A Study of the Persistence of Mycobacterium bovis in the Environment under Natural Weather Conditions in Michigan, USA

Table 4

Cox’s proportional hazard regression model for persistence of M. bovis over three different sampling periods (Fall/Winter “A”, Winter/Spring “B” and Spring/Summer “C”) or seasons.

Risk factor	Parameter estimate	Standard error	Hazard ratio (95% confidence interval)
Season A	−2.13	0.49	0.12 (0.05–0.32)
Season B	−1.94	0.49	0.14 (0.5–0.38)
Season C	0	—	—
Sample Type	−0.28	0.16	0.76 (0.55–1.05)
Sterilized	−0.50	0.35	0.61 (0.31–1.20)
Shade	−0.68	0.33	0.51 (0.26–1.05)