Mumps (Infectious Parotitis)

Current Case Definition for Surveillance

The current clinical case definition for mumps is: "An illness with acute onset of unilateral or bilateral tender, self-limited swelling of the parotid or other salivary gland, lasting two or more days, and without other apparent cause." Laboratory confirmation requires the isolation of mumps virus from a clinical specimen, or a significant rise in mumps antibody level by any standard serologic test, or a positive serologic test for mumps IgM antibody. Probable cases meet the clinical case definition but are not laboratory confirmed or epidemiologically linked to another case. Confirmed cases are either laboratory confirmed, or meet the clinical case definition and are epidemiologically linked to another probable or confirmed case. In Maryland, mumps cases are rarely investigated by health departments. Thus, all reports of mumps from health professionals are counted as probable cases and transmitted to the CDC.

Immunization

A killed vaccine providing only short-lasting immunity was licensed in 1948 and used until the mid 1970's. A live vaccine was licensed in 1967. The currently used live vaccine elicits antibody in over 90% of vaccinees, and produces durable, effective immunity. The mumps vaccine has been combined with the measles and rubella vaccines as MMR since 1971. Immunization was required by Maryland regulation for children entering pre-school programs for the first time in 1992. In 1994 mumps vaccine was required for entrance to kindergarten, and grades 1, 2, 6, 7, and 8. The requirement for entry into other grades is being phased in. Based on the 1993/94 retrospective kindergarten survey, an estimated 86% of children in Maryland had received one dose of MMR by 24 months of age (compared to 78% in the 1988/89 survey), and 99% had received at least one dose by age 60 months.

Historical Trends

In the pre-vaccine era in the United States, outbreaks of mumps occurred in two to seven year cycles. In Maryland, there was extreme year-to-year fluctuation in the number of reported mumps cases from 1920 through the 1970's. There was also a steady decline in the five year mean incidence of mumps in Maryland from the early 1930's through the early 1980's.

Epidemiology, 1988 - 1993

Although mumps is generally less serious than several of the other vaccine preventable diseases, testicular inflammation, frequently requiring hospitalization, occurs in up to 38% of postpubertal males, and central nervous system involvement occurs in 3.5 per 1,000 reported cases. In 1990, the peak year of a mumps epidemic in Maryland, the state reported 22% of all cases reported in the entire United States. During the six year period, 73% of all reported cases were among school age children. The incidence was also dramatically higher in 5 to 19 year olds than in other age groups, with the lowest incidence in infants and in adults over 19 years of age. According to the CDC, "the total number of mumps cases reported in 1993-1,692-was the lowest number ever reported in the United States."