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Measles -- United States, 1983

In 1983, the reported occurrence of measles reached its lowest level since national reporting of measles began in 1912. A provisional total of 1,436 cases was reported, for a record low incidence rate of 0.6 cases per 100,000 population for all ages (Figure 1). This is a 99.7% reduction from the prevaccine era, when, from 1950 to 1962, an annual average of 525,730 cases was reported (315.2 cases/100,000 population), and a 16.2% reduction from the 1,714 cases reported in 1982, the previous year of record low incidence (0.7/100,000) (1). Fewer than 100 indigenous cases* were reported each week in 1983, except week 12, when 138 such cases were reported. Fewer than 50 such cases were reported during 45 weeks, and fewer than 10 were reported during 22 weeks.

Of 1,136 indigenous cases, 877 (77.2%) were reported from four states--Indiana (402), Illinois (173), California (153), and Florida (149). Most other areas reported few or no measles cases (Figure 2). Twenty-six states and the District of Columbia reported no indigenous cases all year, compared to 22 states in 1982. Of the remaining 24 states, 20 states and New York City reported fewer than 50 indigenous cases, and 15 states reported fewer than 10 such cases. Of the nation's 3,139 counties, 3,002 (95.6%) reported no measles cases during the entire year, compared to 2,944 (93.8%) in 1982. Every county was free of reported measles for at least 6 consecutive weeks in 1983. Only six counties (0.2%) reported measles during the last 4 weeks of 1983. The three chains of transmission that occurred during the last 2 months of the year were concentrated in certain subpopulations that either refused immunization for religious or philosophic reasons or did not routinely seek medical care or immunization (3).

Most transmission in 1983 was concentrated in settings other than primary or secondary schools. Of 31 discrete chains of transmission** involving 1,233 cases, five chains accounted for 62.7% (900/1,436) of all cases reported in 1983. All five occurred primarily in settings other than primary or secondary schools. The largest chain, which accounted for 32.4% (465/1,436) of all cases in 1983, was concentrated among college students (4). Three additional chains (362 cases) occurred primarily among children less than 5 years old (5). The fifth chain (73 cases) involved schoolchildren and other age groups, but most transmission occurred when schools were not in session. Eleven of the 26 smaller chains of transmission were concentrated in groups other than schoolchildren. The remaining 15 smaller chains (209 cases) principally or partially involved schoolchildren. Of these, 10 chains (90 cases) lasted two to three generations, and five chains (119 cases) lasted four to seven generations. Thus, chains of transmission in primary and secondary schools accounted for only 14.6% (209/1,436) of reported cases in 1983.

According to detailed information received by CDC's Division of Immunization, international importations and associated cases together accounted for 14.7% (211/1,436) of all measles cases reported in 1983. Ninety (6.3%) cases were international importations,* with sources from 30 different countries--an average of 1.7 international importations per week. In addition, 121 cases were epidemiologically linked to 26 international importations within two generations of infection. Reported by Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The target date for measles elimination was October 1, 1982. Although elimination has not yet been achieved, these provisional data demonstrate substantial changes in the epidemiology of measles in the United States in 1983. The lack of measles transmission in over 95% of counties and the lack of reported incidence in every county for 6 or more weeks indicate that transmission was at least temporarily interrupted in every community in the United States during 1983. The data also suggest that less than 15% of documented measles transmission in 1983 involved primary and secondary schools, reflecting the dramatic success of state school immunization requirements in raising measles immunization levels and lowering measles incidence rates in schoolchildren. In the 1982-1983 school year, immunity to measles was documented*** for 97% of children in the United States entering school for the first time.

Nevertheless, several important challenges to elimination remain. Four of the five largest outbreaks occurred primarily among preschoolers under 5 years old and college students who are not directly affected by state immunization requirements. Outbreaks among preschoolers were not concentrated in licensed day-care centers, where immunization requirements have been implemented by 45 states and the District of Columbia. Outbreaks among college and university students indicate that sufficient numbers of susceptibles may exist to sustain transmission when measles is introduced. Many may have missed needed vaccinations or may have escaped natural infection because of decreasing transmission during their childhood. Outbreaks on campuses were difficult to control because susceptible students could not be identified readily. Few campuses required or systematically recorded documentation of immunity. In the future, measles cases among young adults may be difficult to identify because physicians who commonly treat this group may not consider measles as a likely diagnosis (6).

The exact date of the elimination of indigenous measles transmission from the United States will only be known in retrospect (7). The available data demonstrate that the measles elimination strategy--achievement and maintenance of high immunization levels, development of strong and effective surveillance systems, and aggressive response to the occurrence of disease--remains valid. Although it is not clear how important preschool- and college-aged populations are in sustaining transmission independently, recent outbreaks among these groups suggest that additional efforts may be required to implement the elements of the strategy in these groups before measles is completely eliminated in the United States.


  1. Amler RW, Bloch AB, Orenstein WA, et al. Measles in the United States: chains of transmission. 18th Immunization Conference Proceedings, Atlanta, Georgia, CDC, May 16-19, 1983, pp. 17-21.

  2. CDC. Classification of measles cases and categorization of measles elimination programs. MMWR 1982;31:707-11.

  3. CDC. Interstate transmission of measles in a Gypsy population--Washington, Idaho, Montana, California. MMWR 1983;32:659-62.

  4. Amler RW, Kim-Farley RF, Orenstein WA, et al. Measles on campus. J Am College Health 1983;32:53-7.

  5. CDC. Measles among children of migrant workers--Florida. MMWR 1983;32:471-2, 477-8.

  6. Amler RW, Orenstein WA. Measles in young adults. Postgraduate Med (in press).

  7. CDC. Elimination of indigenous measles--United States. MMWR 1982;31:517-9. *Defined in CDC measles case classification (2). **Chain of transmission defined as a series of measles cases consisting of an index case followed by at least two generations of epidemiologically-linked cases. ***Written documentation of date of administration of live measles vaccine on or after the first birthday or of physician-diagnosed measles illness.

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