Measles -- United States, First 26 Weeks, 1989

During the first 26 weeks of 1989, local and state health departments reported a provisional total of 7335 measles cases to CDC--a 380% increase over the 1529 cases reported for the same period in 1988; at least 10 measles-associated deaths were also reported. In addition, another 30 suspected measles-associated fatalities are being investigated by local and state health departments and CDC. Forty states and the District of Columbia reported cases, compared with 36 states for the first 26 weeks of 1988. During the 1989 period, the incidence rate was 3.0 cases per 100,000 population--five times the rate of 0.6 per 100,000 for the same period in 1988 and more than double the rate for all of 1988 (1.4 per 100,000) (1).

Thirteen states reported at least 100 cases and accounted for 6588 (89.8%) of all reported cases: Texas (2764), California (1189), Ohio (661), Illinois (489), New Jersey (271), Missouri (237), New York (193), North Carolina (167), Pennsylvania (147), Connecticut (146), Nebraska (110), Kansas (108), and Oklahoma (106). Incidence rates of greater than 4.0 per 100,000 population occurred in Texas (16.4), Delaware (8.9), Nebraska (6.9), Ohio (6.1), Missouri (4.6), Connecticut (4.5), Kansas (4.3), Illinois (4.2), California (4.2), and Rhode Island (4.1).

For 6880 (94%) cases, more detailed information was collected by CDC. Of these, 6373 (92.6%) met the clinical case definition for measles,* and 1775 (25.8%) were serologically confirmed.

Consistent with the usual seasonal pattern, most of the 6880 cases occurred from March through May (weeks 9-19). Ninety-three (1.4%) cases were imported from other countries; an additional 157 (2.3%) cases were epidemiologically linked to imported cases.

One hundred twenty-eight outbreaks involving five or more persons were reported and accounted for 78.8% of the 6880 cases. Almost half the cases occurred in outbreaks involving greater than or equal to 100 persons. The three largest outbreaks occurred in Houston, Los Angeles, and Chicago and accounted for 31.9% of the 6880 cases. Twenty percent of all cases were reported from the outbreak in Houston.

Detailed information on age was provided for 6873 (99.9%) cases (Table 1). Children less than 5 years of age accounted for 30.2% of measles cases, compared with 19.4% during the same period in 1988. Of this group, 664 (32.0%) were less than 1 year of age. School-aged children (5-19-year-olds) accounted for 51.1% of cases in 1989 but for 66.2% of cases in 1988. The incidence rates for all age groups were higher in 1989 than in 1988; the highest were for 0-4-year-olds (11.3 per 100,000) and 15-19-year-olds (11.2 per 100,000).

Complications were reported in 672 (9.8%) cases, including otitis media in 318 (4.6%) cases, pneumonia in 178 (2.6%), diarrhea in 171 (2.5%), and encephalitis in five (0.1%). Nine hundred thirteen patients (13.3%) were hospitalized, and 10 measles-associated fatalities were reported (case-fatality rate: 1.5 deaths per 1000 reported cases). Eight of the deaths were reported in children less than 5 years of age, all of whom were unvaccinated. None had a reported underlying illness or immunodeficiency. Most deaths have been attributed to pneumonia.

The setting of transmission was reported for 4057 (59.0%) cases: 1899 (46.8%) persons acquired measles in primary or secondary schools; 796 (19.6%) in colleges or universities; 627 (15.5%) at home; 248 (6.1%) in medical settings; 89 (2.2%) in day-care centers; and 398 (9.8%) in other settings, including work, church, and the military. The number of cases occurring in colleges and universities was 60.7% higher than those from the same period in 1988.

