Health officials are warning of possible measles exposure at Chicago O’Hare Airport after an infected adult spent April 22–23 in Terminal 1 between 10 a.m. and 8 p.m. The person, who had one MMR vaccine dose, developed a rash by April 25 and is now isolating.

Measles is highly contagious and can linger in the air for up to two hours. A second case has since been confirmed in the same Illinois county, with contact tracing underway.

Officials urge anyone at O’Hare during those times to check their vaccination status and contact a healthcare provider if unvaccinated or unsure. Measles can lead to serious complications, especially for children, pregnant women, and the immunocompromised.