Outbreak of measles in the Republic of Korea, 2007: Importance of nosocomial transmission

Background. From 2002 through 2006, Republic of Korea conducted extensive measles elimination activities and declared elimination in 2006. An outbreak of measles involving 180 confirmed cases occurred during 2007. Methods. An outbreak investigation was performed and enhanced surveillance was implemented. Detailed case investigations and laboratory testing included serologic and molecular diagnostic methods. Cases were classified according to World Health Organization and national guidelines. Results. During 2007, 451 suspected cases were reported and 180 (40%) cases were confirmed as measles during epidemiologic weeks 14-42. Incidence during the outbreak was 3.7 cases per million persons, excluding imported cases. Most confirmed cases were reported from Seoul; 137 (76%) cases were among children <24 months old, 124 (69%) case patients had no history of measles vaccination, and 81 (45%) case patients resulted from nosocomial transmission in 6 hospitals. Community members, patients, and health care workers all contributed to measles virus transmission. Limited outbreak control measures were implemented; high population immunity likely accounted for the self-limited transmission during this outbreak. Conclusions. Limited outbreaks of measles, in which nosocomial transmission can play an important role, may occur after countries have declared elimination. Timely and opportunistic vaccination may help prevent such outbreaks; high-quality surveillance is critical for their detection.