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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*†1Comments to Author , 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‡
Author affiliations: *Massey University, Palmerston North, New Zealand; †University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, People’s Republic of China; ‡Department of Agriculture, Fisheries and Conservation, Kowloon, Hong Kong Special Administrative Region, People’s Republic of China;

Main Article

Table 3

Results of univariate analysis of risk factors for avian influenza type A virus (H5N1) infection among chicken farms, Hong Kong, 2002*

VariableCategoryCaseControlOR95% CIp 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 area1411

*Variables for which p value is >0.25 have been excluded. OR, odds ratio; CI, confidence interval; NA, not applicable.

Main Article

1Current affiliation: AgriQuality Ltd, Lower Hutt, New Zealand

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