Outbreak of Measles Associated with a Cook County, IL Child Care Center, January-February 2015

BACKGROUND:  The United States is in the midst of a measles outbreak that has resulted in nearly 180 cases and has extended to 17 states.  In January 2015, 2 cases of measles were identified in suburban Cook County, IL and an outbreak investigation was initiated by the Cook County Department of Public Health.

METHODS:  A confirmed case was defined as acute febrile rash and 1) laboratory confirmation of measles, or 2) epidemiologic linkage to a laboratory confirmed case in an Illinois resident. Contact tracing was performed for each confirmed case.  Individuals susceptible to measles were monitored for 21 days after their last measles exposure.  Control measures included isolation of cases while infectious, exclusion of susceptible contacts from high-risk settings, coordination of community vaccination clinics, and provision of post-exposure prophylaxis to contacts when applicable. 

RESULTS:  Fifteen measles cases were identified; 12 (80%) in infants < 12 months and 3 (20%) in adults with unknown vaccination history.  The median age was 8 months (range: 3 months – 41 years). All 12 infants and 1 adult were directly associated with a single child care center and the other two adults resided in the same geographic area as this center.  An infant was the index patient at the child care center, leading to an 86% attack rate among infants in attendance. Measles was not recognized in this infant while symptomatic; the infant was hospitalized to rule out Kawasaki disease and later diagnosed with measles by serology. Identified exposure settings included places of employment, pediatric clinics, and grocery stores.  Six (50%) infants had a total of 11 pediatric clinic visits while infectious, potentially exposing over 180 children and staff.  Measles vaccination records for employees at the child care center and pediatric clinics were not readily available. Sixty-six individuals exposed at pediatric clinics were monitored; none developed disease.

CONCLUSIONS:  A majority of the cases in this measles outbreak occurred among infants < 12 months, a population for whom vaccination is not routinely recommended. This outbreak highlights the potential for infants to transmit measles, the importance of screening for airborne infectious diseases at outpatient clinics, and the need for healthcare and child care workers, as well as others with regular contact with vulnerable populations to be properly vaccinated with documentation readily available to their employers.