KEYWORDS:
Pertussis; School immunization exemptions; geo-coded data

BACKGROUND:
In 1998 the per capita incidence of 112.7 pertussis cases/100,000 for an island community in King County, Washington was significantly different from a rate of 9.4cases/100,000 for King County overall (p<0.001). In addition, school immunization exemption rates in the three island public schools were high. This situation prompted Public Health-Seattle & King County to assess the relationship and potential impact of high levels of school immunization exemption rates on pertussis incidence in the entire county.

OBJECTIVE(S):
To evaluate the relationship between high levels of school immunization exemption rates and the incidence of pertussis disease in the community.

METHOD(S):
Pertussis cases for 1998-2000 and school exemption rates for the 1999-2000 school year were geo-coded and plotted on maps divided by the seventeen school districts in King County. Clusters of pertussis disease were identified and compared to school exemption rates in the school district.

RESULT(S):
School districts with exemption rates higher than the county average had consistently higher incidence of pertussis disease. However, one school district had high incidence of disease over the three year time period, yet had school exemption rates that were lower than the county average.

CONCLUSIONS(S):
In the island community, there is a correlation between high immunization exemption rates and incidence of pertussis. Our analysis also suggests other areas of the county with a relationship between high immunization exemption rates and incidence of pertussis. Problems with the school exemption data quality in King County include lack of immunization record validation and lack of reporting by approximately 10% of schools. Lack of exemption reports, especially from private schools, may explain areas of high disease incidence but low exemption rates.

LEARNING OBJECTIVES:
To evaluate the relationship between high school immunization exemption rates and disease incidence in a community.