There is only one scientific study that actually calculated the odds of getting HIV while topping. There have been occasional men who insist that they got HIV from topping only, however, this seems to be rare. In very rough numbers, you are about ten times less likely to get HIV from topping than from bottoming.
In my experience, the most common problems are the standard STI's including minor infections. The chances of catching something in a bathhouse are probably 100 times greater than from fuck buddies. Washing and pissing afterward is a good idea even if there isn't any scientific proof that this helps.
The scientific studies have not been able to calculate exact odds because they have been unable to get a large enough number of men (due to budget reasons). When President Bush took office in 2000, his administration virtually cut off all of the funds for HIV studies on gay men and so there has been very little new since this article was published: (The full article is only available for a fee or from a medical library. The following abstract is free.)
= = = = FROM COPYRIGHT FREE U.S. Government Source = = =
American Journal of Epidemiology - Volume 150 Number 3 - August 1, 1999
"Per-Contact Risk of Human Immunodeficiency Virus Transmission between Male Sexual Partners." Eric Vittinghoff, John Douglas, Frank Judson, David McKirnan, Kate MacQueen, and Susan P. Buchbinder (Department of Epidemiology and Biostatistics, University of California San Francisco, 74 New Montgomery, Suite 600, San Francisco, CA 94105)
Am J Epidemiol 1999;150:306-11
The risk of human immunodeficiency virus (HIV) transmission from various types of homosexual contact, including oral sex, is of biologic, epidemiologic, and public health importance. The per-contact risk of acquiring HIV infection from specific acts was estimated in a prospective cohort study of 2,189 high-risk homosexual and bisexual men, conducted in San Francisco, California; Denver, Colorado; and Chicago, Illinois, in 1992--1994. During 2,633 person-years of follow-up, 60 seroconversions were observed. The estimated per-contact risk of acquiring HIV from unprotected receptive anal sex (URA) was 0.82 percent (95% confidence interval: 0.24, 2.76 percent) when the partner was known to be HIV+ and 0.27 percent (95% confidence interval: 0.06, 0.49 percent) when partners of unknown serostatus were included. There was heterogeneity in per-contact risk, with nine seroconversions occurring after only one or two episodes of URA. The per-contact risk associated with unprotected insertive anal and receptive oral sex with HIV-positive or unknown serostatus partners was 0.06 and 0.04 percent, respectively. URA accounted for only 15 percent of all reported sexual activity by seroconverters. As lower-risk practices become more common, they may play a larger role in propagating the epidemic and should also be addressed by interventions targeting high-risk homosexual and bisexual men.
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