National Lyme Disease Risk Map (4 June 1999)

Originally published


Lyme disease risk is measurable as a function of two epidemiologic parameters entomologic risk and human exposure. Entomologic risk for Lyme disease is defined as the density per unit area of host-seeking nymphal ticks infected with Borrelia burgdorferi. Field studies needed for determination of entomologic risk require trained entomologists, and such studies are limited to a narrow seasonal window within the life-cycle of vector ticks. Limited resources preclude the direct measurement of entomologic risk over large geographic areas; therefore, indirect measures were used to estimate risk to develop this national Lyme disease risk map. First, data on vector distribution, abundance, B. burgdorferi infection prevalence, and human exposure were compiled on a county-unit scale for the United States. Then geographic information systems (GIS) technology was used to combine these data and categorize each of the 3,140 counties into four risk classes.
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