Police in Santa Barbara, California, are investigating after nearly 30 people had to seek medical care at a half-marathon running event held in the city on Sunday.
In a statement provided to the BBC's US partner CBS News, officers said they received a report from Santa Barbara Cottage Hospital about race participants who sought medical treatment "for unusual symptoms" after the race ended.
"The cause of the reported symptoms has not been confirmed," the statement added.
Cottage Health, which operates the hospital, told CBS it had seen "a larger than expected number of emergency visits" from those who ran the race.
"There is no specific action recommended for the public at this time; however, participants who feel unwell should seek medical attention and follow guidance from healthcare professionals," police said.
Cottage Hospital said it treated 27 people from the half marathon at emergency rooms in Santa Barbara and the nearby city of Goleta.
The vast majority of them - 24 - were discharged after treatment, while three people were still in hospital as of Monday in stable condition.
Several thousand people ran the half marathon on a hotter-than-usual day in Santa Barbara along the Pacific Ocean. Temperatures reportedly reached 86F (27C) by midday, compared to a typical early November temperature of low 70s.
