Table 2.

The association between hemorrhagic fever with renal syndrome (HFRS) incidence and selenium content by multivariate Poisson regression in different climate regions, corrected for other influencing factors (not shown). Region I = temperate monsoon climate; Region II = sub-tropical monsoon climate; Region III = tropical monsoon climate. Region II and Region III were combined due to the small area of Region III. In Region IV (highland hibernal climate) and Region V (temperate continental climate), almost all cases were located in severe selenium-deficient and moderate selenium-deficient areas, except for 2 cases located in non-deficient areas in Region V, not allowing statistical analysis due to the low numbers. IRR is incidence rate ratio. CI is confidence interval.

Variables (Unit)	Region I		Region II & Region III
Selenium content of crops and feed (categorical, ppm)	Adjusted IRR (95% CI)	p-value	Adjusted IRR (95% CI)	p-value
≥0.06 (non-deficient areas)	1	-	1	-
0.03–0.05 (moderate deficient areas)	1.70 (1.27–2.27)	<0.001	0.85 (0.67–1.08)	0.181
≤0.02 (severe deficient areas)	3.45 (2.49–4.79)	<0.001	2.80 (1.92–4.79)	<0.001