Current Trends Measles -- United States, 1989 and First 20 Weeks 1990

MEASLES IN 1989

As of May 11, 1990, local and state health departments reported a provisional total of 17,850* measles cases for 1989--a 423% increase over the 3411 cases reported for 1988 (Figure 1). Forty-one measles-associated deaths have been reported for 1989. Forty-seven states and the District of Columbia reported cases, compared with 36 states that reported cases during 1988. The overall incidence rate in 1989 was 7.3 cases per 100,000 population--more than five times the rate of 1.4 per 100,000 for 1988 (1).

Twenty-three states reported at least 100 cases each. Four states reported greater than 2500 cases each, accounting for 12,127 (67.9%) of the total reported cases: Illinois (3232), Texas (3201), California (3053), and Ohio (2641). Incidence rates of greater than 10.0 per 100,000 population occurred in Illinois (27.8), Ohio (24.3), Texas (19.0), Wisconsin (16.7), Missouri (13.1), and California (10.8).

A total of 16,734 (93.7%) cases met the clinical case definition for measles,** and 4420 (24.8%) were serologically confirmed. Importations from other countries accounted for 321 (1.8%) cases; an additional 222 (1.2%) cases were epidemiologically linked to imported cases.

Children less than 5 years of age accounted for 36.7% of measles cases, compared with 28.7% of cases in 1988 (Table 1). The estimated incidence rates for all age groups were higher in 1989 than in 1988. The largest increases in incidence rates were among adults aged 25-29 years (+600%) and children aged less than 1 year (+592%) and 1-4 years (+562%). The highest incidence rate was among children less than 1 year of age (51.9 per 100,000). Outbreaks

A total of 248 outbreaks, each involving from five to 2440 persons, accounted for 79.4% of the cases. Outbreaks were classified based on the age group with the most cases (2). Fifty-six outbreaks involved predominantly preschool-aged (less than 5 years of age) children, 170 involved predominantly school-aged (5-19 years) persons, and 22 involved predominantly postschool-aged (greater than or equal to 20 years) persons. Outbreaks involving predominantly preschool-aged children accounted for 8007 (44.9%) cases; outbreaks involving predominantly school-aged persons, 5662 (31.7%); and outbreaks involving predominantly postschool-aged persons, 508 (2.8%).

Twenty-five outbreaks involved greater than or equal to 100 cases each and accounted for 60% of the cases reported for 1989; nine were outbreaks involving predominantly preschool-aged children and ranged from 105 to 2440 cases. The largest outbreaks involving predominantly preschool-aged children occurred in Los Angeles (2440 cases), Chicago (2178 cases), and Houston (1434 cases) and accounted for 33.9% of all cases reported for 1989. Sixteen outbreaks involving predominantly school-aged children, ranging from 100 to 437 cases, accounted for 3277 (18.4%) cases. Complications

Complications were reported in 3107 (17.4%) cases, including diarrhea in 1140 (6.4%), otitis media in 1077 (6.0%), pneumonia in 867 (4.9%), and encephalitis in 29 (0.2%). Hospitalization was reported for 2819 (15.8%) persons.

A provisional total of 41 measles-associated deaths were reported, for a case-fatality rate of 2.3 deaths per 1000 reported cases. Deaths were reported from five states (California (17), Illinois (11), Texas (10), and Missouri and Wisconsin (one each)) and the District of Columbia (one), and occurred primarily in outbreaks among preschool-aged children. Twenty-nine (70.7%) deaths occurred among children less than 5 years of age, including nine (22.0%) less than 12 months of age; two deaths were in 11-year-olds. Twenty-nine (93.5%) of these 31 children were unvaccinated. Two children, one of whom had been vaccinated, had serious underlying disease (one case each of leukemia and congenital neurologic defects). The remaining 10 deaths occurred in adults aged 19-33 years. Nine of these patients were unvaccinated. Three had underlying medical conditions (one each with leukemia, scleroderma (not on steroids), and diabetes mellitus). Most deaths were attributed to pneumonia. Vaccination Status

