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Measles -- Arizona
From March 14, to July 11, 1985, 54 cases of measles were reported from Maricopa County, Arizona (Phoenix and surrounding area), to the Arizona Department of Health Services. Twenty-five (46.3%) cases were serologically confirmed.
The outbreak, which spread from a large school-based outbreak in neighboring Pima County (Tucson and surrounding area) began February 19. Two separate introductions of measles into Maricopa County apparently occurred. The first patient, a 25-year-old elementary school teacher, had onset of rash March 11 (Figure 1). The source of her infection was a Pima County student to whom she had been exposed while on a bus trip to a religious event. There was no known spread of measles from this patient. The second introduction of measles into Maricopa County involved five patients with rash onset from April 8 to April 15. Three of these patients acquired measles from a Pima County student at a swim meet in Maricopa County; one patient was in Tucson during all her probable exposure period; and the fifth had no known source.
Sixteen (29.6%) of the 54 patients were Hispanic, and 38 (70.4%) were white non-Hispanic. Sixteen (29.6%) patients were under 16 months of age; 27 (50.0%) were preschool-aged (0-4 years old); and 19 (35.2%) were school-aged (5-19 years old).
The overall attack rate in Maricopa County was 3.6 cases per 100,000 population. The highest reported attack rates were in the southwestern and western portions of the county, which are generally rural and where residents are of lower socioeconomic status. The highest attack rate occurred in the Buckeye community (378.6 cases/100,000 population), which is approximately 20 miles southwest of Phoenix. Race-specific attack rates were 8.0 cases/100,000 Hispanics and 3.1 cases/100,000 white non-Hispanics. Age-specific attack rates were calculated for the age groups for which county population data were available and ranged from a high of 22.2/100,000 children 0-5 years of age to 2.9/100,000 persons 20-29 years of age.
Sixteen (29.6%) patients had diarrhea; five (9.3%) developed otitis media; and two (3.7%) acquired pneumonia. One patient, a 19-year-old pregnant female, developed premature onset of labor and delivered an infant at 32 weeks' gestation. Eight (14.8%) patients were hospitalized. There were no measles-associated fatalities.
The probable setting or source of transmission was known for 34 (63.0%) of the patients: household/family contact--20 (58.8%); neighborhood--six (17.6%); school/school-related activity--six (17.6%); and medical facility--two (5.9%). Of 17 preschool-aged patients for whom sources were known, six (35.3%) acquired disease from another preschool-aged individual.
Twenty-nine (53.7%) cases were considered preventable, according to the CDC classification.* Of the 25 patients with nonpreventable measles, 13 (52.0%) had histories of appropriate vaccination; 10 (40.0%) were under 16 months of age; and two (8.0%) were born before 1957. All 17 patients from 16 months through 4 years of age were unvaccinated (i.e., preventable cases). Measles was preventable in five (41.7%) of the 12 school-aged patients.
Outbreak-control activities included intensified surveillance through publicity in the local press, improved case investigation, special vaccination clinics at various locations throughout the county, and exclusion of students who did not have adequate evidence of measles immunity in their school health records. Based on the schools' assessments of student immunization records, 7,098 (2.5%) of the 288,919 students enrolled in the county were excluded from school on May 8. By May 13, 6,280 (88.5%) of the 7,098 excluded students had provided documentation of measles immunity and were allowed to return to school.
To assess the accuracy of school immunization records, state and local health officials reviewed every tenth record in each of 48 schools in the county (20 high schools and 28 elementary schools) during the first week of exclusion. These schools had an overall enrollment of approximately 55,500. Of 5,302 records reviewed that had been reported to contain adequate evidence of measles immunity, 419 (7.9%) were inadequate according to the criteria of the Immunization Practices Advisory Committee.** To be considered complete, dates of measles vaccination needed to include at least the month and year of vaccination. The inadequacy rates were 2.2% (45/2,041) in elementary school records and 11.5% (374/3,261) in high school records. School-specific inadequate-record rates ranged from 0.0% to 9.5% in elementary schools (median 0.6%) and from 0.0% to 27.3% in high schools (median 8.2%). In 14 elementary schools and one high school, all records audited were found to be adequate. Reported by J Swanson, D Campos-Outcalt, MD, R Harmon, MD, Maricopa County Div of Public Health, B Olson, SJ Englender, MD, LF Novick, MD, GG Caldwell, MD, State Epidemiologist, Arizona Dept of Health Svcs; Div of Field Svcs, Epidemiology Program Office, Div of Immunization, Center for Prevention Svcs, CDC.
Editorial Note: In 1985, 241 measles cases were provisionally reported in Arizona, including 234 indigenous cases and seven out-of-state or international importations. Over 90% of these 241 cases occurred in the Pima County and Maricopa County outbreaks. The 241 Arizona cases represent 8.9% of the provisional total of 2,704 cases reported in the United States. The only states reporting more cases in 1985 were Texas (409 cases), Illinois (303), and California (269). In contrast to 1985, a total of only 26 cases was reported from Arizona during the 4-year period 1981-1984.
The three major components of the current measles elimination strategy are: (1) high immunization levels; (2) effective surveillance; and (3) aggressive outbreak control. The Maricopa County outbreak illustrates two important aspects of achieving and maintaining high immunization levels: age-appropriate vaccination and school immunization laws. Fifty percent of the cases in the Maricopa County outbreak occurred among preschool-aged children. By contrast, preschool-aged children accounted for 25.9% of all reported cases in the United States in the first 26 weeks of 1985 (1). This and other outbreaks (2-5) suggest that preschool-aged children can contribute substantially to ongoing transmission. The high proportion of preschool-aged children who were unvaccinated emphasizes the need to vaccinate children promptly at 15 months of age.
Fifty-four percent of cases in this outbreak were preventable. According to preliminary data for 1985, approximately 29% of all reported cases in the United States were preventable. The higher proportion of preventable cases in Maricopa County is primarily due to the fact that measles was preventable in all the preschool-aged patients above the recommended age for vaccination.
Reported school vaccination levels for Maricopa and Pima Counties were 97.2% and 95.5%, respectively. A review of school immunization records in Maricopa County revealed a relatively high proportion considered to be inadequate. Other studies have shown that inability to obtain provider verification of school immunization data is a risk factor for developing measles (6-7). These studies provide additional evidence that school immunization records may be inaccurate in some areas. The accuracy of school immunization records probably varies depending on the degree of enforcement of school immunization requirements.
Elementary school immunization records in Maricopa County were more accurate than high school records. Immunization records for high school and college students may be less accurate than those for younger students because of the greater time lapse since vaccination and because many of the older students may have enrolled in school before the vigorous enforcement of school immunization laws.
All 50 states and the District of Columbia have school immunization requirements for measles. As of September 1985, they applied to grades K-12 in 44 states (including Arizona) and the District of Columbia, grades K-5 in Idaho, and new entrants in the remaining four states (8). The Maricopa County outbreak illustrates the need for vigorous enforcement of these requirements to maintain accurate immunization records and high immunization levels in schools. Since the majority of preventable measles cases occurs among school-aged individuals (1), stronger enforcement of school immunization requirements will hasten the elimination of indigenous measles in the United States.
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