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
CENTER FOR DISEASE CONTROL
December 2, 2002
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."