Current Trends Measles --- United States, 1990

As of May 10, 1991, local and state health departments reported a provisional total of 27,672* measles cases in the United States for 1990---a 52.1% increase over the 18,193 cases reported for 1989 (1) (Figure 1)---and 89 suspected measles-associated deaths. Cases were reported from 49 states and the District of Columbia. The overall incidence rate in 1990 was 11.1 cases per 100,000 population. This report summarizes epidemiologic features of measles cases reported for 1990 and compares findings with cases reported for 1989. Characteristics

In 1990, children less than 5 years of age accounted for 48.1% of measles cases, compared with 36.6% of cases in 1989 (Table 1). Persons greater than or equal to 20 years of age accounted for 22.5% of all reported cases in 1990, compared with 17.0% in 1989.

Estimated incidence rates were higher in 1990 than in 1989 for all age groups, except 15- to 19-year-olds. The largest increases in incidence rates were among children less than 1 year of age (137.6%) and adults greater than or equal to 25 years of age (130.0%). The highest incidence rates were among children aged less than 1 year (119.3 per 100,000) and 1--4 years (58.3 per 100,000).

Information on race/ethnicity was available for 11,083 (40.1%) cases reported from 34 states and the District of Columbia (no race/ethnicity information was available for cases reported from the other 15 states, including California). Of these, 6192 (55.9%) occurred among non-Hispanic whites; 2472 (22.3%), non-Hispanic blacks; 2082 (18.8%), Hispanics; and 337 (3.0%), other racial or ethnic groups. Incidence rates were highest for Hispanics (29.5 cases per 100,000 population) and blacks (12.3 per 100,000) and lowest for non-Hispanic whites (5.2 per 100,000).

Importations from other countries accounted for 377 (1.4%) cases; an additional 188 (0.7%) cases were epidemiologically linked within two generations of transmission to imported cases. Of the 377 cases, 249 (66.0%) were acquired in Mexico, and 95 (25.2%) in other Central American, South American, or Caribbean countries. Outbreaks

A total of 240 outbreaks, involving from five to 7514 persons, accounted for 87.0% of the cases. Outbreaks affecting predominantly preschool-aged children involved 19,827 (71.7%) cases; school-aged persons, 2842 (10.3%) cases; and postschool-aged persons, 1376 (5.0%) cases. The largest outbreaks involved predominantly preschool-aged children and occurred in Los Angeles (7514 cases); Dallas (2331); New York City (1108); San Diego (1049); and Bakersfield/Kern County, California (1011). These outbreaks accounted for 47.0% of all cases reported for 1990. Vaccination Status

Vaccination status was known for 27,632 (99.9%) patients. Of these, 5100 (18.4%) were known to have been vaccinated on or after their first birthday (Table 2); approximately 71.4% of these persons were 5--19 years of age. Of the 22,532 (81.4%) persons who were unvaccinated or inadequately vaccinated (i.e., vaccinated before their first birthday), routine vaccination was indicated for 12,268 (54.4% (44.3% of total**)). Almost 40% of these vaccine-eligible persons were children 16 months to 4 years of age. Measles occurred in 8698 (31.4% of total) persons for whom routine vaccination was not indicated, of whom 7257 (83.4%) were children less than 16 months of age. Of the 1566 persons (5.7% of total) who were unvaccinated for other reasons, 1424 (90.9%) were persons with religious or philosophic exemption to vaccination. Complications of Measles

Complications were reported in 6274 (22.7%) cases, including diarrhea in 2606 (9.4%), otitis media in 1829 (6.6%), pneumonia in 1803 (6.5%), and encephalitis in 36 (0.1%). Hospitalization was reported for 5844 (21.1%) persons. Deaths

A provisional total of 89 measles-associated deaths were reported, for a death-to-case ratio of 3.2 deaths per 1000 reported cases. Deaths were reported from 15 states. Forty-nine (55.1%) deaths occurred among children less than 5 years of age, including 15 (16.9%) children less than 12 months of age and 13 (14.6%) children 5--19 years of age. The other 27 (30.3%) deaths occurred among adults greater than or equal to 20 years of age. Eighty-one (91.0%) suspected measles-associated deaths occurred among unvaccinated persons. Reported by: Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The provisional total of 27,672 measles cases reported in 1990 is the largest number reported since 1977. Cases were reported from every state except North Dakota; however, 61% of all cases were reported by two states, California (12,479 cases) and Texas (4403 cases).

