. 2009 Dec 16;41(3):28. doi: 10.1051/vetres/2009076

Table I.

Results of the multivariate analysis for factors associated with risk of HPAI H5N1 in chicken and duck flocks from 3 July 2004 to 5 May 2005 in Thailand (p ≤ 0.05).

Variable	Categories	Number of subdistricts	Chicken flocks		Duck flocks
Variable	Categories	Number of subdistricts	Risk ratio	95% CI	Risk ratio	95% CI
(a) Environmental factors
Relative risk for ducks
	≤ 0.5	2 769	1.00
	0.51–1.5	825	0.76	0.63–0.91
	1.51–10	1 310	1.86	1.55–2.22
	≥ 10.01	2 462	13.11	10.92–15.73
Relative risk for chickens
	≤ 0.5	3 175			1.00
	0.51–1.5	633			1.10	0.86–1.42
	1.51–10	1 824			6.13	4.83–7.78
	≥ 10.01	1 734			33.86	26.33–43.53
Average altitude (m)
	≥ 400.01	632	1.00		1.00
	150.01–400	2 605	0.38	0.32–0.45	0.27	0.21–0.34
	50.01–150	1 701	0.53	0.45–0.63	0.24	0.19–0.30
	≤ 50	2 428	5.73	4.77–6.90	10.16	7.89–13.09
Mean number of rice crops per year
	≤ 0.2	1 167	1.00		1.00
	0.21–1	2 405	0.77	0.65–0.92	0.88	0.70–1.10
	1.01–1.5	3 308	1.47	1.24–1.76	1.12	0.88–1.42
	≥ 1.51	486	11.21	9.15–13.73	17	12.89–22.42
Distance to the closest river (km)
	≥ 10.01	1 328	1.00		1.00
	5.01–10	1 509	0.68	0.57–0.82	0.59	0.47–0.75
	2.01–5	1 966	0.83	0.69–0.99	0.74	0.58–0.94
	≤ 2	2 563	2.05	1.71–2.46	2.88	2.25–3.69
(b) Poultry farming factors
Density of native chickens (no poultry/km²)
	≤ 50	1 441	1.00		1.00
	50.01–100	1 324	1.12	0.94–1.33	1.57	1.24–2.00
	100.01–300	3 319	0.73	0.61–0.87	0.52	0.41–0.66
	≥ 300.01	1 282	0.52	0.43–0.63	0.46	0.36–0.60
Density of fighting cocks (no poultry/km²)
	≤ 0.1	4 191	1.00		1.00
	0.11–1	1 682	0.59	0.50–0.71	0.53	0.42–0.67
	1.01–3	832	0.75	0.62–0.91	0.62	0.48–0.80
	≥ 3.01	661	1.52	1.24–1.87	2.3	1.75–3.03
Density of houses with fighting cocks (no house/km²)
	≤ 0.01	3 152	1.00		1.00
	0.01–0.1	2 163	0.67	0.56–0.79	0.69	0.55–0.87
	0.11–0.4	1 439	0.86	0.71–1.04	0.73	0.57–0.94
	≥ 0.41	612	1.26	1.01–1.54	1.59	1.21–2.10
Density of free-grazing ducks (no poultry/km²)
	≤ 0.1	5 953	1.00		1.00
	0.11–10	779	0.68	0.57–0.83	0.37	0.29–0.48
	≥ 10.01	634	10.13	8.29–12.37	18.26	13.88–24.04
Density of farms with free-grazing ducks (no farm/km²)
	≤ 0.001	4 539	1.00		n.s.	n.s.
	0.0011–0.05	1 367	0.65	0.54–0.78	n.s.	n.s.
	≥ 0.051	1 460	1.61	1.33–1.96	n.s.	n.s.
Density of broiler and layer chickens (no poultry/km²)
	≤ 1	2 997	n.s.	n.s.	1.00
	1.01–50	2 475	n.s.	n.s.	0.78	0.61–0.98
	50.01–500	1 076	n.s.	n.s.	0.68	0.53–0.88
	≥ 500.01	818	n.s.	n.s.	3.04	2.34–3.95
Density of farms with broiler and layer chickens (no farm/km²)
	≤ 0.01	932	1.00		1.00
	0.011–0.05	1 092	0.78	0.65–0.93	0.75	0.59–0.94
	0.051–1	4 794	1.01	0.85–1.21	1.03	0.81–1.31
	≥ 1.01	548	0.61	0.50–0.75	0.66	0.50–0.87
Density of broiler and layer ducks (no poultry/km²)
	≤ 5	3 374	1.00		1.00
	5.01–20	2 195	0.96	0.80–1.15	0.62	0.49–0.79
	20.01–80	1 222	0.97	0.81–1.17	0.51	0.39–0.65
	≥ 80.01	575	4.6	3.76–5.63	6.85	5.19–9.04
Density of farms with broiler and layer ducks (no farm/km²)
	≤ 0.5	3 228	1.00		1.00
	0.51–1	1 471	1.41	1.18–1.69	1.32	1.03–1.69
	1.01–2	1 423	1.22	1.02–1.47	0.88	0.69–1.13
	≥ 2.01	1 244	0.7	0.58–0.84	0.28	0.22–0.36
(c) Anthropogenic factors
Road density
	≤ 0.001	1 897	1.00		1.00
	0.0011–0.002	1 849	0.73	0.61–0.87	0.68	0.54–0.86
	0.0021–0.005	2 538	0.69	0.58–0.82	0.46	0.36–0.58
	≥ 0.0051	1 082	4	3.32–4.82	6.82	5.29–8.80
Density of human population (km²)
	≤ 100	2 206	1.00		1.00
	100.01–300	3 744	0.86	0.72–1.02	0.57	0.45–0.72
	300.01–600	758	2.61	2.15–3.18	4.18	3.19–5.46
	≥ 600.01	658	5.56	4.62–6.68	11.61	9.04–14.90
Distance to the closest highway (km)
	≥ 50.01	1 021	1.00		1.00
	20.01–50	2 109	0.76	0.64–0.91	0.52	0.41–0.66
	5.01–20	2 494	1.19	0.99–1.43	1.28	1.01–1.64
	≤ 5	1 742	1.96	1.63–2.35	2.84	2.21–3.63
Distance to the closest highway junction (km)
	≥ 100.01	1 964	1.00		1.00
	50.01–100	2 569	0.78	0.66–0.94	0.78	0.61–0.99
	20.01–50	1 863	2.09	1.75–2.51	2.81	2.19–3.60
	≤ 20	970	6.15	5.13–7.38	9.46	7.38–12.13
Distance to the closest major city (km)
	≥ 80.01	3 427	1.00		1.00
	40.01–80	2 176	1.15	0.96–1.37	1.02	0.80–1.30
	20.01–40	965	1.78	1.48–2.15	2.06	1.60–2.66
	≤ 20	798	4.14	3.44–4.98	7.12	5.53–9.15