Current Trends Mumps -- United States, 1980-1983

As of October 22 (week 42), 1983, 2,683 mumps cases were reported to CDC, which represents a 41% decrease in mumps activity overall, compared to the same period in 1982, and a record low for reports in this period. Twenty-seven reporting areas show decreased numbers of cases for 1983. In 1980, all states reported some mumps activity; whereas in 1981, one state reported no mumps. To date in 1983, four areas are reported free of mumps, compared to three areas in the same period of 1982.

In 1982, 5,270 cases of mumps were reported to CDC, for an incidence rate of 2.3 cases per 100,000 population (Figure 1). This is 7% higher than the 1981 total of 4,941 cases, the lowest reported incidence since mumps became a nationally notifiable disease in 1968.* The small increase in 1982 was principally due to increased mumps disease in Ohio, which does not require mumps vaccination for school attendance. Ohio had almost three times as many cases in 1982 (1,775 cases) as in 1981 (687). The number of reported cases in other states decreased 17.8% between 1981 and 1982.

Age-specific data were available for 3,913 (74%) of the cases reported for 1982 (Table 1). Approximately three-fourths of mumps cases occurred among individuals under 15 years of age. The reported age-specific incidence rate in this age group decreased by 45% between 1980 (13.9/100,000) and 1982 (7.7/100,000). However, the reported incidence rate for 10- to 14-year-olds increased by 37% between 1981 and 1982, reflecting the Ohio outbreak in junior high and high school students. In contrast to 1980 and 1981, when the highest reported age-specific incidence rate occurred in 5- to 9-year-olds, in 1982, the highest rate occurred in 10- to 14-year-olds, who alone accounted for almost 40% of all patients of known age. Children 5-9 years of age had the next highest rate and accounted for 27% of cases.

The reported rate for persons 15 years of age or older also decreased between 1980 and 1982 by 13% (0.8/100,000 in 1980, compared with 0.7/100,000 in 1982) (Table 1). The small decrease was due to opposing trends in the 15- to 19-year age group versus the 20-year-and-older group. The rate in the former increased 20%, while that in the latter decreased by 40%.

The increased incidence among children 10-19 years of age between 1981 and 1982 is largely due to cases reported from Ohio, which accounted for almost one-half of all cases in this age group.

Marked declines have also been observed in the number of mumps-associated encephalitis and aseptic meningitis cases and deaths, the only complications of mumps officially reportable to CDC. There were 849 mumps-associated encephalitis cases in 1967, and seven in 1981; there were 53 mumps-associated aseptic meningitis cases in 1969, and eight in 1979))**; and there were 43 mumps-associated deaths in 1966, and two in 1980.*** The increased proportion of reported cases in older persons is also reflected in the available age-specific data on mumps-associated complications. For example, while 59% (118/200) of mumps-associated deaths occurred in persons 10 years of age or older in 1966-1975, 85% (17/20) of deaths occurred in this age group in 1976-1980 (2). Reported by Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Since mumps vaccine licensure in December 1967, more than 59 million doses of vaccine have been distributed in the United States, with an accompanying 97% decrease in reported cases (185,691 cases in 1967 versus 5,270 in 1982). Although age-specific data were available for less than 30% of U.S. cases during the first few years after vaccine licensure, trends noted in California, Massachusetts, and New York City illustrate that incidence rates have declined in all age groups by more than 90%. During 1967-1976, the highest reported rate occurred in 5- to 9-year-olds, followed by that in children under 5 years old. Together, these two groups accounted for over 70% of all reported cases. However, over the last 5 years (1978-1982), they accounted for only slightly more than 50% of reported cases. During this period, the risk of infection for 10- to 14-year-olds surpassed that for children under 5 years old. National data for 1982 indicate that the risk of infection for 10- to 14-year-olds was higher than that for any other age group.

The age-specific changes in mumps epidemiology observed since vaccine licensure are similar to those noted for measles and rubella and result from a vaccination policy oriented toward preschool and elementary schoolchildren (3). Individuals who are neither vaccinated nor infected at a young age eventually are exposed at an older age and subsequently account for the majority of reported cases. An analysis of vaccine efficacy during an Ohio outbreak confirmed that mumps vaccine is effective in preventing disease and that it does not lose its protective effect over time (4). While 95% (range 69%-99%) of school enterers in a 1982-1983 nationwide survey were found to be immunized against mumps, older children (junior and senior high school), such as those involved in a recent Ohio outbreak (4), represent the unvaccinated cohorts that still exist in many areas.

The Ohio experience illustrates the remaining susceptibility of older individuals, who are at higher risk for mumps-associated complications (1). It also demonstrates the direct and indirect costs of mumps illness--the cost associated with the 110 cases exceeded $20,000 (4). Finally, it exemplifies the twofold higher incidence rate of mumps in the 19 states (including Ohio) that do not require proof of mumps immunity for school entry, as compared to those that have such a law (34.7, compared with 17.5 cases per million population) (4).

Since mumps vaccine was licensed, it has continued to be shown to be safe and effective. A recent benefit-cost analysis noted that a mumps vaccination program, in which mumps was given as part of a measles-mumps-rubella (MMR) combination, would reduce costs associated with mumps by more than 86%, with a benefit-cost ratio of 7:1, using reported incidence rates. The program has a benefit-cost ratio of 39:1 when estimations of actual mumps incidence (to correct for underreporting) are used in the analysis (5). Since the potential for outbreaks will continue in unvaccinated cohorts, considerable medical and economic savings can be realized by including mumps immunization as part of state compulsory school immunization laws.

References

1. CDC. Mumps surveillance report. 1978.

2. CDC. Mumps surveillance report, 1977-1983 (in preparation).

3. Immunization Practices Advisory Committee. Mumps vaccine. MMWR 1982;31:617-20,625.

4. CDC. Efficacy of mumps vaccine--Ohio. MMWR 1983;32:391-2,397-8.

5. Koplan JP, Preblud SR. A benefit-cost analysis of mumps vaccine. Am J Dis Child 1982;136:362-4.

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