It was not clear how much the illness had impacted the team, but several swimmers either were pulled from their events or struggled Sunday.

The United States team at the swimming world championships in Singapore is battling a case of “acute gastroenteritis” that compromised performances on the opening day of eight days of competition in the pool.

USA Swimming team members are recovering from acute gastroenteritis as they compete in the World Aquatics Championships in Singapore, a spokesperson for the team told NPR on Sunday. The team's medical staff has been "treating those experiencing symptoms and advising the team on further preventative and recovery measures,