Sports is about more than showering with other people.

The U.S. Centers for Disease Control revealed today that 21 players on 13 pro basketball teams were sickened with norovirus last fall.

The federal researchers didn’t name the teams. But media reports have said players with a stomach bug at the time included four on the Orlando Magic, including star center Dwight Howard.

The virus can spread through the air on the basketball court. But researchers said it more likely was spread by players socializing.

Whatever that means.

Dr. Rishi Desai, one of the CDC investigators, said it’s not clear how the outbreak started, but the strain of norovirus was an unusual enough that investigators believe players got it from each other rather than from family members or others.

CDC officials believe that there may have been at least two instances in which an infected team passed it to a healthy team. The CDC recommended that in the future, NBA players sick with the virus should not play or take part in team activities.