Notes from the Field: Measles Outbreak — Cook County, Illinois, October–November 2023

On October 10, 2023, the Cook County Department of Public Health (CCDPH) in Illinois was notified by hospital A, a large pediatric facility, of a suspected measles case in a child aged 2 years (patient A) who had immigrated from Yemen on September 29 and who had no history of receipt of measles, mumps, and rubella (MMR) vaccine.The child visited hospital A's emergency department (ED) on October 5 with fever, cough, and coryza and, after receipt of negative COVID-19, influenza, and respiratory syncytial virus test results, received a diagnosis of an unspecified viral illness.On October 8, the child visited hospital B's ED with worsening respiratory symptoms and received a positive rhinovirus/enterovirus test result on a respiratory pathogen panel, after which the child was transferred to hospital A and admitted for respiratory distress related to bronchiolitis and underlying reactive airway disease.The next day, while hospitalized, the child developed a maculopapular rash.On October 10, the child's family reported contact with a person with clinically diagnosed measles before U.S. arrival.*Measles was confirmed by real-time reverse transcription-polymerase chain reaction (RT-PCR) testing on October 11; the child was discharged the same day.