From February 14 through December 31, 1989, a provisional total of 2232 confirmed cases of measles (1) and eight measles-associated deaths were reported to the Chicago Department of Health (CDH) (Figure 1). The outbreak is continuing, with 389 cases reported from January 1 through May 11, 1990. The 1989 measles incidence rate in Chicago was 74 cases per 100,000 population--10.1 times higher than the overall U.S. incidence rate for 1989 (7.3 per 100,000) (CDC, unpublished data). Four hundred twenty-two (18.9%) cases were serologically confirmed; 1810 (81.1%) were epidemiologically linked to another clinical case of measles.

One thousand six hundred sixty-three (74.5%) patients were less than 5 years of age, including 422 (18.9%) who were less than 1 year of age (Table 1). The highest age-specific attack rates were for infants less than 1 year of age (783 per 100,000) and children 1-4 years of age (697 per 100,000) (Table 1). Blacks accounted for 1594 (71.4%) cases, Hispanics for 506 (22.7%), and whites and other races for 132 (5.9%). Attack rates were highest for blacks (127 cases per 100,000) and Hispanics (92 cases per 100,000) and lowest for whites and other races (11 cases per 100,000).

Five hundred sixty-five (25.3%) persons had been vaccinated on or after their first birthday; 1667 (74.7%) were unvaccinated (Table 2). Vaccine would have been routinely indicated for 929 (55.7% (41.6% of total)) of the unvaccinated patients, of whom 805 (86.7%) were preschool-aged children 1-4 years of age. Measles occurred among 738 (33.1% of total) persons for whom vaccine was not routinely indicated. Of these, 731 (99.1%) were less than 16 months of age, younger than the minimum age for vaccination; 422 (57.2%) were less than 1 year of age.

Seven hundred fifty-five (33.8%) patients required hospitalization. The age-specific hospitalization rate was highest for adults greater than 20 years of age (56/78 (71.8%)) and lowest for persons 5-19 years of age (135/491 (27.5%)). Complications were reported for 579 (25.9%) of all measles patients: 340 (15.2%) had diarrhea; 186 (8.3%), pneumonia; 52 (2.3%), otitis media; and one (0.04%), encephalitis.

Eight measles-associated fatalities were reported, for a case-fatality rate of 3.6 per 1000 reported cases. One death occurred in an unvaccinated 30-year-old man with scleroderma. The remaining seven deaths occurred among unvaccinated children less than 5 years of age; five occurred among children less than 15 months of age.

On May 5, the minimum age for vaccination was lowered citywide to 12 months of age. On July 31, because of the continued high attack rate among infants less than 12 months of age, the minimum age for vaccination was lowered to 6 months in communities with high attack rates. Additional outbreak-control activities from July 31 to September 1 included intensified surveillance; publicity through newspapers, radio, and television; special audits of school vaccination records; establishment of vaccination clinics in two pediatric emergency rooms reporting approximately 45% of cases (2) and in communities reporting the highest attack rates; and door-to-door vaccination by teams sent to housing projects. During these vaccination activities, approximately 27,700 doses of vaccine were administered (40% to children less than 5 years of age)--1.5 times more than the annual average of 18,000 doses of measles vaccine administered by the CDH during the last 5 years.

Because nearly 75% of reported patients were unvaccinated, the CDH reviewed records to estimate the percentage of children entering kindergarten who had been immunized for measles by 2 years of age. The survey included 32 public and 14 parochial schools in 10 communities with high measles incidence rates and eight public or parochial schools in four areas with low incidence rates. In 32 public schools for which student racial characteristics were available, enrollment was classified as predominantly white, black, or Hispanic. An average of 80% of students in schools with predominantly white enrollment had received measles vaccine by 2 years of age, compared with an average of 50% and 52% of students in schools with predominantly Hispanic and black enrollment, respectively. An average of 27% and 29% of students in schools with predominantly black and Hispanic enrollment, respectively, first received measles vaccine the year of school entry (at 4-5 years of age), compared with 7% of students in schools with predominantly white enrollment (Figure 2, page 325).

