Current Trends Measles -- United States, First 26 Weeks, 1985

Through December 28, 2,704 measles cases in the United States were reported to the MMWR for 1985. Results of detailed analyses are available for cases reported during the first 26 weeks, when a provisional total of 1,802 cases was reported, a 2.4% increase over the 1,759 cases reported during the same period in 1984 (1). The overall incidence rate in both years was 0.8 cases per 100,000 population for the 26-week period. Eight states accounted for 1,333 (73.9%) cases: Illinois (259 cases), Texas (236), Arizona (194), California (143), Montana (139), Idaho (126), New York (124), and Massachusetts (112). Ten states had incidence rates greater than 1/100,000 population: Arizona, Hawaii, Idaho, Illinois, Maryland, Massachusetts, Montana, Texas, West Virginia, and Wisconsin. During the first half of 1984 and 1985, 19 and 20 states, respectively, reported measles cases (indigenous or imported). For each year, 2.5% of the nation's 3,139 counties reported measles cases during the period.

Detailed information was provided to the Division of Immunization, Center for Prevention Services, CDC, on 1,801 of the cases reported during the first 26 weeks of 1985. Of these, 1,750 (97.2%) met the standard case definition for measles,* and 661 (36.7%) were serologically confirmed. In most cases (72%), onset of rash occurred between weeks 8 and 20 (weeks ending February 23 and May 25, respectively). There was a biphasic distribution of cases during this period (Figure 1).

In the first half of 1984, the highest incidence rate was reported among children 10-14 years of age (Table 1). By comparison, in the first half of 1985, the highest incidence rate was reported among 15- to 19-year-olds (3.1/100,000), followed by preschool-aged children (2.5/100,000). The incidence rate among 10- to 14-year-olds decreased from 2.9/100,000 in 1984 to 1.8/100,000 in 1985. Of the 466 preschool-aged children with measles, 137 (29.4%) were infants under 1 year of age; 81 (17.4%) were 12-14 months of age; 24 (5.2%) were 15 months of age; and 224 (48.1%) were 16 months-4 years of age.

Of the 1,256 (69.7%) patients for whom the setting of transmission was reported, 903 (71.9%) acquired measles in school**; 126 (10.0%), at home; 63 (5.0%), in medical settings; 41 (3.3%), in daycare centers; 18 (1.4%), in church, and 105 (8.4%), in a variety of other settings, including sporting events and summer camp.

Seventy cases (3.9%) were international importations. An additional 128 (7.1%) cases were epidemiologically linked to an international importation within two generations of infection. Therefore, 198 (11.0% of all cases) were classified as international importations during this period (2).

Vaccination status of patients in 1984 and 1985 was similar. Of the 1,801 cases reported during the first 26 weeks of 1985, 859 of the patients had been vaccinated on or after the first birthday; 247 had been vaccinated at 12-14 months of age (Table 2). A total of 846 measles patients were unvaccinated, and 96 had histories of inadequate vaccination (vaccinated before the first birthday).

Of the 1,801 cases, 466 (25.9%) were classified as preventable (2) (Table 3). The highest proportion of preventable cases occurred among persons who were not of school age: 69.2% of cases among children 16 months-4 years of age were preventable. Only 20.4% of cases among persons 5-19 years of age were preventable; however, 47.0% of all preventable cases occurred in this age group.

Of the 1,335 persons with nonpreventable cases, 242 (18.1%) were too young for routine vaccination (under 16 months of age), and 42 (3.1%) were too old (born before 1957) (Table 4). Of the 1,051 who were between 16 months and 28 years of age, 842 (80.1%) had been vaccinated on or after the first birthday; 11 (1.0%) had a prior physician diagnosis of measles; 34 (3.2%) were not U.S. citizens; and 163 (15.5%) had medical contraindications or exemptions under state law. One person (0.1%) had laboratory evidence of immunity. Reported by Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: In the prevaccine era, an average of 500,000 measles cases was reported each year (3). After measles vaccine was licensed in 1963, the incidence of measles markedly declined. Since 1981, the number of reported measles cases has remained relatively constant: 3,124 in 1981, 1,714 in 1982, 1,497 in 1983, and 2,534 in 1984. The number of cases reported during the first half of 1985 is similar to that reported during the first half of 1984 (1). As in recent years, measles was geographically restricted: 97.5% of the nation's counties were free of measles during this period.

While incidence rates during the first 26 weeks of 1984 and 1985 were comparable, there were differences in the age characteristics of patients. In 1984, persons 10-14 years of age accounted for approximately 29% of cases, compared with only 18% of cases in 1985. The incidence rate for 15- to 19-year-olds was higher in 1985. Over a third of measles patients were in this age group, due in part to the large number of outbreaks on college campuses in 1985 (4). Colleges and universities are now beginning to require evidence of immunity to measles for matriculation; this requirement should result in a decrease in measles in this population.

As the measles elimination strategy is successfully implemented, the proportion of preventable cases should decrease. The decrease in the percentage of preventable cases from 34.6% in 1984 (1) to 25.2% during the first half of 1985 is encouraging. As in 1984, preschool-aged children over 15 months of age had the highest proportion of preventable cases. Because these children are not reached by existing school laws, greater efforts need to be directed to this age group. School-aged persons accounted for the largest percentage of all preventable cases, and schools were the setting of transmission for the majority of cases. Therefore, continued enforcement of current school immunization laws is important for further reduction of measles in the United States.

References

1. CDC. Measles--United States, first 26 weeks, 1984. MMWR 1984;33:495-6, 501-4.

2. CDC. Classification of measles cases and categorization of measles elimination programs. MMWR 1982;31:707-11.

3. CDC. Measles surveillance report no. 11, 1977-1981. Atlanta, Georgia: Centers for Disease Control, 1982.

4. CDC. Measles on college campuses--United States, 1985. MMWR 1985;34:445-9. *Fever (38.3 C (101 F) or higher, if measured), generalized rash of 3 days' or longer duration, and at least one of the following: cough, coryza, conjunctivitis. **Includes kindergarten through college.

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