In addition to increases in the United States, increases in the occurrence of measles during 1989--1990 were reported by many other countries of the Western Hemisphere, including Canada, El Salvador, Guatemala, Honduras, Jamaica, Mexico, and Nicaragua. Although the cause of this hemispherewide trend in measles activity is unknown, it has increased the likelihood that measles will be imported into and exported from the United States.

The change in age distribution of measles patients noted in 1989 (3) continued in 1990. For the first time since detailed information on the ages of reported patients became available in 1973, the proportion of cases among children less than 5 years of age in 1990 exceeded the proportion among school-aged children.

The 89 deaths in 1990 are the largest number reported in a single year since 1971 (90 deaths and 75,290 reported cases) and the highest death-to-case ratio documented in the past 30 years. Although the reasons for these increases have not yet been defined, probable contributing factors include underreporting of less severe cases (particularly from areas experiencing large outbreaks) and the shift of the predominant age of reported cases to children less than 5 years and persons greater than or equal to 20 years (groups at higher risk for complications) (4).

Failure to vaccinate children at the appropriate age was the major factor contributing to the resurgence of measles in the United States in 1989--1990 (National Vaccine Advisory Committee, unpublished data, 1991). Surveys in areas experiencing measles outbreaks indicate that as few as 50% of children have been vaccinated against measles by their second birthday (5), and that black and Hispanic children are less likely to be age-appropriately vaccinated than are white children (6).

Prevention of measles outbreaks among preschool-aged children will require intensive efforts to increase age-appropriate vaccination levels among inner-city preschool-aged children. Strategies that should improve immunization levels include: 1) reducing barriers to vaccination (e.g., increasing the number of clinic hours when vaccines are given and the availability of walk-in vaccination services); 2) taking advantage of all opportunities to vaccinate (e.g., simultaneous use of multiple vaccines whenever possible, and excluding from vaccination only persons with valid contraindications); 3) using innovative vaccine delivery techniques, such as vaccination in hospital emergency departments; and 4) increasing the number of children who return for vaccination at the appropriate age by improving follow-up and recall systems. CDC is supporting demonstration projects to examine the feasibility of assessing immunization status and facilitating vaccination of children participating in entitlement programs (e.g., Women, Infants, and Children program and Aid to Families with Dependent Children).

References

1. CDC. Summary of notifiable diseases, United States, 1989. MMWR 1989;38(54).

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

3. CDC. Measles---United States, 1989, and first 20 weeks 1990. MMWR 1990;39:353--5,361--3.

4. Atkinson WL, Markowitz LE. Measles and measles vaccine. Seminars in Pediatric Infectious Diseases 1991;2:100--7.

5. CDC. Measles vaccination levels among selected groups of preschool-aged children---United States. MMWR 1991;40:36--9.

6. CDC. Update: measles outbreak---Chicago, 1989. MMWR 1990;39:317--9,325--6. *As of December 31, 1990, a total of 26,520 cases had been officially reported to CDC. Through May 10, 1991, CDC's Division of Immunization, Center for Prevention Services, had received reports of 1152 additional cases reported to have occurred in 1990, for a provisional total of 27,672 cases. The final total may differ slightly.

**Unvaccinated persons greater than or equal to 16 months of age without medical contraindications or religious exemption to vaccination. This represents a minimal estimate, because the Immunization Practices Advisory Committee (ACIP) recommends that the routine age for the first dose of measles vaccine be lowered from 15 months to 12 months in areas with high risk for measles among preschool-aged children (2).

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