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).