ATLANTA - The largest U.S. outbreak of measles since 1996 was recently reported in Alaska by the Centers for Disease Control and Prevention (CDC).
The CDC confirmed that 33 cases occurred in Anchorage, Alaska between Aug. 10 and Nov. 23, 1998. Quick action to vaccinate students probably contained the outbreak, the CDC added. Patients ranged in age from 2 to 28 years, but most were in high school. There were no serious complications or deaths.
The index case was a 4-year-old child visiting from Japan who had an onset of rash that was reported on Aug. 10. The child spent one day in the hospital while the diagnosis was made. Measles was confirmed by positive rubeola IgM enzyme-linked im mu no sorbet assay (ELISA), but the hospital staff did not obtain viral cultures. The strain that caused the outbreak was almost identical to wild viral strains that were circulating in Japan last year.
In an unusual turn of events, no other cases were reported until Sept. 5, more than three weeks following the index case. People are infectious from seven days before to four days after the onset of a measles rash, so one would have expected secondary cases to occur within 21 days, the CDC said.
Twenty-six days days after the onset of the first case, a teenager developed a measles rash. Subsequently, 15 other students and one teacher at the same high school developed measles. Twelve of the cases were laboratory confirmed.
In addition, six cases occurred at other Anchorage schools, eight cases were found among young adults outside of a school setting, and one case occurred in a 2-year-old.
Twenty-nine patients had received at least one dose of measles-containing vaccine (MCV) but not a second dose. The outbreak summarized recently in the Morbidity and Mortality Weekly Report "under-scores the importance of second-dose requirements for measles vaccine," the CDC said. Only one patient had received two doses of measles-mumps-rubella (MMR) vaccine.
Before 1996, it was an entry requirement of all Alaskan public and private schools that students could document receiving a single dose of MCV or had a valid medical or religious exemption. Beginning in September 1996, all kindergarten and first grade students were required to have two doses of MCV. As a result, almost all Alaskan students in kindergarten through third grade have received two doses of MMR. However, the CDC did not know how many students in the upper grades had received two doses of measles vaccine.
In response to the outbreak, the health department issued an emergency order requiring that all school children have two doses of MCV. By Nov. 17, 98.6% of 49,346 Anchorage students had provided documentation of two doses of MCV. "The vigorous response by public health and school officials in Anchorage to this outbreak in accelerating second-dose measles vaccination among schoolchildren may have limited the extent of this outbreak and will help prevent future outbreaks in Alaska schools," the CDC said.
The CDC said it was important for doctors to obtain throat and urine specimens from suspected measles cases immediately after rash onset to type the virus for measles surveillance. Although there is no endemic measles virus circulating in the United States, outbreaks may occur when imported virus is introduced to children who have only received one dose of a measles-containing vaccine.
For more information:
- CDC. Transmission of Measles Among a Highly Vaccinated School Population - Anchorage, Alaska, 1998. MMWR. 1999;48:1109-12.
- CDC. Measles-United States, 1997. MMWR. 1998;47:273-6.
- CDC. Measles-United States, 1996, and the interruption of indigenous transmission. MMWR. 1997;46:242-6.
- WHO. Expanded programme on immunization (EPI) - standardization of the nomenclature for describing the genetic characteristics of wild-type measles viruses. Wkly Epidemiol Rep. 1998;73:265-9.
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