Volume 14, Number 10—October 2008
Research
Ecologic Factors Associated with West Nile Virus Transmission, Northeastern United States
Table 2
Odds ratios for median split incidence of West Nile virus diseases in humans, for significant variables*
| Predictor | Adjusted |
Unadjusted |
|||
|---|---|---|---|---|---|
| OR (95% CI) | Significance | OR (95% CI) | Significance | ||
| % Forest land use, per quartile | |||||
| 1st (<38.29) | 4.40 (1.91–10.11) | 0.000 | 4.36 (1.44–13.25) | 0.009 | |
| 2nd (38.29–56.56) | 3.09 (1.38–6.92) | 0.006 | 2.86 (1.01–8.06) | 0.047 | |
| 3rd (56.56–69.59) | 0.84 (0.37–1.91) | 0.675 | 0.81 (0.33–2.00) | 0.644 | |
| 4th (>69.59) |
1 |
NA |
1 |
NA |
|
| % Urban land use, per quartile | |||||
| 1st (<1.68) | 1 | NA | 1 | NA | |
| 2nd (1.68–4.66) | 1.52 (0.68 - 3.39) | 0.309 | 1.42 (0.54–3.76) | 0.478 | |
| 3rd (4.66–15.13) | 2.44 (1.09 - 5.43) | 0.030 | 3.08 (0.94–10.12) | 0.064 | |
| 4th (>15.13) | 4.38 (1.91- 10.03) | 0.000 | 7.02 (1.78–27.71) | 0.031 | |
*Variables categorized by percent of county classified as forested and percent of county classified as urban. Outcome categorized by median split to counties with low risk (incidence <0.75 cases/100,000 residents) and high risk (incidence >0.75 cases/100,000 residents). Overall trend is for increasing incidence with increasing measures of urbanization (for decreasing percentage forested land: χ2 = 9.47, df = 1, p< 0.01, goodness of fit χ2 = 3.50, df = 2,
p = 0.17; for increasing percentage urban land: χ2 = 7.13, df = 1, p< 0.01, goodness of fit χ2 = 1.98, df = 2, p = 0.37). Both unadjusted and surveillance bias and spatial relationship adjusted ORs are provided. OR, odds ratio; CI, confidence interval; NA, not applicable.