A Kiss Is Just a Kiss

If you tell a patient that the risk of transmitting HIV infection during unprotected vaginal intercourse is 1 in 500 -- which it is -- some patients will deem that risk acceptable. (If they didn't, we wouldn't be seeing so many new cases of HIV disease in women whose only risk factor is heterosexual intercourse with an infected partner.) If, on the other hand, you tell a patient that there is a 1 in 2,000,000 chance that HIV may be transmitted during mouth-to-mouth contact, many patients will wonder if they are putting people who are HIV-negative at risk by kissing them.

Why? It seems clear that the concept of "odds" doesn't adequately convey a sense of the degree of risk involved in such acts. That should come as no surprise to us. We are, after all, a nation of gamblers. We risk billions of dollars each year on state lottery tickets alone, and we all know how long those odds are. Maybe what we need is another way of explaining risk to our patients -- a way that effectively conveys the degree of risk, but does so without leading our patients to assume they can continue to beat very short odds, or causing them to worry unduly about very long odds.

The inadequacy of "odds" as a way of explaining relative risk was brought home to all of us several months ago, when a C.D.C. report on a case of apparent oral-oral HIV transmission got picked up by the mass media -- and generated a kind of mass hysteria. What many laymen took that report to mean was that HIV could be transmitted simply by kissing someone, and it didn't help to tell them that the odds are better that they will be hit by lightning than that they will get infected -- or infect someone -- in this way.

The case of apparent oral-oral transmission that Dr. Nancy Padian reported to the C.D.C. was in all respects a highly unusual one. As Dr. Padian has taken great pains to explain, this singular event occurred after both partners, the HIV-positive male and the HIV-negative female, had undergone dental surgery. He was highly viremic at the time; she had mouth lesions sufficiently large to make her susceptible to infection by this route; and there was extensive mouth-to-mouth contact. The odds that this same set of circumstances would ever arise again are, well, astronomical. You've got a better chance of winning the lottery, and we all know how long those odds are.

For patients, the lesson to be taken from this isolated and unusual case is that poor oral hygiene is a potential mode of infection -- and HIV-positive individuals with bleeding mouth sores shouldn't kiss anyone on the mouth. For healthcare providers, the lesson is that we should avoid talking about odds, and we should reassure our patients that they don't need to be worried about isolated and unusual cases like the one Dr. Padian reported to the C.D.C. The vast preponderance of all new HIV infections are transmitted through unprotected vaginal or anal intercourse, and this is where we need to focus our prevention efforts. What we need to be telling our HIV-positive patients is: Kiss anyone you want, anywhere you want. But never, ever have unprotected intercourse.

Paul A. Volberding, M.D., is Editor-in-Chief of HIV Newsline and AIDS Program Director at San Francisco General Hospital.