CCDPH said this is the third case in suburban Cook County this year.
Officials said an adult, whose vaccination status is unknown, tested positive for measles.
Public health officials believe the adult contracted measles after a sick child traveled through O'Hare airport last month.
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The infected person was at the Aldi grocery store at 4820 Cal Sag Road in Crestwood, Illinois.
Anybody who shopped at the store on Wednesday, September 24 between 5 p.m. and 7:30 p.m. might have been exposed.
Measles symptoms appear up to 21 days following exposure.