Measles -- United States, First 26 Weeks, 1993

As of July 3, 1993 (week 26), local and state health departments had reported a provisional total of 167 measles cases for 1993 (1) -- the lowest total reported for the first 26 weeks of any year since surveillance began in 1943 and a 99% decrease from the 13,787 cases reported during the first 26 weeks of 1990, the peak of the recent resurgence (2). Cases were reported from 18 states. This report summarizes the epidemiologic characteristics of measles cases reported for the first 26 weeks of 1993 and compares them with cases reported during 1989-1991. Characteristics

In addition to the 167 measles cases reported through CDC's National Notifiable Diseases Surveillance System (NNDSS), eight additional cases not reported through NNDSS as of week 26 were identified by CDC's National Immunization Program. Of these 175 reported measles cases, 102 (58%) were acquired indigenously; one case was acquired in Puerto Rico. Of 14 (8%) imported cases, the country of acquisition was known for 12: five were acquired in Germany, two in Japan, and one each in Haiti, Liberia, the Philippines, Sierra Leone, and El Salvador. A total of 58 (33%) cases were epidemiologically linked to imported cases.

Of the 98 (56%) cases for which serologic testing for measles was reported, 93 were serologically confirmed. Although the other five cases were seronegative, all met the standard CDC case definition for measles (3).

Of the 175 case-patients, 54 (31%) were aged less than 5 years, including 17 (10%) aged less than 12 months. In addition, 77 (44%) case-patients were aged 5-19 years, and 44 (25%) were aged greater than or equal to 20 years (Table_1). Vaccination Status

Overall, 39 (22%) reported case-patients had received one dose of measles-containing vaccine on or after the first birthday; no cases were reported among persons who had received two doses of vaccine. A total of 47 (27%) reported case-patients were unvaccinated but vaccine-eligible (i.e., U.S. citizens aged greater than or equal to 16 months without medical, religious, or philosophic exemption to vaccination) (Table_1). Other unvaccinated groups included 35 (20%) persons with philosophic exemption to vaccination, 30 (17%) who were aged less than 16 months, 10 (6%) who were born before 1957, and 10 (6%) who were non-U.S. citizens. Vaccination status varied by age group: 36% of persons aged 5-19 years were adequately vaccinated, compared with 14% of children aged 1-4 years (Table_1). Outbreaks

The largest measles outbreaks were reported from California (Los Angeles County {29 cases} and Sonoma County {40 cases}) and Vermont (Chittenden County {20 cases}). In all three counties, 60%- 78% of cases occurred among school-aged persons (i.e., aged 5-19 years). In the Los Angeles County and Chittenden County outbreaks, previous receipt of one dose of measles-containing vaccine was documented for 40% and 82% of school-aged persons, respectively. In Sonoma County, the outbreak involved an alternative-lifestyle community; because most persons claimed philosophic exemption to vaccination, 95% were unvaccinated. The index patient of this outbreak had acquired measles in Germany.

Two small outbreaks were reported from Connecticut (Hartford County {seven cases}) and Honolulu (nine cases). In Hartford County, four of the seven cases occurred among adults aged greater than or equal to 25 years; although the specific source of the outbreak was unidentified, it probably was related to ongoing measles transmission in Puerto Rico. In Honolulu, seven of the nine cases occurred among preschool-aged children; the index patient of this outbreak had acquired measles in the Philippines. Reported by: State and local health depts. M Nelson, PhD, L Dales, MD, Immunization Br, California Dept of Health Svcs. P Frederick, MPH, Los Angeles County Dept of Health Svcs, Los Angeles. R Houseknecht, PhD, State Epidemiologist, Vermont Dept of Health. P Lamb, Connecticut State Dept of Public Health and Addiction Svcs. National Immunization Program, CDC.

Editorial Note

Editorial Note: During 1989-1991, widespread measles activity occurred in the United States; however, in 1992, reported measles cases decreased sharply (4). The sustained decline during the first 26 weeks of 1993 represents the lowest total of reported measles cases in the history of measles surveillance in the United States. From 1985 through 1992, an average of 54% of the annual total of measles cases had been reported by week 26 (range: 47%-67%) (CDC unpublished data, 1993). Based on current reporting trends--and if no large outbreaks occur -- fewer than 500 measles cases may be reported in 1993.

