Health officials have issued a warning about possible measles exposure at Chicago’s O’Hare International Airport. The alert has raised concerns due to the highly contagious nature of the disease.

According to authorities, an infected individual spent several hours in Terminal 1 on April 22 and 23 between 10 a.m. and 8 p.m. This time frame means hundreds of travelers may have been exposed.

The patient had previously received one dose of the MMR vaccine, which provides some but not full protection. Despite that, they developed symptoms including a rash that appeared on April 25.

Testing later confirmed the case as measles. The individual is now isolating at home while public health officials trace contacts and monitor for additional infections.

Just days after this case was confirmed, a second measles infection was reported in the same Illinois county, adding urgency to the investigation. Officials have not yet determined if the cases are linked.

Measles spreads through coughing and sneezing and can linger in the air for up to two hours. Even brief contact in enclosed spaces like airports can lead to transmission.

Doctors emphasize that vaccination remains the best protection. Two doses of the MMR vaccine are about 97% effective at preventing measles. Those unsure of their vaccination status are urged to check records and, if necessary, get vaccinated.

Health officials are asking anyone who was in Terminal 1 during the exposure period to watch for symptoms such as fever, cough, runny nose, red eyes, and rash. Anyone who develops signs is advised to contact a healthcare provider immediately before visiting a clinic to avoid further spread.