TABLE 4.

Final multivariable model for the likelihood of isolating Listeria spp. and L. monocytogenes from spinach fields based on testing of soil samples and given a P value cutoff of 0.05

Factor	ORa	95% CIb	P value
Factors significant for Listeria spp.c
Amt of irrigation water (mm) applied to fields 2 days before sample collection	1.1	1.0, 1.2	0.04
Event type that initiated sample collection
Irrigation	0.71	0.40, 1.2	0.22
Rain	1.0
Time since event occurred (h)
24	7.7	2.9, 20	<0.01
48	2.1	0.74, 6.2	0.16
72	2.5	0.94, 6.9	0.07
144–192	1.0
Predicted field risk
Low	1.0
High	2.3	1.5, 3.5	<0.01
Total amt of rain (mm) on day 2 before sample collection	1.4	1.1, 1.8	<0.01
Factors significant for L. monocytogenes
Amt of irrigation water applied to fields 2 days before sample collection	1.2	1.1, 1.3	<0.01
Event type that initiated sample collection
Irrigation	0.74	0.41, 1.3	0.33
Rain	1.0
Time (h) since event occurred
24	25	5.7, 99	<0.01
48	2.5	0.49, 12	0.27
72	3.4	0.74, 15	0.11
144–192	1.0
Predicted field risk
Low	1.0
High	3.5	2.0, 6.0	<0.01

^aFor continuous factors, OR refers to the change in the odds of isolating Listeria spp. or L. monocytogenes associated with a one-unit increase in the factor (e.g., a 1-mm increase in the amount of irrigation water applied).

^bCI, confidence interval for the odds ratio.

^cListeria spp. including L. monocytogenes.