Table 5.
Relative risk of seroconversion estimated from four Cox regression models*
| Variable | P value | Relative risk |
|---|---|---|
| 1-km model 1–14 days prior | ||
| Year 2004 | < 0.001 | 5.860 |
| Year 2007 | < 0.001 | 0.135 |
| Year 2008 | 0.003 | 3.161 |
| Wild bird seroconversion rate | 0.103 | 0.408 |
| Dead bird reports | 0.074 | 1.130 |
| Average minimum temperature | 0.046 | 1.318 |
| Degree days | 0.018 | 1.025 |
| 1-km model 15–28 days prior | ||
| Year 2005 | 0.057 | 0.474 |
| Year 2006 | < 0.0001 | 0.117 |
| Year 2007 | < 0.0001 | 0.12 |
| Wild bird seroconversion rate | 0.0061 | 0.032 |
| Average maximum temperature | 0.0258 | 1.283 |
| Degree days | 0.0429 | 1.019 |
| 5 km model 1–14 days prior | ||
| Year 2004 | < 0.0001 | 5.893 |
| Year 2007 | 0.0004 | 0.126 |
| Year 2008 | 0.0038 | 3.062 |
| Wild bird cumulative seroprevalence | 0.1162 | 3.147 |
| Wild bird seroconversion rate | 0.0145 | 0.166 |
| Average minimum temperature | 0.0532 | 1.308 |
| Degree days | 0.0113 | 1.027 |
| 5 km model 15–28 days prior | ||
| Year 2004 | < 0.001 | 9.896 |
| Year 2005 | 0.016 | 3.656 |
| Year 2008 | < 0.001 | 14.028 |
| Wild bird seroconversion rate | 0.004 | 0.019 |
| Positive mosquito pool | 0.075 | 0.452 |
| Positive dead bird | 0.002 | 1.074 |
| Average maximum temperature | 0.004 | 1.451 |
| Degree days | 0.049 | 1.019 |
*
The most proximal model to sentinel chicken seroconversions included covariates within the 1-km spatial sampling radius and the 1–14 day antecedent temporal lag, whereas the most distal model included covariates from within the 5-km spatial sampling zone and the 15–28 day antecedent temporal lag.