TABLE 2.

Frequency and prevalence of Listeria spp. and L monocytogenes in soil samples collected 24, 48, 72, and 144 to 192 h after irrigation and rain events from two spinach fields previously identified as being at high or low risk for L. monocytogenes isolation

Event typea	Time (h)b (no. of samples)	No. (%) of samples positive for:
		Listeria spp.c	L. monocytogenes
Low-risk field
Presample	NA (21)	1 (5)	1 (5)
Irrigation	24 (42)	8 (19)	7 (17)
	48 (42)	3 (7)	2 (5)
	72 (42)	2 (5)	2 (5)
	144–192 (21)	0 (0)	0 (0)
Rain	24 (105)	16 (15)	7 (7)
	48 (105)	7 (7)	2 (3)
	72 (105)	4 (4)	2 (3)
	144–192 (63)	2 (3)	1 (1)
High-risk field
Presample	NA (21)	4 (19)	2 (10)
Irrigation	24 (42)	11 (26)	10 (24)
	48 (42)	11 (26)	11 (26)
	72 (42)	5 (12)	2 (5)
	144–192 (21)	0 (0)	0 (0)
Rain	24 (105)	33 (31)	28 (27)
	48 (105)	7 (7)	3 (3)
	72 (105)	3 (3)	5 (12)
	144–192 (63)	3 (5)	1 (16)

^aEvent type (i.e., irrigation or rain event) that initiated sample collection.

^bTime in hours (i.e., 24, 48, 72, or 144 to 192 h) since the event. NA (not applicable) indicates that samples were collected before study initiation.

^cListeria spp. including L. monocytogenes.