Measles: United States, January--May 20, 2011.

Measles is a highly contagious, acute viral illness that can lead to serious complications and death. Endemic or sustained measles transmission has not occurred in the United States since the late 1990s, despite continued importations (1). During 2001--2008, a median of 56 (range: 37--140) measles cases were reported to CDC annually (2); during the first 19 weeks of 2011, 118 cases of measles were reported, the highest number reported for this period since 1996. Of the 118 cases, 105 (89%) were associated with importation from other countries, including 46 importations (34 among U.S. residents traveling abroad and 12 among foreign visitors). Among those 46 cases, 40 (87%) were importations from the World Health Organization (WHO) European and South-East Asia regions. Of the 118, 105 (89%) patients were unvaccinated. Forty-seven (40%) patients were hospitalized and nine had pneumonia. The increased number of measles importations into the United States this year underscores the importance of vaccination to prevent measles and its complications.