On May 18, 2006, the U.S. Centers for Disease Control and Prevention (CDC) reported on a multi-state mumps outbreak with over 6,500 cases, which affected a number of college-aged students in the Midwest. In the U.S., the reported incidence of mumps declined after introduction of mumps vaccine in 1967 and the recommendation for its routine use in 1977.

The clinical case definition of mumps is an illness with acute onset of unilateral or bilateral tender, self-limited swelling of the parotid or other salivary gland, lasting 2 or more days, and without other apparent cause. A confirmed case of mumps is one that is laboratory confirmed or meets the clinical case definition and is linked epidemiologically to a confirmed or probable case. A case is classified as probable if it meets the clinical case definition but is neither laboratory-confirmed nor linked to another confirmed or probable mumps case. In accordance with these definitions, asymptomatic, laboratory confirmed infections were counted as confirmed cases in all states except Iowa. In Iowa, laboratory-confirmed cases that were asymptomatic or had clinical information pending, and cases for which high suspicion for mumps existed but case classification was not yet determined were classified as suspect.

To prevent mumps, the Advisory Committee on Immunization Practices recommended a 2-dose MMR vaccination series for all children, with the first dose administered at ages 12–15 months and the second dose at ages 4–6 years. Two doses of MMR vaccine were recommended for school and college entry unless the student had other evidence of immunity.