Measles Outbreak Associated with a Migrant Shelter - Chicago, Illinois, February-May 2024

Abstract

Measles, a highly contagious respiratory virus with the potential to cause severe complications, hospitalization, and death, was declared eliminated from the United States in 2000; however, with ongoing global transmission, infections in the United States still occur. On March 7, 2024, the Chicago Department of Public Health (CDPH) confirmed a case of measles in a male aged 1 year residing in a temporary shelter for migrants in Chicago. Given the congregate nature of the setting, high transmissibility of measles, and low measles vaccination coverage among shelter residents, measles virus had the potential to spread rapidly among approximately 2,100 presumed exposed shelter residents. CDPH immediately instituted outbreak investigation and response activities in collaboration with state and local health departments, health care facilities, city agencies, and shelters. On March 8, CDPH implemented active case-finding and coordinated a mass vaccination campaign at the affected shelter (shelter A), including vaccinating 882 residents and verifying previous vaccination for 784 residents over 3 days. These activities resulted in 93% measles vaccination coverage (defined as receipt of ≥1 recorded measles vaccine dose) by March 11. By May 13, a total of 57 confirmed measles cases associated with residing in or having contact with persons from shelter A had been reported. Most cases (41; 72%) were among persons who did not have documentation of measles vaccination and were considered unvaccinated. In addition, 16 cases of measles occurred among persons who had received ≥1 measles vaccine dose ≥21 days before first known exposure. This outbreak underscores the need to ensure high vaccination coverage among communities residing in congregate settings.

FIGURE

Measles cases associated with a migrant shelter (shelter A), by rash onset date and public health interventions — Chicago, Illinois, February 26–May 13, 2024 Abbreviations: CDPH = Chicago Department of Public Health; PCR = polymerase chain reaction. * Shelter A resident cases were defined as those among persons exposed while residing at Shelter A. Shelter-linked community cases were defined as those among persons exposed outside of shelter A and epidemiologically linked to a case in a shelter A resident. Shelter worker cases were defined as those among persons exposed while working at shelter A. ^† Two persons with unknown or no rash onset were included by symptom onset date. ^§ Interventions included active case-finding, vaccination events, and movement restriction.