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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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