Of reported patients, 7149 (40.1%) were known to have been vaccinated on or after their first birthday (Table 2). Approximately 79% of appropriately vaccinated persons with measles were 5-19 years of age. The remaining 10,654 (59.7%) persons with measles were unvaccinated or inadequately vaccinated (i.e., vaccinated before their first birthday). Of these persons, routine vaccination was indicated for 6073 (57.0% (34.0% of total)). Almost 40% of these vaccine-eligible persons were children 16 months to 4 years of age. Measles occurred in 3699 (20.7%) persons for whom routine vaccination was not indicated; 3203 (17.9% of total) children were less than 16 months of age. Eight hundred eighty-two (4.9%) were unvaccinated for other reasons. MEASLES IN 1990 (FIRST 20 WEEKS)

For the first 20 weeks of 1990 (January 1-May 19), a provisional total of 7653 measles cases was reported, a 39.6% increase over the 5484 cases reported for the same period in 1989 (Figure 2). Cases have been reported from 48 states and the District of Columbia.

Detailed information has been provided on 5180 (67.7%) of the 7653 cases. Of these 5180 patients, 2187 (42.2%) were children less than 5 years of age, including 675 (13.0% of total) less than 12 months of age (Table 1).

Vaccination status was reported for 5178 patients (Table 2). Of these, 1483 (28.6%) were appropriately vaccinated, and 3695 (71.3%) were unvaccinated. Among the unvaccinated patients, routine vaccination was indicated for 1839 (49.8% (35.5% of total)). Routine vaccination was not indicated for 1252 (24.2%) patients. Although most of these were children less than 16 months of age (86.7%), 604 (11.7%) patients were unvaccinated for other reasons (e.g., religious or philosophic exemptions).

At least 88 measles outbreaks are known to be occurring in 25 states. These outbreaks involve preschool-aged children (seven outbreaks); school-aged children (five); college students (10); and other groups (66), such as migrant farm workers and Amish populations. The largest outbreak is occurring in Dallas, where an estimated 2900 confirmed and suspected cases have been reported since December 1, 1989. This outbreak involves primarily unvaccinated preschool-aged children. Outbreaks among preschool-aged children are also continuing in Chicago, Los Angeles, and Milwaukee.

Since January 1, 35 suspected measles-associated deaths have been reported. Most deaths have occurred in unvaccinated preschool-aged children. Reported by: Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The provisional total of 17,850 measles cases reported in 1989 is the largest number reported since 1978. This marked increase in disease incidence has continued through early 1990. The 1990 total is likely an underestimate; reports from high-incidence areas (e.g., Dallas and Los Angeles) indicate that 2-3 times more cases have occurred than have been officially reported through local and state health departments to CDC.

In addition to the increased incidence of measles in all age groups during 1989-1990, the age distribution of cases has changed from that observed in previous years. From 1988 to 1989 the proportion of patients less than 5 years of age increased from 28.6% to 36.7%. For the first 20 weeks of 1990, 42.3% of patients were in this age group. In comparison, a median of 28.5% of patients reported during 1980-1988 were in this age group. Conversely, the proportion of school-aged persons with measles decreased. During 1980-1988, a median of 53.3% of reported cases were in persons 5-19 years of age, compared with 46.4% in 1989; more than half of the patients in this age group were 15-19 years old. In the prevaccine era, greater than 50% of reported measles patients were 5-9 years old; in 1989-1990, this age group represented approximately 10% of total measles cases.

As in 1988, primarily two types of outbreaks occurred in 1989: those among unvaccinated preschool-aged children and those among highly vaccinated ( greater than 90%) school- and college-aged populations. During 1985-1988, most cases were reported from outbreaks involving predominantly school-aged children; a median of 47 outbreaks involving predominantly school-aged children occurred annually, accounting for a median of 51% of all reported measles cases. Also during this period, a median of eight outbreaks involving predominantly preschool-aged children occurred annually, accounting for a median of 20% of reported cases (3). Although the number and size of both types of outbreaks increased in 1989, the relative impact of these outbreaks changed. In 1989, 45% of all cases were reported from outbreaks involving predominantly preschool-aged children, while only 32% occurred in outbreaks involving predominantly school-aged children.

