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
“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.
The study’s co-authors are Caroline Shiboski, DDS, MPH, PhD, assistant clinical
professor in UCSF’s School of Dentistry’s stomatology department; James W.
Dilley, MD, executive director of UCSF’s AIDS Health Project; Joyce Balls,
project coordinator at UCSF CAPS; Willi McFarland, MD, PhD, San Francisco DPH
HIV Seroepidemiology Unit and UCSF Center for AIDS Prevention Studies; Deborah
Greenspan, DSc, professor of clinical and oral medicine in UCSF’s School of
Dentistry’s stomatology department; Stephen Shiboski PhD, and Dennis Osmond,
PhD, both associate adjunct professors in UCSF’s Department of Epidemiology and
The study is funded by the National Institute of Dental and Craniofacial