TABLE 3.

Multivariate analysis of risk factors for isolation of E. coli^a

Ampicillin-sulbactam-resistant E. coli			Ampicillin-sulbactam-susceptible E. coli
Variable	P value	OR (95% confidence interval)	Variable	P value	OR (95% confidence interval)
Exposure to all penicillins	<0.001	2.32 (1.54–3.51)	Quinolone exposure	<0.001	0.22 (0.11–0.46)
Ampicillinb	0.02	3.04 (1.22–7.58)
Ampicillin-sulbactamb	0.04	1.72 (1.03–2.85)
Piperacillinb	0.15	2.55 (0.71–9.25)
Piperacillin-tazobactamb	0.11	0.13 (0.01–1.60)
ICU stay	<0.001	2.47 (1.64–3.72)	ICU stay	<0.001	2.89 (2.19–3.82)
Cefazolin exposure	<0.001	0.35 (0.20–0.59)	Cefazolin exposure	<0.001	0.43 (0.31–0.60)
Gender (female)			Gender (female)	<0.001	3.14 (2.47–4.00)
Surgical patientsc	0.20	1.46 (0.82–2.61)
Nonsurgical patientsd	<0.001	5.14 (3.14–8.43)
Surgery			Surgery	<0.001	1.73 (1.30–2.32)
Malee	<0.001	3.96 (2.17–7.24)
Femalef	0.67	1.13 (0.65–1.94)
			Ageg	<0.001	1.03 (1.02–1.04)
			Transfer	0.008	1.42 (1.09–1.84)
			Hepatic disease	<0.001	2.26 (1.50–3.39)
			Cardiac disease	0.02	0.68 (0.51–0.92)

^aThis table shows two multivariate models. Variables were selected by a forward selection process, and confounding variables were added back to the models. Several associations that were significantly associated with the recovery of E. coli by univariate analysis were no longer statistically significant by multivariate analysis, and thus were not selected for use in the final model. For the ampicillin-sulbactam-resistant E. coli model, penicillin antibiotics as a class were selected. In order to study the relationships among the individual penicillin antibiotics and the isolation of ampicillin-sulbactam-resistant E. coli, the penicillin class was removed, and each individual penicillin antibiotic was studied in the model individually. Boldface type indicates variables for which P is <0.05. 

^bOR and P value when penicillin class is removed from the model. 

^cEffect of female gender in surgical patients. 

^dEffect of female gender in nonsurgical patients. 

^eEffect of surgery in male patients. 

^fEffect of surgery in female patients. 

^gRisk is per year.