Chicago health officials say they’ve confirmed a measles case and are working to contact those who may have been exposed to the infection.

The Chicago Department of Public Health said Saturday they confirmed the case Friday and exposures may have occurred on Thursday and Friday at O’Hare International Airport and in downtown Chicago. Officials say those who think they may have been exposed should check with their health care providers to see if they were vaccinated or need a vaccination.

This is at least the second confirmed case in Cook County since March when public health officials confirmed a case in the northern Chicago suburbs.

The confirmations come amid an ongoing measles outbreak in the U.S.

Experts say Chicago has one of the highest measles vaccination rates in the nation.