UCSF News Office
Corinna Kaarlela, News Director
29 July 2003
No cases of HIV transmission through unprotected receptive oral sex were found by researchers at UCSF's Center for AIDS Prevention Studies (CAPS) in a new study. The study looked at men who have sex with men and who exclusively practice oral sex as the receptive partner.
"HIV infection through receptive oral sex is a very rare event-statistically our study showed a probability of zero-and is rarer than HIV infection through receptive anal intercourse using a condom," said the study's lead author Kimberly Page Shafer, PhD, MPH, assistant professor of medicine at UCSF's CAPS. The findings are being published in the November 22, 2002 issue of AIDS.
The study enrolled 239 men who have sex with men starting in 1999 from anonymous testing and counseling sites in San Francisco. The participants 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 three partners with whom they had been the receptive partner for oral intercourse and ninety-eight percent reported unprotected receptive oral intercourse. Twenty-eight percent knew their partner was HIV-infected and of those, thirty-nine percent swallowed ejaculate.
"If you compare our group, which practiced oral sex exclusively, with men who engaged in receptive anal intercourse from the same testing sites during a similar time period-and considering both those who reported using protection and those who did not-you find significant HIV transmission even among those who used protection during receptive anal intercourse," said Shafer.
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.
"Although this study is the first to try to systematically define the risk, case reports exist of HIV infections acquired through oral contact. While rare, acquiring HIV infection orally is possible and many other sexually transmitted diseases such as gonorrhea, chlamydia, and syphilis are transmitted orally," said Shafer.
The study is ongoing and the researchers will amend the findings with greater numbers. The study's co-authors are Caroline Shiboski, DDS, MPH, PhD, assistant clinical professor in UCSF's School of Dentistry's stomatology department; Dennis H. Osmond, PhD, UCSF associate professor in the department of epidemiology and biostatistics; James W. Dilley, MD, executive director of UCSF's AIDS Health Project; Willi McFarland, MD, PhD, co-director of the San Francisco Department of Public Health's HIV/AIDS Statistics and Epidemiology Unit and UCSF assistant adjunct professor of epidemiology and biostatistics; Stephen Shiboski PhD, associate adjunct professor in UCSF's Department of Epidemiology and Biostatistics; Jeffrey D. Klausner, MD, MPH, director of STD prevention and control at the San Francisco Department of Public Health and UCSF assistant clinical professor of medicine; Joyce Balls, project coordinator at UCSF CAPS; Deborah Greenspan, DSc, professor of clinical and oral medicine in UCSF's School of Dentistry's stomatology department; and John S. Greenspan BSC, BDS, PhD, FRC Path, ScD [hc], FDSRCS [Eng], professor and dean for research in UCSF's School of Dentistry.
The study is funded by the National Institute of Dental and Craniofacial Research.