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Chains of Measles Transmission -- United States, 1982

In 1982, a provisional total of 1,697 cases of measles was reported to CDC, a record low incidence rate of 0.7 cases per 100,000 population for all ages. Fifteen states reported no measles cases all year, and an additional seven states reported only imported cases. Ninety-four percent of the nation's 3,138 counties reported no measles all year.

October 1, 1982, was the target date for eliminating indigenous transmission of measles. To investigate the remaining chains of transmission, CDC has reviewed reporting forms from 556 measles cases, 33% of the 1982 total, submitted by 11 of the 28 states reporting cases. Each form was reviewed for patient age, immunity status, and day-care-center attendance. Cases were grouped using CDC's measles classification system (Table 1) (1). Of 556 persons with measles, 209 (37.6%) were preschoolers (less than 5 years old), and 281 (50.5%) were school-aged (5-19 years old). Overall, 337 (60.6%) cases were not preventable because the patients were either too young or too old for routine vaccination or because they had evidence of immunity. Of the 219 (39.4%) preventable cases, 109 occurred among children who attended schools or day-care centers and were thus readily accessible to control measures. The other 110 were not readily accessible--not school-aged and not known to attend a day-care center.

CDC has also reviewed detailed, written reports of the 14 major outbreaks in 1982. Of 1,697 measles cases, 63% occurred in 14 separate outbreaks or chains of transmission (defined as consisting of two or more generations).* The other 37% occurred sporadically. The 14 outbreaks were reported from nine states and ranged in size from nine to 419 cases in two to 16 generations (Figure 2). Most were of short duration. Sources were identified for 11 of the 14 outbreaks: eight were foreign importations, two were out-of-state importations, and one was indigenous from a child with a medical exemption. In eight outbreaks for which data were available, 42% of subsequent first-generation cases were preventable. At least six of the 14 chains of transmission could have been prevented because the index cases were imported in persons who had not been appropriately vaccinated. In contrast, none of the outbreaks had an indigenous, preventable source. In eight outbreaks for which data were available, the duration of the outbreak was directly related to the proportion of preventable first-generation cases (r=0.95) (Figure 3).

Provisional data for the first quarter of 1983 show a 2-fold increase in measles morbidity over the same period in 1982; however, the chains of transmission have been limited. Approximately 85% of the cases reported have occurred in nine discrete outbreaks, and 53% of the cases reported have occurred among college and university students. Ninety-nine percent of counties reported no measles during the first quarter of 1983. Reported by Div of Immunization, Center for Prevention Services, CDC.

Editorial Note

Editorial Note: Failure to vaccinate--rather than vaccine failure--was the major risk factor for sustained transmission in 1982 (2). Unvaccinated susceptibles were important in sustaining measles transmission. The outbreaks with the greatest proportion of preventable cases in the first generation after the index case continued for the longest period of time, suggesting that the overall immunity levels were lower in areas with high proportions of preventable first-generation cases. The outbreaks were sustained because enough preventable cases, in unvaccinated susceptibles, joined with vaccine failures to increase the total supply of susceptibles.

Although measles in 1983 has affected less than three per 100,000 college students and less than 1% of college campuses, campus outbreaks have focused attention on susceptibility among college students (3). Colleges can help remedy this situation by establishing vaccination requirements for all students born after 1956. In addition, efforts should be made to identify and immunize remaining susceptibles in high schools, especially those in eleventh and twelfth grades.

Indigenous measles has been eliminated from most of the United States. The remaining chains of transmission are limited in size and extent. Analysis of the chains demonstrates that the measles elimination strategy is valid. The major emphasis must now be placed on improving vaccination among preschoolers and college students, while continually enforcing school requirements, and on aggressively responding to the remaining chains of transmission.


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

  2. Amler RW, Bloch AB, Orenstein WA, et al. Measles in the United States: chains of transmission. Proceedings of the 18th Immunization Conference, May 16-19, 1982. Atlanta: CDC (in press).

  3. CDC. Measles outbreaks on university campuses--Indiana, Ohio, Texas. MMWR 1983;32:193-5.

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