourse with an HIV positive partner. Of that group, 89 percent did not use a condom and 40 percent swallowed ejaculate.
The participants were screened for HIV infection and also for recent HIV infection using both the standard test for HIV and a test for HIV that is "detuned" to detect only those HIV infections that have occurred within the six months prior to taking the test.
Out of the 198 participants, only one HIV infection was reported, and that infection had not been recently acquired and could not be attributed to the period of exclusive oral receptive intercourse. No recently acquired HIV infections were reported by any of the other participants in the study. Statistically, the study yielded a zero probability of acquiring HIV orally.