WATCH: How to avoid measles
According to the Illinois Department of Public Health, an Illinois resident with a confirmed measles diagnosis was on a flight that arrived in Concourse B at Midway Airport on February 22. The passenger was unvaccinated and infectious on that day.
"That person has contaminated hundreds or thousands of people at Midway Airport," said Dr. Robert Murphy, professor of infectious diseases at Northwestern University Medical School. "For about four days before the person feels sick, they're contagious."
Dr. Murphy said there are now five people contaminated with measles in Illinois.
People may have been exposed to measles if they were at Midway on February 22, 2019, between 9 p.m. and midnight, health officials said. Local health officials are working to notify Illinois residents who were on the affected person's flights.
The patient later sought treatment at Northwestern Memorial Delnor Hospital on February 24, 2019. People who were in the emergency department between 11:45 a.m. and 2:15 p.m. also may have been exposed to measles, as well as individuals who were in Delnor Hospital from 4 p.m. to 6:15 p.m. on February 24 and from 10 a.m. to 1 p.m. on February 25.
Health officials said these are the only known public locations in Illinois where measles exposures occurred. If infected, individuals could develop symptoms as late as March 20, 2019. Symptoms include rash, high fever, cough, runny nose and red, watery eyes.
While measles is a highly contagious disease, most people are vaccinated routinely in childhood and are not high risk, health officials said. People who have not been vaccinated are of most concern.
"They're not taking it for religious reasons or personal reasons, not for any real medical reason," Dr. Murphy said.
If you develop symptoms of measles, health officials recommend you call or email a health care providers before going to a medical office or emergency room as special arrangements can be made to protect other patients and medical staff from possible infection.