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BACKGROUND: Though measles elimination was declared in 2000, exposures to imported cases continue to cause outbreaks in the United States. In January 2014 a person infectious with measles visited New York City (NYC) leading to an outbreak of 25 cases. The epidemiology of the outbreak was described.
METHODS: Investigation of suspected measles cases included patient interview, and medical and immunization record review. Measles IgM and IgG serology and Polymerase Chain Reaction (PCR) of nasopharyngeal swabs were performed. Measles IgG avidity was performed on a subset of cases to assess secondary immune response. Cases were classified according to the CSTE case definition. Epidemiologic, clinical, and laboratory data for outbreak cases residing in NYC were analyzed. Contacts were identified and control measures were implemented.
RESULTS: Twenty-five cases were confirmed with onset dates from February 5 through April 11, 2014. Eleven (44%) cases were <18 years of age and 14 (56%) were adults (19 years and older); cases ranged in age from 3 months to 63 years (median 22 years). Eight (32%) cases were unvaccinated, 2 (8%) had received 1 dose of measles-containing vaccine, 5 (20%) had received 2 doses and 10 (40%) had unknown vaccination status. All cases were confirmed by positive measles IgM or PCR. Six cases with 2 doses of measles-mumps-rubella vaccine (MMR) or unknown immunization history were IgM negative and IgG positive ≤72 hours of rash onset, but PCR positive. Among all 13 cases tested for avidity that had 2 MMRs or unknown vaccination history, 11 (85%) had high avidity. Providers did not initially suspect measles in 4 (16%) cases and suspected measles for 5 (20%) cases but did not report to the Health Department within 24 hours. Over 1,700 contacts were identified. Control measures included administration of immunoglobulin or MMR post-exposure prophylaxis and home isolation of susceptible contacts. Alerts were sent to providers, and the Health Department developed and distributed posters for healthcare facilities. Active notification and vaccination of unvaccinated infants >12 months and an early second routine dose of MMR for patients aged <4 years presenting for care was recommended to providers in the six most affected zip codes.
CONCLUSIONS: A lack of suspicion of measles and reporting delays led to delays in control measures. This outbreak highlighted the importance of PCR testing for measles diagnosis, particularly early in the course of illness and in previously vaccinated people. High population-level immunity likely prevented a much larger outbreak.