A Chicago resident who traveled internationally through O’Hare International Airport in early April has been diagnosed with measles, marking the first confirmed case of the disease in the city. This development comes amidst an increase in measles cases across the United States, despite the disease being declared eliminated in the country over two decades ago.
According to ABC News, the affected individual is an adult who developed a rash on April 25, leading to the measles diagnosis. The person has been isolated at their home and had previously received one dose of the measles vaccine. The Centers for Disease Control and Prevention (CDC) explain that cases where vaccinated individuals contract the disease are called breakthrough infections.
In a related occurrence, another individual from suburban Cook County also presented with measles at a local hospital, and their vaccination status remains unknown. Both cases have prompted the Chicago Department of Public Health and Cook County Department of Public Health to advise international travelers aged 12 months or older to receive two doses of the MMR vaccine at least two weeks before travel or provide other immunity evidence.
The health departments are working to trace any potential exposure at key locations, including the Chicago Public Library and various businesses and public spaces. The CDC reports 884 confirmed measles cases by April 24, 2025, across 30 jurisdictions in the U.S.
The American Society of Microbiology has noted that while measles transmission during air travel is uncommon, it remains a significant concern due to the highly contagious nature of the infection. Past incidents include cases of transmission on commercial flights in Brazil and clusters linked to air travel in the Netherlands.
Both health departments urge residents and travelers to be mindful of vaccination requirements as they continue investigating potential exposure and other related cases.
