Table 3. Multivariate analysis of Ac Mong encephalitis, Bac Giang Province, Vietnam, 2004–2009.

Variable/category	IRR* (95% CI)	p value†
Litchi surface, % commune surface
<1.49	1	<0.001
1.49–5.84	1.52 (0.90–2.57)
5.84–12.92	2.94 (1.88–4.60)
>12.92	2.76 (1.76–4.32)
Poultry density, no./km2
<1,449.79	1	<0.001
1,449.79–3,715.18	0.62 (0.43–0.91)
3,715.18–7,065.25	0.61 (0.42–0.89)
>7,065.25	0.25 (0.15–0.43)
Mean humidity, %, January–April
<82.07	1	<0.001
82.07–83.55	0.84 (0.61–1.16)
>83.55	0.35 (0.23–0.54)

*IRR, incidence rate ratio.
†Indicates global p value.