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Volume 21, Number 8—August 2015

Dispatch

Geographic Distribution and Expansion of Human Lyme Disease, United States

Kiersten J. KugelerComments to Author , Grace M. Farley, Joseph D. Forrester, and Paul S. Mead
Author affiliations: Centers for Disease Control and Prevention, Fort Collins, Colorado, USA

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Table

Data for United States counties with high incidence of human Lyme disease during four 5-year periods, 1993–2012*

Location, period No. counties Relative risk, range† Average annual incidence, range‡ No. counties added to high-incidence status No. counties removed from high- incidence status
Overall
1993–1997 69 2.3–91.1 10.6–402.7 NA NA
1998–2002 130 2.0–152.6 12.3–912.9 71 10
2003–2007 197 2.0–101.3 15.0–742.8 72 5
2008–2012
260
2.0–48.6
15.9–381.4
72
9
Northeastern focus
1993–1997 43 2.3–91.1 10.6–402.7 NA NA
1998–2002 90 2.0–152.6 12.3–912.9 50 3
2003–2007 130 2.0–101.3 15.0–742.8 45 5
2008–2012
182
2.0–48.6
15.9–381.4
60
8
North-central focus
1993–1997 22 2.6–41.3 12.1–189.6 NA NA
1998–2002 40 2.0–35.3 12.4–217.3 21 3
2003–2007 67 2.0–29.8 15.0–222.7 27 0
2008–2012 78 2.1–28.1 16.1–220.7 12 1

*In the first period, 4 counties in the southeastern United States met high-incidence criteria but are not included in the geographic focus–specific data. NA, not applicable.
†Relative risk is observed number of cases over a period divided by expected number of cases for the population at risk (4). For this analysis, high-incidence counties had a relative risk of >2.0.
‡Incidence is reported cases per 100,000 residents per year; population used was average population at risk during a period (US census data for midpoint of each period).

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