Peter Schade, the Erie County health commissioner, said he met Wednesday morning with members of the group, who were part of the advance team for California’s delegation to the convention. Schade said investigators do not yet know how the staffers contracted the severe gastrointestinal bug, but they believe the chain of transmission started in California.

“It came with them,” Schade said.

Health officials are now taking food histories from those who had fallen ill — and are staying at a resort hotel about an hour outside of Cleveland — to try to pinpoint the cause.

“We’re asking, ‘What did you guys do? Did you do anything together before you came out?”’ Schade said.