Table 6.

Climatic associations with E. coli O157 shedding in a cohort of 52 dairy heifers, estimated by bivariate logistic regression. Levels are the number of days the arbitrary threshold was reached in the 7 days prior to sampling with the exception of temperature (T), which was counted over 14 days prior to sampling

Parameter	n	Estimate	s.e.	95% CI	P	OR
RH <90%	529	−0·481	0·089	−0·657 to −0·306	n.a.	1
RH ⩾90%, 1 day	261	0·489	0·153	0·19 to 0·789	0·001	1·631
RH ⩾90%, 2 days	52	3·274	0·593	2·112 to 4·437	<0·001	26·43
T < 37°C	496	−0·563	0·093	−0·745 to 0·38	n.a.	1
T ⩾37°C, 1 day	100	1·138	0·228	0·692 to 1·584	<0·001	3·121
T ⩾37°C, 2 days	49	1·381	0·323	0·748 to 2·014	<0·001	3·979
T ⩾37°C, 3 days	96	0·646	0·225	0·206 to 1·086	0·004	1·908
T⩾37°C, 4 days	52	1·285	0·309	0·679 to 1·891	<0·001	3·614
T ⩾37°C, 5 days	49	0·106	0·307	−0·496 to 0·709	0·73	1·112
No rain	190	−0·584	0·151	−0·881 to 0·288	n.a.	1
Rain ⩾0·1 mm, 1 day	196	−0·093	0·213	−0·512 to 0·325	0·662	0·911
Rain ⩾0·1 mm, 2 days	88	0·905	0·263	−0·389 to 1·421	<0·001	2·473
Rain ⩾0·1 mm, 3 days	166	−0·011	0·221	−0·445 to 0·423	0·961	0·989
Rain ⩾0·1 mm, 4 days	151	1·71	0·242	1·236 to 2·184	<0·001	5·528
Rain ⩾0·1 mm, 5 days	51	0·467	0·319	−0·158 to 1·091	0·143	1·595
SE <20 mJ/m2	103	0·175	0·198	−0·212 to 0·563	n.a.	1
SE ⩾20 mJ/m2, 3 days	123	0·555	0·275	0·015 to 1·095	0·044	1·741
SE ⩾20 mJ/m2, 4 days	49	−0·632	0·353	−1·325 to 0·061	0·074	0·532
SE ⩾20 mJ/m2, 5 days	241	−0·283	0·236	−0·746 to 0·179	0·23	0·753
SE ⩾20 mJ/m2, 6 days	235	−0·972	0·243	−1·448 to −0·497	<0·001	0·378
SE ⩾20 mJ/m2, 7 days	91	−0·553	0·291	−1·123 to 0·017	0·057	0·575

s.e. Standard error; CI, confidence interval; OR, odds ratio; n.a., not applicable as the reference level; RH, relative humidity; SE, solar exposure.