Volume 13, Number 3—March 2007
Research
Risk for Infection with Highly Pathogenic Influenza A Virus (H5N1) in Chickens, Hong Kong, 2002
Nina Y. Kung*†1
, Roger S. Morris*, Nigel R. Perkins*, Les D. Sims‡, Trevor M. Ellis‡, Lucy Bissett‡, Mary Chow‡, Ken F. Shortridge‡, Yi Guan‡, and Malik J.S. Peiris‡
, Roger S. Morris*, Nigel R. Perkins*, Les D. Sims‡, Trevor M. Ellis‡, Lucy Bissett‡, Mary Chow‡, Ken F. Shortridge‡, Yi Guan‡, and Malik J.S. Peiris‡Table 3
Results of univariate analysis of risk factors for avian influenza type A virus (H5N1) infection among chicken farms, Hong Kong, 2002*
| Variable | Category | Case | Control | OR | 95% CI | p value |
|---|---|---|---|---|---|---|
| Farm profile | Pig farm within 500 m | 13 | 29 | 2.54 | 0.63–10.21 | 0.226 |
| No pig farm within 500 m | 3 | 17 | 1 | |||
| Stock | No. chickens on the farm | NA | NA | NA | NA | <0.001 |
| Stock density (chicken no./farm area ) | NA | NA | NA | NA | 0.007 | |
| Age group with highest death rate | Most deaths in birds ≥30 d old | 5 | 3 | 7.40 | 1.49–36.82 | 0.017 |
| Most deaths in birds <30 d old | 9 | 40 | 1 | |||
| Survival rate | ≥90% at 1–30 d | 15 | 28 | 1.54 | 1.23–1.91 | 0.003 |
| <90% at 1–30 d | 0 | 18 | 1 | |||
| ≥90% at 30–60 d | 11 | 42 | 0.26 | 0.06–1.22 | 0.093 | |
| <90% at 30–60 d | 4 | 4 | 1 | |||
| ≥90% at >60 d | 13 | 44 | 0.20 | 0.03–1.31 | 0.103 | |
| <90% at >60 d | 3 | 2 | 1 | |||
| Medication given? (Jan–Feb 2002) | Yes | 12 | 18 | 4.67 | 1.30–16.74 | 0.020 |
| No | 4 | 28 | 1 | |||
| Were wild birds seen eating in feed troughs? | Yes | 10 | 41 | 0.20 | 0.04–0.86 | 0.036 |
| No | 5 | 4 | 1 | |||
| Could wild birds gain entry into the shed? | Yes | 13 | 44 | 0.10 | 0.01–1.03 | 0.052 |
| No | 3 | 1 | 1 | |||
| Does the farm sell chickens directly to a retail market? | Yes | 7 | 3 | 11.15 | 2.41–51.56 | 0.002 |
| No | 9 | 43 | 1 | |||
| Installed automatic manure scrapers in shed | Yes | 11 | 15 | 4.55 | 1.34–15.46 | 0.018 |
| No | 5 | 31 | 1 | |||
| Farm owner lives on farm | Yes | 7 | 43 | 0.05 | 0.01–0.25 | <0.001 |
| No | 9 | 3 | 1 | |||
| Farm owner owns or partly owns another chicken farm | Yes | 3 | 2 | 5.08 | 0.77–33.71 | 0.103 |
| No | 13 | 44 | 1 | |||
| Farmer has relatives working in the poultry industry | Yes | 4 | 5 | 2.73 | 0.63–11.81 | 0.219 |
| No | 12 | 41 | 1 | |||
| Visitors from another chicken farm? | Yes | 2 | 0 | 0.23 | 0.15–0.37 | 0.015 |
| No | 14 | 46 | 1 | |||
| Visitors from retail markets? | Yes | 5 | 2 | 10.00 | 1.71–58.59 | 0.010 |
| No | 11 | 44 | 1 | |||
| Visitors went inside sheds? | Yes | 7 | 8 | 3.94 | 1.03–15.13 | 0.040 |
| No | 6 | 27 | 1 | |||
| District | Within main affected area | 15 | 5 | 123.00 | 13.27–1140.46 | 0.000 |
| Outside main affected area | 1 | 41 | 1 |
*Variables for which p value is >0.25 have been excluded. OR, odds ratio; CI, confidence interval; NA, not applicable.
