Mumps is caused by a virus. In children, mumps is usually a mild disease. Adults may have more serious disease and more complications.
Due to good immunization coverage, mumps is now rare in the United States. An estimated 212,000 cases occurred in 1964, while only 258 cases were reported in 2004. In 2006, outbreaks of mumps occurred in 45 states and the District of Columbia, primarily on college campuses. During January 1-October 7, 2006, 5,783 confirmed or probable cases of mumps were reported to CDC.