CHICAGO (CBS) — The Illinois Department of Public Health is warning anyone who might have been at Midway International Airport last Friday night that they might have been exposed to measles.

An unvaccinated passenger who had measles arrived on a flight at Concourse B between 9 p.m. and midnight last Friday night. The passenger later showed up in the emergency room at Northwestern Medicine Delnor Hospital in Geneva on Sunday.

Health officials said anyone who was at Midway between 9 p.m. and midnight on Feb. 22, or who was in the emergency room at Delnor between 11:45 a.m. and 2:15 p.m. on Feb. 24 might have been exposed to measles. Anyone who was at Delnor from 4 p.m. to 6:15 p.m. on Feb. 24, or from 10 a.m. to 1 p.m. on Feb. 25 also might have been exposed.

Measles is highly contagious and can be spread through the air, such as from coughing or sneezing.

“Most people are vaccinated routinely in childhood and are not at high risk. Of most concern are people who have not been vaccinated. Individuals who think they have been exposed should check with their health care provider about protection through prior vaccination or the need for vaccination,” IDPH stated.

Anyone who was infected could develop symptoms as late as March 20. Symptoms of measles include rash, high fever, cough, runny nose, and red watery eyes. If you think you have measles, you should call or email your doctor before going to their office or the emergency room.

Severe cases of measles can cause pneumonia and encephalitis (swelling of the brain).