TWO MEASLES OUTBREAKS AFTER IMPORTATION — UTAH, MARCH–JUNE 2011

Sunday, 8th of June 2014

[source]MMWR[|source]

In 2000, the last year in which an outbreak had occurred in Utah, measles was declared not endemic in the United States, but measles importations continue to occur, leading to outbreaks, especially among unvaccinated persons. Consequently, many U.S. health-care personnel have never seen a measles patient, which might hamper diagnosis and delay reporting.

 In this report, the authors describe the two outbreaks that occurred between March and June 2011, in the state of Utah. The report describes the process and findings of a collaborative investigation of the local health departments with the state health department in the state of Utah. The report documents the two measles outbreaks comprising 13 confirmed cases. More details are accessible at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6212a2.htm

 

 EDITORIAL NOTE

Because measles remains endemic in many regions of the world, the United States continues to be at risk for measles importations and outbreaks. In 2011, a total of 220 measles cases were reported in the United States, the highest number of reported measles cases since 1996; 89% were associated with importations. The outbreaks in Utah and elsewhere during 2011 highlight the critical need for appropriate vaccination of U.S. residents, particularly those who travel internationally. The Salt Lake County outbreak began when an unvaccinated traveller from the United States developed measles on returning to the United States and infected four other unvaccinated persons.

The genotype D4 sequences obtained from the two Utah outbreaks differed by a single nucleotide. Each of the Utah sequences was identical to one of two predominant sequence variants of genotype D4 that were circulating in Europe during 2011. This, together with the interval of 5 weeks without cases between the two outbreaks, suggests the second outbreak likely was the result of a separate importation from an unknown source, rather than a continuation of the first outbreak.

In the Salt Lake County outbreak, three of the patients were adolescents who acquired the disease in school. In 2010, an estimated 96.4% of children attending public school in Utah were vaccinated with 2 doses of MMR vaccine. The high level of vaccination coverage among schoolchildren likely helped contain this outbreak. None of the three patients infected by the index patient at school transmitted the disease to other students. Ensuring high vaccination rates among schoolchildren is important to limit measles transmission.

For patients with risk factors for measles (e.g., unvaccinated status, recent travel history, or known epidemiologic link to a confirmed measles case), health-care providers and public health officials should consider measles in the differential diagnosis of febrile rash illness and should consider other potential exposures, including parvovirus, when ordering laboratory tests. Because measles now occurs so rarely in the United States, interpretation of measles tests can be challenging, especially during outbreaks, and confirming and correctly classifying measles in vaccinated persons can be particularly difficult. False-positive measles IgM results might be obtained in response to infections caused by parvovirus and other viruses, including enteroviruses, Epstein-Barr virus, and varicella zoster virus. The capture IgM assay methodology available at CDCs Measles Virus Laboratory generally is less prone to nonspecific reactions; however, the low prevalence of measles in the United States results in a low positive predictive value regardless of the IgM assay used. Serum and respiratory specimens both should be collected from suspected patients at first contact, because serological testing coupled with molecular testing provides the best opportunity for laboratory confirmation.

Measles cases and outbreaks can have considerable impact on communities in the United States and often require substantial resources for public health response. Recognition of suspected measles cases by health-care providers and immediate reporting to public health officials can help limit illness and associated costs. For the two Utah outbreaks combined, those costs were estimated from multiple sources to exceed $330,000 for public health personnel time at state and local levels, vaccine administration, laboratory testing, and outbreak control efforts. Unvaccinated persons put themselves and their communities at risk for measles. Maintaining high vaccination coverage and rapid public health response is critical to ensuring continued measles elimination in the United States.