Norovirus has gone on the offensive in cruise ships, conventions and other places where people congregate, and now this bad bug has taken a shot at the National Basketball Association. 

A report Monday from the Centers for Disease Control and Prevention, published in Clinical Infectious Diseases, recounts the only known norovirus outbreak within professional sports. According to the CDC, 21 players and 3 staff members from 13 different NBA teams in 11 states passed around norovirus from Nov. 28 to Dec. 8, 2010. 

The CDC began investigating Dec. 9, trying to determine the extent of the outbreak and how the virus was transmitted as the affected teams played 49 games against one another.

None of the baseketball players admitted playing while ill, but one acknowledged vomiting near teammates on the way to a game, the researchers write. Three players reported traveling with or having direct interactions with ill teammates. Some said they became ill within 72 hours after playing a game with teams that had lab-confirmed cases of norovirus infection.

Twenty-two percent of the case subjects reported ill family members, but some healthy players with no one ill at home got sick shortly after they were exposed to ill players from another team, suggesting both person-to-person and team-team transmission.

And while this was the first documented norovirus outbreak within professional basketball, it likely wasn’t actually the first. After looking over NBA reports for the past 10 years, the CDC researchers concluded that gastrointestinal ailments were second only to game-related injuries for players sitting out a game for medical reasons.

Norovirus is not only awfully contagious but just plain awful, causing its victims to suffer diarrhea, vomiting, fever, body aches and severe stomach cramps. Infected people can shed billions of infectious doses and the bug can aerosolize when it’s vomited. It persists on surfaces and is resistant to common disinfectants, the CDC points out.

“All of these factors may contribute to the rapid spread of norovirus among teammates who spend long periods together in closed spaces while in transit, during training sessions, in locker rooms, and during games,” the CDC researchers wrote. “In this investigation, ill players reported vomiting near other teammates, traveling and interacting with healthy teammates while they were ill, and participating in games while they were still ill or within 24 hours of recovery when they were likely still infectious.”

To help limit transmission, the CDC report suggests restricting player activities and interactions not only during the acute illness phase but also shortly after recovery. Once people recover from norovirus symptoms, most will remain contagious for another 24 to 72 hours.

The CDC researchers also recommended “strict hygiene,” including thorough hand washing with soap and running water (preferable to using hand sanitizers, they say) and disinfecting common areas, like locker rooms, with sodium hypochlorite solution.

There’s no effective treatment for norovirus and while a vaccine is in the works, it isn’t available yet.  The CDC estimates that norovirus causes 21 million gastic illnesses each year in the U.S.