Measles - United States, 2011.

In 2000, the United States achieved measles elimination (defined as interruption of year-round endemic measles transmission). However, importations of measles into the United States continue to occur, posing risks for measles outbreaks and sustained measles transmission. During 2011, a total of 222 measles cases (incidence rate: 0.7 per 1 million population) and 17 measles outbreaks (defined as three or more cases linked in time or place) were reported to CDC, compared with a median of 60 (range: 37-140) cases and four (range: 2-10) outbreaks reported annually during 2001-2010. This report updates an earlier report on measles in the United States during the first 5 months of 2011. Of the 222 cases, 112 (50%) were associated with 17 outbreaks, and 200 (90%) were associated with importations from other countries, including 52 (26%) cases in U.S. residents returning from abroad and 20 (10%) cases in foreign visitors. Other cases associated with importations included 67 (34%) linked epidemiologically to importations, 39 (20%) with virologic evidence suggesting recent importation, and 22 (11%) linked to cases with virologic evidence of recent importation. Most patients (86%) were unvaccinated or had unknown vaccination status. The increased numbers of outbreaks and measles importations into the United States underscore the ongoing risk for measles among unvaccinated persons and the importance of vaccination against measles.