Health officials are issuing a warning after a confirmed measles case at Chicago O’Hare International Airport may have exposed hundreds to the highly contagious virus. The infected adult spent extended time in Terminal 1, raising concerns due to the airport’s status as one of the world’s busiest travel hubs.

The individual was present in Terminal 1 on both April 22 and April 23, between 10 a.m. and 8 p.m. each day. Though they had received one prior dose of the MMR (measles, mumps, rubella) vaccine, they developed a rash by April 25 and later tested positive for measles.

Following the diagnosis, the individual began isolating at home to reduce further risk of spreading the disease. Measles is considered one of the most infectious diseases worldwide, and even brief contact in crowded areas like airports can lead to transmission, especially among unvaccinated or partially vaccinated people.

Shortly after the first case, a second measles case was identified in an adult living in the same Illinois county. This individual sought treatment at a local hospital on April 28. Their vaccination status remains unclear, but hospital staff quickly took precautions and placed the patient in isolation.

Health officials are urging anyone who was in O’Hare’s Terminal 1 during the potential exposure window to remain alert for symptoms and contact a healthcare provider if they believe they were exposed. Measles symptoms typically begin with fever, cough, runny nose, and red eyes, followed by a rash that starts on the face and spreads.

This incident adds to a growing list of recent measles scares at major U.S. airports and surrounding areas, underscoring the importance of full vaccination. Officials stress that ensuring up-to-date immunization is the most effective defense against the resurgence of this preventable disease.