The 41 deaths in 1989 are the largest number reported in one year since 1971, when 90 deaths and 75,290 measles cases were reported. Measles-associated deaths were primarily occurring among unvaccinated preschool-aged children and adults--groups known to be at increased risk for both complications of measles and death (4). Reasons for the apparent increase in the case-fatality rate are unclear but may include the higher proportion of cases occurring among younger age groups; underreporting of less severe cases, particularly in the large outbreaks involving predominantly preschool-aged children; and potential undiagnosed underlying disease in these persons.

The increase in unvaccinated persons with measles reported for 1989 primarily reflected the increasing number of cases reported among unvaccinated inner-city preschool-aged children; to a lesser extent, this trend reflected an increase in cases among children younger than the recommended age for vaccination and among persons with religious or philosophic exemptions to vaccination (5,6). Prevention of outbreaks among preschool-aged children will require intensive efforts to increase age-appropriate vaccination levels in inner-city preschool-aged children and to decrease the age of vaccination to 12 months in some high-risk areas (7).

In addition to the increase in cases among unvaccinated persons, a large number of cases were reported among persons who were appropriately vaccinated. Approximately 2%-5% of persons who receive a single dose of measles vaccine at greater than or equal to 15 months of age will not develop protective immunity (i.e., vaccine failure). If measles virus circulates at relatively low levels, as occurred from 1981 through 1988, then the risk of measles among persons who fail to respond to a single dose of vaccine will be small and these persons will accumulate in the population. Consequently, when measles virus is introduced into environments where large numbers of vaccinated persons congregate (e.g., schools or colleges), the relatively few susceptible persons may be sufficient to sustain transmission and outbreaks may occur. In order to reduce this pool of susceptible persons resulting from vaccine failure, the Immunization Practices Advisory Committee (ACIP) has recommended a second dose of vaccine for groups of persons at high risk for measles, including new entrants to schools and colleges and other institutions for post-high school education (7). If fully implemented, this strategy should eventually eliminate measles outbreaks in these settings. In the meantime, aggressive outbreak control in school-based outbreaks with revaccination of persons at risk will continue to be necessary (7).

References

1. CDC. Measles--United States, 1988. MMWR 1989;38:601-5.

2. Markowitz LE, Preblud SR, Orenstein WA, et al. Patterns of transmission in measles outbreaks in the United States, 1985-1986. N Engl J Med 1989;320:75-81.

3. Gindler J, Atkinson WL, Markowitz LE, et al. The epidemiology of measles in the United States in 1989 (Abstract). In: Proceedings of the Epidemic Intelligence Service 39th Annual Conference. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, 1990:21.

4. Barkin RM. Measles mortality: a retrospective look at the vaccine era. Am J Epidemiol 1975;102:341-9.

5. CDC. Measles--United States, first 26 weeks, 1989. MMWR 1989;38:863-6,871-2.

6. CDC. Update: measles outbreak--Chicago, 1989. MMWR 1990;39:317-9,325-6.

7. ACIP. Measles prevention: recommendations of the Immunization Practices Advisory Committee. MMWR 1989;38(no. S-9). *As of December 31, 1989, a total of 16,236 cases were officially reported to CDC. Through May 11, 1990, CDC's Division of Immunization, Center for Prevention Services, has received reports of 1614 additional cases reported to have occurred in 1989 for a provisional total of 17,850 cases. The final official total may differ slightly. **Fever greater than or equal to 38.3 C (101 F), if measured; generalized rash lasting greater than or equal to 3 days; and at least one of the following: cough, coryza, or conjunctivitis.

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