SPRINGFIELD, Ill. — Public health officials are reporting a second case of measles in a person who was at Chicago’s O’Hare International Airport, the nation’s third-largest airport by passenger volume.

The Illinois Department of Public Health said Wednesday that the case is unrelated to one reported last week. The department said there’s no measles outbreak at O’Hare, which served 78 million passengers in 2016.

Officials say the individual with the second confirmed case was at the airport Jan. 9. Authorities said local health departments are contacting people believed to be most at risk, including passengers on the inbound flight to Chicago. The individual also was at locations in suburban Chicago.

Measles is easily spread through the air when someone coughs or sneezes. Experts say people who think they may have been exposed should contact their health care provider.