During 1984, a provisional total of 2,534 cases of measles was reported in the United States (incidence rate 1.1 per 100,000 population) (Figure 1). This is a 69.3% increase over the 1,497 cases reported during 1983 (0.7/100,000). A total of 2,079 cases (82.0%) was reported from seven states--Texas, 602 (29.0%); Michigan, 465 (22.4%); California, 330 (15.9%); Illinois, 182 (8.8%); Washington, 172 (8.3%); New York, 165 (7.9%); and Hawaii, 163 (7.8%).

Although the overall incidence rate increased, the number of states reporting measles decreased during 1984, compared with 1983. Fifteen states reported no measles cases (indigenous or imported), compared to 12 states and the District of Columbia during the same period in 1983. Nine states were free of measles during both 1983 and 1984. In 1984, 193 (6.1%) of the nation's 3,139 counties reported measles cases, compared with 137 (4.4%) during 1983 (Table 3).

Two hundred twenty-two cases (8.8%) were associated with international or out-of-state importations, an average of 5.4 cases per week, compared with 334 cases during the same period in 1983 (1).

During 1984, detailed information was provided to CDC's Division of Immunization on 2,543 cases. The differences between this number and the 2,534 cases reported to the MMWR reflect delays in reporting.

Of 2,543 cases, 2,491 (98.0%) met the clinical case definition,* and 1,036 (40.7%) were serologically confirmed. Seasonality continued to be observed, with most onsets of rash occurring from week 9 through week 21, peaking at week 14 (134 cases) (Figure 2).

The age distribution of reported measles cases changed from 1983 to 1984 (Table 4). In 1983, the highest incidence rates were reported for preschoolers. In contrast, the rates for 1984 were highest for children 10-14 years of age; preschoolers (under 5 years of age) were the next most frequent group. Of the 622 preschoolers who had measles in 1984, 168 (27.0%) were under 12 months of age; 127 (20.4%) were 12-14 months of age; 41 (6.6%) were 15 months; and 286 (46.0%) were 16 months to 4 years of age. Persons 12-14 months of age accounted for 5.0% of the 2,543 cases.

Of the 2,543 measles patients, 1,184 (46.6%) had been vaccinated; 999 (39.3%) had been vaccinated on or after the first birthday; and 185 (7.3%) had been vaccinated before the first birthday (Table 5). A total of 1,359 (53.4%) patients were either unvaccinated or of unknown vaccination status.

Of the 2,543 cases, 874 (34.4%) were classified as preventable** (1) (Table 6). The highest proportion of preventable cases occurred among persons who were not of school age. More than 75% of the cases among children 16 months to 4 years and adults 20-24 years of age were preventable. Although more than half of the preventable cases occurred among persons 5-19 years of age, only 30.2% of cases occurring in that age group were considered preventable. The proportion of preventable cases in this age group increased progressively with increasing age.

Of the 1,669 persons who had nonpreventable measles, 336 (20.1%) were too young for routine vaccination (under 16 months of age) (Table 7). Eighty-six (5.2%) were born before 1957; vaccination is not ordinarily recommended for this group. Of the 1,247 persons 16 months to 27 years of age who acquired measles, 992 (79.6%) had been vaccinated on or after the first birthday; 24 (1.9%) had prior physician-diagnosed measles; 57 (4.6%) were international importations and were not U.S. citizens (an additional 94 importations occurred among U.S. citizens returning from abroad); and 120 (9.6%) had exemptions under state law. In addition, 54 (4.3%) persons--recruits at Great Lakes Naval Training Station--were considered immune because they had positive results on an indirect immunoperoxidase assay for measles antibody before their illness. Reported by Div of Immunization, Center for Prevention Services, CDC.

Editorial Note

Editorial Note: Although the number of reported measles cases in 1984 has increased from 1983, it is still far lower than the number in the prevaccine era (1950-1962), when an average of more than 525,000 cases was reported annually. Despite the increased occurrence of measles during 1984, its geographic distribution is restricted and focal.

Preventable cases represent a failure to fully implement existing recommendations for measles prevention, and maximal efforts should be directed toward eliminating these cases. By eliminating the preventable cases with current strategies, it should be possible to substantially reduce the number of cases, both preventable and nonpreventable, since the source of many nonpreventable cases is a person with preventable measles.

Although there have been changes in the relative ranking of age groups affected, the actual numbers of cases are small, and it is not possible to draw definitive conclusions about their importance. School-aged children still comprise the majority of preventable cases, and further efforts need to be directed at ensuring that all children covered by state school immunization laws are adequately immunized. Persons who are younger or older represent a more complex problem. Preschoolers who are not in licensed day-care facilities are not reached by existing regulations. Every effort should be made to identify and vaccinate these young children whenever they come in contact with the health-care system. Young adults are perhaps the most susceptible cohort, with estimates of 5%-15% susceptibility in this age group (2). Universities and state health officials need to continue to develop and implement regulations that will ensure immunity for college students and other congregations of young adults (3).

References

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

2. Amler RW, Kim-Farley RJ, Orenstein WA, Doster SW, Bart KJ. Measles on campus. J Am Coll Health 1983;32:53-7.

3. American College Health Association. Statement of immunization policy. November 25, 1983:1-3. *Defined as fever 38.3 C (101 F) or higher, if measured, generalized rash of 3 days duration or longer, and at least one of the following: cough, coryza, and/or conjunctivitis. **A case is considered preventable if measles illness occurs in a U.S. citizen: (1) at least 16 months of age; (2) born after 1956; (3) lacking adequate evidence of immunity to measles (documented receipt of live measles vaccine on or after the first birthday and at least 2 weeks before onset of illness or a physician-diagnosed measles disease or laboratory evidence of immunity); (4) without a medical contraindication to receiving vaccine; and (5) with no religious or philosophical exemption under state law.

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