Risk of HIV Infection Attributable to Oral Sex Among Men Who Have Sex With Men and in the Population of Men Who Have Sex With Men

Since HIV was identified as being sexually transmitted, there has been considerable interest in the risk associated with performing fellatio. Although early studies found no independent risk for fellatio, the high correlation among multiple sexual practices raised the possibility that risk existed but could not be detected. Subsequently, case reports accumulated, largely among men who denied other risk behaviors. Researchers acknowledged that fellatio, although not an efficient route of infection, nonetheless appeared to carry a small risk.

Current safe sex guidelines specify that unprotected orogenital sex is unsafe but low risk. A recent study of primary infection in San Francisco reported that 8 percent of HIV-positive participants acquired HIV from fellatio. This finding has been widely interpreted that as many as 8 percent of HIV infections among MSM are attributable to fellatio. The population-attributable risk percentage (PAR%) is of special interest, because even a low-risk exposure could result in a substantial proportion of infections.

The authors present preliminary results from an ongoing study investigating orally acquired HIV infection demonstrating: that such infection is rare; and conduct analyses using previously published data to show that the PAR% of HIV attributable to fellatio is also extremely low.

From December 1999 to 2001, individuals seeking HIV testing at an anonymous testing site in San Francisco were screened to identify those who in the past 6 months reported no anal or vaginal sex, had not injected drugs, and had performed fellatio on at least one male partner. Eligible participants completed a pre-HIV test survey, measuring a 6-month history of sexual practices. Post-interview HIV serology was conducted to determine participants' HIV serology using enzyme immunoassays, Western blot confirmation, and a sensitive/less sensitive enzyme immunoassay strategy to identify recently acquired infection.

Of 10,283 anonymous testing site clients, 413 (4 percent) were eligible, and 243 (2.3 percent) participated. Of those, 239 (98 percent) were men, whose median age was 39 years, and all were MSM. Four women were dropped from the analysis.

No recently acquired HIV infections were detected and the estimated probability of orally acquired HIV was 0. The median number of fellatio partners in the past 6 months was three, almost all (98 percent) were unprotected. One-third (35 percent) reported getting semen in their mouth, and of those, 70 percent swallowed it. Fellatio on a known HIV-positive partner was reported by 28 percent; of those, 81 percent did not use a condom, and 39 percent had swallowed ejaculate.

The PAR% rises as the number of partners increases: PAR% for one fellatio partner was estimated at 0.18 percent, for two fellatio partners at 0.25 percent and for three fellatio partners as 0.31 percent. The cumulative PAR% for one to three fellatio partners could thus be 0.74 percent.

The authors' results are based on a modest sample size; therefore, they cannot rule out the possibility that the probability of infection is indeed greater than zero. The calculations showing very low PAR% are consistent with the findings of extremely low individual risk. In addition, if one considers that only a fraction of those who report fellatio are actually exposed to semen (35 percent), the PAR% will be considerably lower.

"These data confirm that the risk of HIV infection attributable to fellatio among MSM and in the MSM population is especially low," the authors concluded. "It is important that health professionals, including HIV counselors have valid information to impart to their sexually active clients. If individuals believe that the risk of HIV from fellatio is high or on a par with well-documented high-risk exposures such as anogenital sex, they may not feel that sexual behavior choices make a difference. Acquiring HIV through fellatio is significantly less risky than from anal sex, and therefore one's choice of sexual practices do matter."

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