Measles Outbreak in Rural Washington State Requiring Measles Control Efforts in Urban King County

Background:
Measles is a potentially severe vaccine-preventable disease that was once a common childhood experience. Routine vaccination of all children has dramatically reduced measles incidence in the United States from an estimated 3-4 million cases per year to a record low of 37 cases in 2004. During the first half of 2008 over 130 cases were reported, 92% of which were unvaccinated or had an unknown immunization status.

Setting:
Since measles was declared no longer endemic in the United States in 2000, Washington State has identified 0 – 15 cases per year, all either imported or with a clear link to an imported case.

Population:
The 2006 population estimate for Washington State was 6,395,798, just over 2 percent of that for the United States. Measles vaccination coverage (1 MMR) estimates among Washington's children aged 19--35 months in 2007 was 90.5%. Measles vaccination coverage for Washington adults is not known. Exemptions to vaccination requirements for school entry have now exceeded 5% statewide.

Project Description:
In April, 2008 Grant County Health District (GCHD) reported eight measles cases to the Washington State Department of Health (DOH), three of whom had attended an event in King County, Washington during the likely exposure period for the index case. Public Health – Seattle & King County (PHSKC) worked with event organizers to notify over 3000 attendees from 12 states and 3 countries of possible measles exposures at the conference. One of eleven additional Grant County cases identified participated in a trip to King County while contagious. Follow-up with 45 employees at 3 public sites and a public notice were required.

Results/Lessons Learned:
Measles control efforts may be required in nearby metropolitan health districts even when none of their residents contract measles. Eighteen of the Grant County residents with measles were children, and none of the school-aged cases had received any measles-containing vaccine.