Measles -- United States, First 26 Weeks, 1986

During the first 26 weeks of 1986, a provisional total of 3,921 measles cases was reported in the United States, an increase of 117.6% over the 1,802 cases reported during the same period in 1985 (1). The overall incidence rate for the 26-week period in 1986 was 1.7/100,000 population, compared with 0.8/100,000 for 1985. Nine states accounted for 3,185 (81.2%) cases: New Jersey (876), Illinois (412), New York (369), California (299), Arkansas (278), South Carolina (274), Arizona (243), Texas (242), and Wisconsin (192). Eighteen states and New York City had incidence rates greater than 1/100,000 population. Seven states and New York City had incidence rates greater than 3/100,000 population: Arkansas, New Jersey, Arizona, South Carolina, Kansas, Wisconsin, and Illinois. During the first 26 weeks of 1986, 42 states and 9.0% of the nation's 3,139 counties reported measles cases (indigenous or imported), compared with 20 states and 2.5% of the counties in 1985.

Eighty outbreaks (i.e., five or more epidemiologically linked cases) have occurred: nine had more than 100 cases each (three of these had more than 200 cases); five had 51-100 cases each; 11 had 26-50 cases each; and 55 had up to 25 cases.

Detailed information was provided to CDC's Division of Immunization on all 3,921 cases. Of these, 3,824 (97.5%) met the standard case definition for measles*, and 1,174 (29.9%) were serologically confirmed. The number of cases reported weekly began to rise soon after the first of the year and reached a maximum at week 11. The decrease in the number of patients with rash onset after week 21 may be due to a delay in reporting rather than a true decrease (Figure 1).

The incidence rate of measles in all age groups increased substantially between 1985 and 1986. However, the age characteristics of cases differed between the two 26-week periods (Table 1). During the first 26 weeks of 1985, the highest incidence rate was reported for persons 15-19 years of age. By comparison, during the first 26 weeks of 1986, the highest incidence rate occurred among children 0-4 years of age (7.0/100,000), followed by children 10-14 years of age (5.7/100,000). The latter group had the greatest increase in incidence rate between years. Of the 1,249 reported cases among preschool-aged children, 355 (28.4%) were infants under 1 year of age; 212 (17.0%) were 12-14 months of age; 55 (4.4%) were 15 months of age; and 627 (50.2%) were 16 months-4 years of age.

Of the 2,466 (62.9%) patients for whom setting of transmission was reported, 1,371 (55.6%) acquired measles in primary or secondary schools; 203 (8.2%), in colleges or universities; 423 (17.2%), at home; 143 (5.8%), in medical settings; 72 (2.9%), in day care; and 254 (10.3%), in a variety of other settings, including churches, sporting events, and summer camps.

Seventy-three (1.9%) cases were international importations. An additional 41 cases were epidemiologically linked to an international importation within two generations of infection. Therefore, a total of 114 (2.9%) of all cases were programmatically classified as international importations during this period (2). However, it is likely that additional cases--for which source information was not available--were related to international importations.

A total of 1,730 (44.1%) patients had been vaccinated on or after the first birthday, including 724 (18.5%) who were vaccinated at 12-14 months of age. There were 2,001 (51.0%) unvaccinated patients, and 190 (4.8%) with histories of inadequate vaccination (vaccinated before the first birthday).

Of the 3,921 cases, 1,403 (35.8%) were classified as preventable (2) (Table 2). From 1985 to 1986, the absolute number and proportion of cases that were preventable increased in each age group. The highest proportion of preventable cases occurred among persons who were not of school age: 85.0% of cases among children 16 months-4 years of age were preventable (Table 2). Only 28.7% of cases among school-aged persons 5-19 years of age were preventable; however, 44.1% of all preventable cases occurred in this age group.

Of the 2,518 nonpreventable cases, 622 (24.7%) were among persons too young for routine vaccination (under 16 months of age), and 136 (5.4%) were too old (born before 1957). Of the 1,760 who were between 16 months and 29 years of age, 1,658 (94.2%) had been vaccinated on or after the first birthday; one (0.06%) had a prior physician diagnosis of measles; 28 (1.6%) were non-U.S. citizens; and 73 (4.1%) had medical contraindications or exemptions under state law (Table 3). Reported by Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The 3,921 measles cases reported through week 26 of 1986 exceed the total number of reported cases in any year since 1980, when 11,564 cases were reported during the comparable period. The 1986 figure is almost four times higher than the all-time low of 1,037 cases reported during the same period of 1983. Although the number of reported cases still represents less than 1% of that in the prevaccine era, when an average of more than 500,000 cases was reported annually, there is concern about the recent increase.

Incidence rates have increased in all age groups in 1986. The greatest increase (216.7%) occurred among persons 10-14 years of age. The highest incidence rate was in preschoolers who have accounted for almost one-third of all cases in 1986. The large number of cases among children 10-14 years of age was due to several large outbreaks in middle schools this year involving vaccinated students. The large number of cases in preschoolers was due to two large outbreaks in New York City and New Jersey this year in which predominately preschool-aged children were involved, most of whom were unvaccinated (4). The smallest increase in incidence rate was in persons 15-19 years. There were no large outbreaks on college campuses this year as in 1985 (5).

The reasons for the increase in measles cases and the more widespread occurrence this year are not clear. Investigations of various outbreaks this year indicate no single common problem. Rather, a variety of reasons, including vaccine failures and unvaccinated preschoolers, have contributed to the large number of outbreaks.

As the measles elimination strategy is successfully implemented, the proportion of preventable cases should decrease. Since the percentage of preventable cases increased to 36.6% this year from 25.2% in 1985, further improvement in implementing existing recommendations for measles elimination are necessary (6). As in 1984 and 1985, preschool-aged children over 15 months of age comprised the group with the largest proportion of preventable cases. Greater efforts need to be directed at this age group.

References

1. CDC. Measles--United States, first 26 weeks, 1985. MMWR 1986;35:1-4.

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

3. CDC. Measles surveillance report no. 11, 1977-1981. Atlanta, Georgia: Centers for Disease Control, 1982.

4. CDC. Measles--New Jersey. MMWR 1986;35:213-5.

5. CDC. Measles on college campuses--United States, 1985. MMWR 1985;34:445-9.

6. ACIP. Measles prevention. MMWR 1982;31:217-24, 229-31. *Fever (38.3 C (101 F) or higher, if measured), generalized rash of 3 days or longer duration, and at least one of the following: cough, coryza, conjunctivitis.

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