A total of 3520 (51.2%) measles patients had been vaccinated on or after their first birthday, including 1298 (18.9%) who had been vaccinated between the ages of 12 and 14 months; 3340 (48.5%) were unvaccinated or vaccinated before their first birthday. Of the 6873 patients for whom age information was provided, 3512 (51.1%) were school-aged children, 2830 (80.6%) of whom had been appropriately vaccinated. As in 1988, most vaccine failures occurred in 12-19-year-olds (Figure 1), and children less than 2 years old were most affected. Measles occurred in 1261 (18.3%) persons for whom vaccine was not routinely indicated, and 226 (3.3%) were unvaccinated for other reasons. Of those unvaccinated, vaccine would have been routinely indicated for 1853 (55.5% (26.9% of total)) (Table 2). The percentage of cases in unvaccinated persons for whom vaccination was indicated varied by age group. Most occurred among children 16 months to 4 years of age (64.7%) and among persons greater than or equal to 20 years of age (52.9%). Reported by: Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: In 1989, measles outbreaks have involved previously vaccinated school-aged children and college students, as well as unvaccinated urban preschoolers who are predominantly black and Hispanic (2). Large outbreaks involving minority populations are continuing in Houston, Los Angeles, and Chicago. Aggressive outbreak-control strategies aimed toward reaching inner-city children have been implemented and include intensified surveillance, door-to-door vaccination in high-risk communities, emergency department vaccination clinics, and lowering of the recommended age for vaccination to 6 months during outbreaks, with revaccination at 15 months.

The increased incidence of measles in preschoolers living in densely populated urban areas reflects low vaccination levels in these populations. While these children are generally well immunized by the time they enter school, immunization levels in some inner cities are as low as 49% in children 2 years of age (3). Many of these children receive intermittent health care and are less likely to be age-appropriately immunized with other antigens (4). Innovative efforts need to be directed toward reducing barriers to immunization services and toward full use of existing opportunities to vaccinate eligible children whenever they present for health care. This approach should increase opportunities for vaccine administration in highly susceptible populations and reduce transmission to infants too young for routine immunization.

Suboptimal vaccination also played a major role in measles incidence among adults: 53% of cases in adults greater than or equal to 20 years of age were in unvaccinated persons for whom vaccine was indicated. Many young adults may have missed immunization during the first years after vaccine licensure, may not have been immunized before the adoption of comprehensive state school laws, or may not have been infected naturally because of declining measles transmission.

In 1989, the number of measles-associated deaths and the case-fatality rate are higher than in any year since 1971 (CDC, unpublished data). The reason for this increase is not known but could be associated with underreporting of cases, resulting in spuriously high case-fatality rates.

More than half of measles cases occurred among appropriately vaccinated children 5-19 years of age. Primary vaccine failure (rather than waning of vaccine-induced immunity) may be the major reason for the occurrence of measles in this group (5). To reduce the number of primary vaccine failure-related cases, the Immunization Practices Advisory Committee (ACIP) has recommended a routine two-dose measles vaccine schedule (6). The initial dose is to be administered to children at 15 months of age, except for children in high-risk areas for preschool transmission, who should be vaccinated at 12 months of age. The second dose is recommended at school entry (4-6 years of age), although localities can choose other ages, such as entry to middle school or junior high school. Both doses should generally be given as measles-mumps-rubella vaccine. In addition, ACIP recommends that colleges and other educational institutions require documentation of two doses of live measles vaccine or other evidence of measles immunity (i.e., prior physician diagnosis or laboratory evidence) for entering students born in or after 1957.

Two approaches to measles control and prevention are crucial until all localities can fully implement a two-dose schedule. The highest priority should always be given to assuring that susceptible persons receive at least one dose of vaccine. In addition, during an outbreak, localities should implement the new outbreak-control recommendations (6), which call for vaccination of all persons at risk (e.g., students attending schools where cases have occurred) who have not received two prior doses and have no other evidence of measles immunity. The ultimate goal, however, will be to implement a routine two-dose schedule in all communities.

References

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

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

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

4. 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.

5. Markowitz LE, Preblud SR, Fine PEM, Orenstein, WA. Duration of live measles vaccine-induced immunity. Pediatr Infect Dis J (in press).

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

*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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