TABLE 3.

Multivariable risk factor analysis, assessing for the association between genotypic multi-drug resistance and variables of interest (n = 492, of which 296 were multi-drug resistant).

Variable	Level	No. isolates	Odds ratio	P-value	95% confidence intervals
Antimicrobial usage	Low	72	Baseline
	Medium	116	2.84	0.050	1.00	8.08
	High	151	7.64	<0.001	2.73	21.35
Antibiotic selective or non-selective plate#	1 mg/L CIP	197	Baseline
	1 mg/L CTX	37	0.15	<0.001	0.06	0.40
	CRE*	4	Undefined	0.985	–	–
	No antibiotic	254	0.03	<0.001	0.02	0.07
Production type	Breeder-finisher	339	Baseline
	Finisher only	153	3.69	<0.001	1.79	7.58
How often is manure pit emptied	Weekly	65	Baseline
	Monthly	108	2.09	0.114	0.84	5.20
	Per batch	123	3.57	0.023	1.20	10.65
	Half yearly	8	0.46	0.513	0.05	4.67
Region of farm	South West	137	Baseline
	South East	63	3.65	0.012	1.32	10.07
	East of England	65	0.60	0.251	0.25	1.44
	Midlands	91	1.11	0.821	0.44	2.85
	Yorkshire and Humber	97	0.42	0.038	0.19	0.95
	North East	39	1.66	0.381	0.53	5.15
On average, how often are pens cleaned and disinfected	Always, sometimes or between batches	413	Baseline
	Never	43	0.27	0.012	0.10	0.75
	Missing	36	1.24	0.708	0.40	3.80

Variable levels for ‘not known’ or missing answers have been omitted from the table. *Small study population led to large uncertainty for odds ratio. ^#CRE, carbapenem-resistant Enterobacteriaceae; CIP, ciprofloxacin; CTX, cefotaxime.