TABLE 5.

Two separate cumulative logistic regression GEE models assessing the influence of prior antimicrobial treatment, sampling time, and trial group affiliation on increasing multiple resistance of fecal E. coli

Variable	N	Estimate	P value	Odds ratiob	95% C.I.a
No antibiotic in milk replacer (groups 1 to 3; N = 646)
Antimicrobial therapy within 5 days of sampling
None	592	Reference
Treated	54	1.11	0.02	3.03	1.15-7.98
Study group
1	196	Reference
2	213	−0.05	0.87	0.95	0.56-1.65
3	237	0.23	0.43	1.26	0.71-2.25
Calf age at sampling
1 day	241	Reference
14 days	222	2.32	<0.001	10.18	5.69-18.3
28 days	183	1.64	<0.001	5.16	2.82-9.41
Antibiotic in milk replacer (group 4; N = 263)
Antimicrobial therapy within 5 days of sampling
None	248	Reference
Treated	15	−0.67	0.13	0.51	0.21-1.24
Calf age at sampling
1 day	92	Reference
14 days	90	6.41	<0.001	608.5	186.27-1,989.03
28 days	81	6.47	<0.001	645.87	196.25-2,125.79

^aC.I., confidence interval.

^bCumulative odds ratio for increasing levels of resistance.