Measles vaccination levels among 2-year-old children in areas with high measles attack rates averaged 49% (range: 45%-55%), compared with average levels of 79% (range: 75%-85%) in areas with low attack rates. The proportion of children who were appropriately vaccinated by 2 years of age (i.e., four doses of diphtheria and tetanus toxoids and pertussis vaccine, three doses of oral poliovirus vaccine, and one dose of measles-mumps-rubella vaccine) in areas with high measles incidence was 26%, compared with 50% in areas with low incidence. In contrast, the average measles vaccination level for children enrolled in kindergarten and first grade in the 1988-89 school year was 95%. Reported by: RM Krieg, PhD, RW Biek, MD, CR Catania, JW Masterson, MPH, Chicago Dept of Health; R March, Immunization Program, RJ Martin, DVM, Div of Infectious Diseases, Illinois Dept of Public Health. Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Measles outbreaks in inner cities continue to occur primarily among unvaccinated black and Hispanic preschool-aged children (2-5). In 1989, three large preschool outbreaks in Chicago, Houston, and Los Angeles accounted for 35% of all reported cases in the United States (CDC, unpublished data). These outbreaks reflect the failure of current strategies to achieve high vaccination coverage levels among preschool-aged children.

Although most children are well vaccinated by school entry, measles vaccination levels in Chicago were as low as 49% among 2-year-old children. In addition, age-appropriate vaccination levels for all antigens were as low as 25%. Although these data reflect vaccination levels 3 years ago, communities with the lowest coverage reported the highest measles attack rates in the outbreak. Conversely, districts with 75% or higher coverage reported low disease incidence. Other cities with measles outbreaks among preschool-aged children have also found measles vaccination levels as low as 49% in 2-year-old children and low age-appropriate coverage for all antigens (4-6). Outbreaks among urban preschool-aged children with poor age-appropriate coverage for all antigens reflect the difficulty in reaching this population, which often has limited contact with the health-care system. Efforts must be intensified to increase the availability of vaccination services and to ensure that all eligible children are vaccinated whenever they present for health care. Specific approaches could include extending the hours of public health clinics to accommodate working families; expanding services to include walk-in vaccination clinics at all facilities on a daily basis; integrating vaccination services into existing programs that serve inner-city preschool-aged children (e.g., Women, Infants and Children and Aid to Families with Dependent Children); targeting health education at low socio economic parents; and educating medical personnel to use all health-care contacts as opportunities to vaccinate susceptible children.

In this outbreak, 565 (25.3%) measles patients with known vaccination status had been vaccinated on or after their first birthday. To reduce the number of measles cases attributed to primary measles vaccine failure, which accounted for almost 40% of cases in 1989 (CDC, unpublished data), the Immunization Practices Advisory Committee (ACIP) has recommended a two-dose schedule for measles vaccination (7). However, the highest priority remains that all susceptible persons receive at least one dose of vaccine at the recommended age. If coverage with at least one dose of vaccine is not increased among inner-city preschool-aged children, additional outbreaks of measles and other vaccine-preventable diseases can be expected.

References

1. CDC. Classification of measles cases and categorization of measles elimination programs. MMWR 1983;31:707-11.

2. CDC. Measles outbreak--Chicago, 1989. MMWR 1989;38:591-2.

3. CDC. Measles--Los Angeles County, California, 1988. MMWR 1989;38:49-52,57.

4. CDC. Measles--Dade County, Florida. MMWR 1987;36:45-8.

5. CDC. Measles--New Jersey. MMWR 1986;35:213-5.

6. Hutchins SS, Escolan J, Markowitz LE, et al. Measles outbreak among unvaccinated preschool-aged children: opportunities missed by health care providers to administer measles vaccine. Pediatrics 1989;83:369-74.

7. CDC. Measles prevention: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1989;38(no. S-9).

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