Table 6. ORs for the most important determinants of livestock-associated MRSA positivity in 1,054 pooled pig samples from 32 farms (multivariable final model), the Netherlands, 2011–2013*.

Characteristic	No.†	OR (95% CI)	p value
Sampling time
0 mo	262	0.83 (0.48–1.43)	<0.001
6 mo	290	2.05 (1.25–3.37)
12 mo	259	1.96 (1.20–3.20)
18 mo	243	Ref
Age group
Gilts	212	1.08 (0.65–1.80)	<0.001
Finishers	140	4.09 (2.30–7.25)
Suckling piglets	212	3.87 (2.34–6.39)
Weaned piglets	280	9.89 (5.96–16.39)
Sows	210	Ref
External supply of gilts‡
Open	630	5.54 (1.56–19.27)	0.008
Closed	424	Ref
Delivery room for materials
Yes	804	0.29 (0.13–0.62)	0.001
No	250	Ref
Sows housed in stable groups
Yes	594	0.53 (0.29–0.96)	0.038
No	460	Ref
Antimicrobial drug use, per 2-fold increase, log2 DDDA/Y	1,054	1.22 (1.03–1.44)	0.024
Use of cephalosporins
Yes	84	3.15 (1.47–6.74)	0.003
No	970	Ref

*Model fit: −2 log RSPL estimation = 5331.7. Multivariable final model after backward elimination of non-significant variables from a full model (online Technical Appendix Table 3, http://wwwnc.cdc.gov/EID/article/21/6/14-0706-Techapp1.pdf) containing the significant associations (p<0.05) presented in Table 5 (http://wwwnc.cdc.gov/EID/article/21/6/14-0706-T5.htm) for all farms, together with antimicrobial drug use, use of cephalosporins, sampling time, and age group of the pool. MRSA, methicillin-resistant Staphylococcus aureus; OR, odds ratio; DDDA/Y, defined daily dosages animal per year; Ref, reference category; RSPL, residual pseudo-likelihood.
†Multiple variables had missing values in the full model reducing the number of observations in the final model.
‡Farms were defined as open when they received external supplies of gilts ≥1 time per year from at least 1 supplier and as closed when they received no external supply of gilts.