Table 1. Matched-pair analysis of potential risk factors for highly pathogenic avian influenza virus (H5N1) in backyard chickens, Bangladesh, 2007.
| Risk factor | Case farms (n = 25), no. (%) | Control farms (n = 75), no. (%) | Matched OR (95% CI)* | p value |
|---|---|---|---|---|
| Farm <5 km from nearest veterinary hospital | 15 (60.0) | 41 (54.7) | 1.3 (0.5–3.2) | 0.636 |
| Nearby (<0.1 km) body of water | 16 (64.0) | 23 (30.7) | 3.7 (1.5– 9.5) | 0.004 |
| Farm <0.5 km from larger body of water | 15 (60.0) | 50 (66.7) | 0.7 (0.3–1.9) | 0.543 |
| Commercial farm within 0.5 km | 9 (36.0) | 44 (58.7) | 0.3 (0.1–0.9) | 0.028 |
| Migratory birds seen around farm | 6 (24.0) | 5 (6.7) | 7.5 (1.5–38.7) | 0.010 |
| Local live bird market within <5-km radius | 24 (96.0) | 73 (97.3) | 0.7 (0.1–7.4) | 0.747 |
| Farm <1 km from live bird market | 17 (68.0) | 50 (66.7) | 1.1 (0.4–3.0) | 0.895 |
| Contact with ducks | 22 (88.0) | 55 (73.3) | 4.0 (0.8–20.1) | 0.062 |
| Contact with pigeons | 16 (64.0) | 21 (28.0) | 5.5 (1.9–16.0) | 0.001 |
| Presence of rodents | 12 (48.0) | 9 (12.0) | 5.8 (2.0–16.8) | 0.001 |
| Chickens and ducks on the same farm | 11 (44.0) | 40 (53.3) | 0.7 (0.3–1.7) | 0.415 |
| Chickens and ducks in different night shelters | 2 (8.0) | 31 (41.3) | 0.1 (0.1–0.5) | 0.001 |
| Frequent (≈1×/wk) cleaning of shelter | 18 (72.0) | 44 (58.7) | 1.8 (0.7–4.9) | 0.221 |
| No disinfection in shelter | 4 (16.0) | 10 (13.3) | 3.0 (0.2–48.0) | 0.448 |
| Disposal of bird in open space | 19 (76.0) | 58 (77.3) | 0.9 (0 .3– 3.2) | 0.869 |
| Recently purchased chickens brought in† | 5 (20.0) | 10 (13.3) | 1.7 (0.5–5.7) | 0.421 |
| Offering slaughter remnants of purchased chickens† | 8 (32.0) | 2 (2.7) | 22.1 (2.7–177.7) | 0.000 |
| Death of neighbor’s chickens | 7 (28.0) | 20 (26.7) | 1.1 (0.4–2.8) | 0.900 |
| Source of chicks = own hatched | 5 (20.0) | 20 (26.7) | 0.4 (0.1–2.0) | 0.226 |
*Matched-pair analysis using McNemar (Mantel-Haenszel) test statistics. OR, odds ratio; CI, confidence interval. †Within 21 days of the onset clinical signs on case backyard farms.