TABLE 3.

Multivariate logistic regression model for herd-level risk factors associated with fecal shedding of E. coli O157:H7 in 20 California cow-calf operations between 2012 and 2013

Factor	Coefficient	Odds ratio	P valuea	95% CI
Stocking density of herdb	0.077	1.08	0.02	1.01–1.15
Length of calving season (days)c	−0.037	0.96	0.01	0.94–0.99
Season for herd visit
Spring	−1.96	0.14	0.001	0.05–0.43
Summer	−3.10	0.05	0.02	0.003–0.62
Fall	−0.32	0.73	0.56	0.25–2.14
Winterd	0.0	1.0	—e	—
Cattle access to surface water source(s)
Nod	0.0	1.0	—	—
Yes	1.44	4.2	0.01	1.38–13.04
Constant		0.18	0.03	0.04–0.88

^aP values adjusted for potential intraherd correlation of E. coli O157:H7 shedding status.

^bAdult cattle, heifers, and calves all counted as individual head of cattle.

^cNumber of days for 75% of calves to be born.

^dReferent category.

^e—, not applicable.