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.

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 is still recovering after suffering an outbreak of acute gastroenteritis ahead of the swimming world championships in Singapore that began on Sunday, a spokesperson told Reuters.