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BACKGROUND: Measles is a highly infectious but vaccine-preventable viral disease with potentially severe complications (e.g., pneumonia, encephalitis, subacute sclerosing panencephalitis, and death). Immunization initiatives led to measles elimination in the United States in 2000, but the disease is still prevalent globally. Decreasing vaccination rates pose a public health risk. We present an unusual co-occurrence of measles clusters linked to at least three distinct introductions to Hawaii within a 2-month period.
METHODS: On October 14, 2014, the Hawaii Department of Health (HDOH) was notified of a cluster of suspect measles cases on the island of Kauai; in the subsequent 5 weeks, HDOH was notified of cases of suspect measles on Maui as well as on Oahu. Serological and PCR assays for evidence of measles infection were performed; available specimens were sent to CDC for genotyping. Epidemiologic investigations and contact tracings were initiated. Prophylaxis was provided when indicated.
RESULTS: HDOH identified 13 confirmed cases, all of whom were Hawaii residents: Maui (4), Kauai (7), and Oahu (2). Except for one infant (aged 6 months), all were adults (18–53 years, median adult age 34). Of the 13 cases, eight were unvaccinated. Epidemiologic investigation revealed at least three separate introductions to the state: 1) unvaccinated travelers to Indonesia and Malaysia on Kauai, 2) an unvaccinated traveler to the Philippines on Maui, and 3) a traveler to Disneyland (Los Angeles, California) on Maui. One Oahu case did not have identifiable epidemiologic risk factors, and the other traveled to Maui and Kauai during the infectious periods for those clusters. Genotype B3 was identified in the Maui traveler to the Philippines, D8 in the Kauai travelers to Indonesia and Malaysia, and D8 in the Maui traveler to California.
CONCLUSIONS: Our recent experience demonstrates that the risk of measles introduction persists. Disease spread in these outbreaks was limited, likely attributable to generally high vaccination rates in Hawaii (93% of 19–35 month-olds; 90% of 13–17 year-olds in 2013) and rapid public health response. However, multiple concurrent outbreaks may become more common in this era of ready and frequent travel, especially should vaccination rates continue to fall—state data indicate a steady rise in vaccine religious exemptions over the past 6 years. Continued action by public health as well as individual clinicians is needed to emphasize the importance of vaccination, particularly in areas where vaccination rates are much lower than the state average.