During the first 26 weeks of 1984, a provisional total of 1,759 measles cases was reported in the United States (incidence rate 0.8 per 100,000 population) (Figure 1). This represents a 60.6% increase from the 1,095 cases reported during the same period in 1983 (0.5/100,000). A total of 1,234 cases (70.2%) was reported from four states--Michigan (430), Texas (377), California (267), and Illinois (160). Nine states (New Mexico, Michigan, Hawaii, New Hampshire, Texas, Washington, Utah, Illinois, California) and New York City had incidence rates of 1/100,000 population or higher.

Although the overall incidence rate increased, the number of states reporting measles decreased during the first 26 weeks of 1984, compared with the same period of 1983. Twenty-four states reported no measles cases (indigenous or imported), compared with 22 states and the District of Columbia during the same period in 1983. In 1984, 80 (2.5%) of the nation's 3,139 counties reported measles cases during the first 26 weeks, compared with 95 (3.0%) during the same period in 1983 (Table 1).

One hundred seventy-five cases (9.9%) were associated with international or out-of-state importations--an average of 6.7 cases per week--compared with 174 cases during the same period in 1983 (1).

During the first 26 weeks, detailed information was provided to the Division of Immunization, CDC, on 1,765 cases. The difference between this number and the 1,759 cases reported to the MMWR reflect delays in reporting. Of 1,765 cases, 1,723 (97.6%) met the standard clinical case definition for measles,* and 721 (40.8%) were serologically confirmed.

Among most of the measles patients, onset of rash occurred from week 9 through week 15, peaking at week 11 (130 cases) (Figure 2).

Age characteristics of reported cases changed from 1983 to 1984 (Table 2). In 1983, the highest incidence rates were reported for preschoolers. In contrast, the rates for the first 26 weeks of 1984 were greatest for children 10 years to 14 years of age who experienced a more than twofold increase in incidence rates, compared with all of 1983. Of the 351 preschoolers who had measles in 1984, 92 (26.2%) were under 12 months of age; 68 (19.4%) were 12-14 months of age; 18 (5.1%) were 15 months; and 173 (49.3%) were 16 months to 4 years of age. Persons 12-14 months of age accounted for 3.9% of the 1,765 cases.

Of the 1,765 persons with measles, 911 (51.6%) had been vaccinated; 776 (44.0%) had been vaccinated on or after the first birthday; and 135 (7.6%) had been vaccinated before the first birthday (Table 3). A total of 854 (48.4%) persons were either unvaccinated or of unknown vaccination status. Prior physician-diagnosed measles in the absence of vaccination was reported for 21 (1.2%) persons.

Of the 1,765 cases, 610 (34.6%) were classified as preventable** (1) (Table 4). The highest proportion of preventable cases occurred among persons who were not of school age. More than 70% of the cases among children 16 months to 4 years and adults 20-24 years were preventable. Although more than half of the preventable cases occurred among persons 5-19 years of age, only 29.5% 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 1,155 persons who had nonpreventable measles, 178 (15.4%) were too young for routine vaccination (15 months of age or under). Fifty-seven (4.9%) were born before 1957; vaccination is not ordinarily recommended for this group. Of the 920 persons 16 months to 27 years of age who acquired measles, 775 (84.2%) had been vaccinated on or after the first birthday; 18 (2.0%) had prior physician-diagnosed measles; 32 (3.5%) had international importations and were not U.S. citizens; and 41 (4.5%) had exemptions under state law. In addition, 54 (5.9%) persons--recruits at Great Lakes Naval Training Station--were considered immune because they had positive results to an indirect immunoperoxidase assay for measles antibody before their illnesses (Table 5). Reported by N El-Tantawy, MD, Emory University School of Medicine, Atlanta, Georgia; Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Although the number of reported measles cases has increased in 1984, compared with the same period in 1983, it is still far below the number in the prevaccine era (1950-1962), when an average of over 525,000 cases was reported annually. Despite the increased occurrence of measles during the first 26 weeks of 1984 over all of 1983, the geographic distribution of measles is more restricted and focal.

A total of 43.9% of the persons who had measles in 1984 had been adequately vaccinated. This is within expected limits, given the high vaccine coverage in the United States (2). Since 1980, over 95% of kindergarten and first-grade students have had evidence of measles immunity. Higher coverage will be associated with higher proportions of persons who are vaccinated. Recent epidemiologic evaluations have shown a measles vaccine efficacy of 90% or higher. The increased occurrence of measles in 1984 does not appear to be due to poor vaccine efficacy.

Greater emphasis needs to be placed on ensuring that persons 10-14 years old and 15-19 years old have evidence of measles immunity (3). Enactment and vigorous enforcement of regulations requiring all students in grades kindergarten through 12 to have evidence of immunity is an important means of ensuring high levels of measles immunity (2).

Further efforts need to be made in preschool- and post-school-aged groups. Over 70% of the cases among young adults (20-24 years old) and preschoolers (16 months to 4 years old) were preventable. Every opportunity should be taken to vaccinate susceptible children against measles. Many colleges are considering regulations requiring evidence of measles immunity for matriculation (4). All institutions where young adults congregate should consider requiring evidence of measles immunity.

References

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

2. CDC. Measles Surveillance Report No. 11, 1977-1981. September 1982.

3. ACIP. Measles prevention. MMWR 1982;31:217-24, 229-31.

4. American College Health Association. Statement of immunization policy. November 25, 1983;1-3. *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. **A case is considered preventable if measles 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 or laboratory evidence of immunity), (4) without a medical contraindication to receiving vaccine, and (5) with no religious or philosophic exemption under state law.

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