During 1993, measles cases have involved predominantly school-aged persons, and the largest outbreaks have occurred among school-aged persons who had received one dose of measles vaccine (i.e., vaccine failures). In contrast, during 1989-1991, cases involved predominantly preschool-aged children, and the largest outbreaks occurred among unvaccinated preschool-aged children living in large urban areas (5-7). In addition, during 1993, the largest measles outbreak among predominantly preschool-aged children has involved nine cases in Hawaii; during 1989-1991, several outbreaks among such children involved more than 1000 cases.

The decline in measles incidence during 1992 and 1993 most likely reflects increased measles vaccination coverage levels among preschool-aged children. The estimated level of measles vaccination coverage for children aged 2 years was substantially higher in 1991 (83%) than in 1985 (61%) (8) (CDC, unpublished data, 1993). In addition, this decline may reflect a decrease in measles importation from other countries in the Western Hemisphere associated with aggressive measles-control programs.

The risk for measles outbreaks among school-aged persons and college entrants can be reduced through systematic efforts to introduce and enforce vaccination with a second dose of measles vaccine among members of these age groups (9). In addition, efforts must be continued to further increase measles vaccination levels among preschool-aged children to ensure against the recurrence of measles outbreaks among young children in urban settings.

Although the low reported incidence of measles during the first 26 weeks of 1993 suggests that transmission has been interrupted in many parts of the United States, the report of 102 indigenous cases without a known source indicates that undetected transmission is occurring in some areas. Reports of individual cases of measles should be immediately and thoroughly investigated and, when possible, serologically confirmed; rapid implementation of appropriate vaccination strategies can prevent small clusters of cases from becoming large outbreaks.

References

1. CDC. Table II. Cases of selected notifiable diseases, United States, weeks ending July 3, 1993, and June 27, 1992 (26th week). MMWR 1993;42:510.

2. CDC. Table II. Cases of specified notifiable diseases, United States, weeks ending June 30, 1990, and July 1, 1989 (26th week). MMWR 1990;39:448.

3. CDC. Case definitions for public health surveillance. MMWR 1990;39(no. RR-13):23.

4. CDC. Measles -- United States, 1992. MMWR 1993;42:378-81.

5. Atkinson WL, Orenstein WA, Krugman S. The resurgence of measles in the United States, 1989-1990. Annu Rev Med 1992;43:451-63.

6. Gindler JS, Atkinson WL, Markowitz LE, Hutchins SS. Epidemiology of measles in the United States in 1989 and 1990. Pediatr Infect Dis J 1992;11:841-6.

7. Atkinson WL, Hadler SC, Redd SB, Orenstein WA. Measles surveillance -- United States, 1991. In: CDC surveillance summaries (November). MMWR 1992;41(no. SS-6):1-12.

8. Bureau of the Census. Statistical abstract of the United States, 1993. 113th ed. Washington, DC: US Department of Commerce, Bureau of the Census, 1993.

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

Table_1
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TABLE 1. Age and vaccination status of 175 reported measles case-patients -- United
States, first 26 weeks, 1993
========================================================================================================
                                                          Unvaccinated
                                            -----------------------------------------
                     Vaccinated *                         Not routinely
              -------------------------      Vaccine-     eligible for
               2 doses         1 dose       eligible +    vaccination &      Other @         Total
Age group     ----------     ----------     ----------    -------------    ----------     ------------
  (yrs)       No.   (%)      No.   (%)      No.   (%)      No.    (%)      No.   (%)       No.    (%)

 <12 mos      NE **  --      NE     --      NE     --      17    (100)     NE     --       17    ( 10)
1- 4 yrs       0     --       5    (14)      8    (22)     14 ++ ( 38)     10 && (27)      37    ( 21)
5-19 yrs       0             28    (36)     18    (23)      0      --      31 && (40)      77    ( 44)
>=20 yrs       0     --       6    (14)     21    (48)     11    ( 25)      6    (14)      44    ( 25)

Total          0     --      39    (22)     47    (27)     42    ( 24)     47    (27)     175    (100)
------------------------------------------------------------------------------------------------------
 * At least one dose of measles-containing vaccine on or after the first birthday.
 + U.S. citizens aged >=16 months without medical, religious, or philosophic exemption to
   vaccination.
 & Persons aged <16 months, born before 1957, with medical contraindication, or with
   documented physician or serologic evidence of measles immunity.
 @ Non-U.S. citizens and persons with religious or philosophic exemption to vaccination.
** Not eligible.
++ Thirteen (93%) case-patients were aged <16 months (i.e., less than the routine age of
   vaccination).
&& Seven (70%) 1-4-year-olds and 28 (90%) 5-19-year-olds in this category had philosophic
   exemption to vaccination.
========================================================================================================

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