Health officials are warning about possible measles exposure at Chicago O’Hare International Airport. An infected adult spent time in Terminal 1, potentially exposing many people to what is described as “the world’s most infectious disease.”

The individual was at the airport on April 22 and April 23, between 10am and 8pm both days. The airport is noted as “the world’s fourth busiest in terms of passenger numbers,” raising concern about how many travelers may have been affected.

The person had received one dose of the MMR vaccine but later developed symptoms. They “went on to develop a rash on April 25,” and tests confirmed measles. After diagnosis, they have been isolating at home.

A second adult case appeared in the same county in Illinois. Their vaccination status is unknown. They sought medical care on April 28, and hospital staff “quickly isolated them” to prevent further spread.

Officials urge anyone who may have been exposed to contact a healthcare provider and monitor symptoms. This is “the latest in a string of measles scares to rock America’s major airports and surrounding neighborhoods,” highlighting ongoing public health concerns.