For all the blood spilled in boxing and the sweat sweated in basketball, the likeliest place for an athlete to get AIDS is off the field, in an out-of-town hotel room. Magic Johnson assumes he was exposed to HIV during unprotected sex with one of his hundreds of female admirers. Two other retired (and unnamed) NBA players with AIDS were likely infected the same way. Compared with unsafe sex and shared needles, being splattered by a linebacker's bloody nose poses infinitesimal risk. There are no known cases of HIV infection through sports, says Dr. Anthony Fauci of the National Institute of Allergy and Infectious Diseases: "You need direct exposure of an open wound to infected blood."
That's why Greg Louganis's blood in the Olympic pool posed about zero risk. The blood was diluted by thousands of gallons of water, and "chlorine kills HIV," says Dr. John Ward, chief of HIV-AIDS surveillance at the U.S. Centers for Disease Control and Prevention. Also, skin is a very effective barrier to HIV; only a diver with an open wound would face any risk. "If the virus just touches the skin, it is unheard of for it to cause infection: the skin has no receptors to bind HIV," explains Fauci. And unlike cold and flu viruses, a retrovirus like HIV cannot survive outside a body; it must insinuate itself into a cell's genes.
Even violent sports pose little threat of HIV. A new study in the Annals of Internal Medicine, for instance, finds that in professional football, where there are almost four bleeding injuries per game, the risk of HIV transmission is less than 1 in 1 million. (The risk from unprotected sex with a woman is greater than 1 in 400.) Pro-basketball players run little risk, either: there are HIVs in saliva and sweat, but too few to pose a threat of infection. As for splattered blood, out of 19.5 million cases of HIV infection worldwide, two are known to have been caused by bloody fistfights.
The Olympic committee does not test for HIV, and it has science on its side. The risk of acquiring HIV in sports is so low that "[HIV-positive] athletes need not be excluded from participation," write the CDC's Dr. Eric Mast and colleagues in an Annals paper. Only in a sport with extensive skin-to-skin contact (like wrestling) should referees disqualify an athlete with an open sore, they say. But there are no refs at postgame parties.