Misdiagnoses: Delayed Identification of a Measles Outbreak Associated with Unvaccinated Children and a Daycare – Kansas 2011

BACKGROUND: Before 1963, more than 500,000 measles cases were reported annually in the United States.  Through vaccination and control efforts United States declared endemic measles as eliminated in 2000; imported cases of measles continue and can lead to outbreaks, especially in unvaccinated populations.  Many health-care providers have never seen a case of measles which may hamper diagnosis and delay reporting. On April 25, 2011 Kansas Department of Health and Environment was notified by Johnson County Health Department of measles in an unvaccinated child. Outbreak and contact investigations were initiated; prevention and control measures were implemented.  

METHODS: Investigation included current and retrospective case finding.  Patients were interviewed using a standardized questionnaire.  Cases were classified according to CSTE case definition.  Contacts were determined for cases not retrospectively identified and assessed for vaccination status.  Unvaccinated contacts were excluded from school.  Testing for measles IgG, IgM, and polymerase chain reaction (PCR) were performed.  

RESULTS: Seven confirmed measles cases were identified, including four daycare attendees, one unvaccinated child who visited the daycare (initial patient reported as a measles case) and her two unvaccinated siblings.  All daycare attendees had illnesses consistent with measles, were misdiagnosed with other illnesses, and were retrospectively identified; three were hospitalized and one sought outpatient care from a health-care provider.  All children had rash, fever, cough, and coryza; five had conjunctivitis.  Rash onset date ranged from March 23 to April 30.  Days from onset of symptoms to diagnosis of measles ranged from three to 368 days (median: 55 days).  Four were too young to be vaccinated; three were unvaccinated because of religious exemption. Three were PCR positive (genotype D4), one was also IgM positive, and three were IgG positive; one was not tested but had symptoms consistent with measles. Two infants with earliest rash onset dates were index cases for infants at the daycare and for one other unvaccinated child; because of these delays in diagnosis (66 and 368 days) their source of infection was not identified.  

CONCLUSIONS: Physician misdiagnosis caused a significant delay in identifying cases associated with this outbreak resulting in missed opportunities to implement control measures. A definitive source was not identified; virologic evidence suggests that these cases are likely linked to an undetected case or cases from the WHO European region, which reported over 30,000 cases of measles in 2011.  Health-care providers should maintain a heightened awareness of measles in unvaccinated children with a febrile rash illness and clinically compatible measles symptoms.