Health officials are sounding the alarm over a potential measles exposure at Chicago O’Hare International Airport.

An infected adult was mainly confined to the airport’s Terminal 1 area, potentially exposing hundreds of others to the world’s most infectious disease.

The person was at the airport – the world’s fourth busiest in terms of passenger numbers – on April 22 and April 23 between 10am and 8pm both days.

They had had one prior dose of the MMR vaccine but they went on to develop a rash on April 25 and tests confirmed they had contracted measles.

Since being being diagnosed, they have been been isolating home.

Another case was identified days later in an adult living in the same county in Illinois.

Their vaccination status is unknown, but they checked into to a local hospital for treatment on April 28 and medical staff quickly isolated them.

Officials are warning anyone who fears they may have been exposed to contact their health provider and monitor for symptoms in what is the latest in a string of measles scares to rock America’s major airports and surrounding neighborhoods.