Table 3. Differences in West Nile virus seropositivity in birds by age, region, and habitat using chi-square analysis, Illinois, 2002.
| Comparison | Samples, n (% total); N = 1,784 | Antibody + (%)a | |
|---|---|---|---|
| Habitat | Urban | 524 (29.4%) | 34 (6.49%)A |
| Natural | 1,121 (62.8) | 34 (3.03%)B | |
| Captive | 139 (8.2%) | 26 (18.71%)C | |
| χ2 = 63.06 | p < 0.0001 | ||
| Region | Northern | 412 (23.1%) | 20 (4.85%)D |
| Central | 796 (44.6%) | 62 (7.79%)D | |
| Southern | 576 (32.3%) | 12 (2.08%)E | |
| χ2 = 21.98 | p < 0.0001 | ||
| Ageb | Adult | 455 (25.5%) | 10 (2.2%)F |
| Hatch-year | 508 (28.5%) | 21 (4.1%)F | |
| χ2 = 2.81 | p < 0.096 |
aLike (capital letter) superscripts indicate no difference in pairwise comparisons. b821 of the 1,784 birds had no age recorded at time of collection. The remaining 963 were used for the age analysis.