Implications of a 2005 measles outbreak in Indiana for sustained elimination of measles in the United States

BACKGROUND: Measles was declared eliminated from the United States in 2000 but remains endemic worldwide. In 2005, a 17-year-old unvaccinated girl who was incubating measles returned from Romania, creating the largest documented outbreak of measles in the United States since 1996. METHODS: We conducted a case-series investigation, molecular typing of viral isolates, surveys of rates of vaccination coverage, interviews regarding attitudes toward vaccination, and cost surveys. RESULTS: Approximately 500 persons attended a gathering with the index patient one day after her return home. Approximately 50 lacked evidence of measles immunity, of whom 16 (32 percent) acquired measles at the gathering. During the six weeks after the gathering, a total of 34 cases of measles were confirmed. Of the patients with confirmed measles, 94 percent were unvaccinated, 88 percent were less than 20 years of age, and 9 percent were hospitalized. Of the 28 patients who were 5 to 19 years of age, 71 percent were home-schooled. Vaccine failure occurred in two persons. The virus strain was genotype D4, which is endemic in Romania. Although containment measures began after 20 persons were already infectious, measles remained confined mostly to children whose parents had refused to have them vaccinated, primarily out of concern for adverse events from the vaccine. Seventy-one percent of patients were from four households. Levels of measles-vaccination coverage in Indiana were 92 percent for preschoolers and 98 percent for sixth graders. Estimated costs of containing the disease were at least $167,685, including $113,647 at a hospital with an infected employee. CONCLUSIONS: This outbreak was caused by the importation of measles into a population of children whose parents had refused to have them vaccinated because of safety concerns about the vaccine. High vaccination levels in the surrounding community and low rates of vaccine failure averted an epidemic. Maintenance of high rates of vaccination coverage, including improved strategies of communication with persons who refuse vaccination, is necessary to prevent future outbreaks and sustain the elimination of measles in the United States.