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Volume 21, Number 6—June 2015

Dose-Response Relationship between Antimicrobial Drugs and Livestock-Associated MRSA in Pig Farming1

Alejandro Dorado-GarcíaComments to Author , Wietske Dohmen, Marian E.H. Bos, Koen M. Verstappen, Manon Houben, Jaap A. Wagenaar, and Dick J.J. Heederik
Author affiliations: Utrecht University, Utrecht, the Netherlands (A. Dorado-García, W. Dohmen, M.E.H. Bos, K.M. Verstappen, J.A. Wagenaar, D.J.J. Heederik); Wageningen UR, Lelystad, the Netherlands (J.A. Wagenaar); PorQ BV, Son, the Netherlands (M. Houben).

Main Article

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

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)

External supply of gilts‡
Open 630 5.54 (1.56–19.27) 0.008

Delivery room for materials
Yes 804 0.29 (0.13–0.62) 0.001

Sows housed in stable groups
Yes 594 0.53 (0.29–0.96) 0.038

Antimicrobial drug use, per 2-fold increase, log2 DDDA/Y
1.22 (1.03–1.44)
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, containing the significant associations (p<0.05) presented in Table 5 ( 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.

Main Article

1Preliminary results from this study were presented at the 3rd American Society for Microbiology–European Society of Clinical Microbiology and Infectious Diseases (ASM-ESCMID) Conference on Methicillin-resistant Staphylococci in Animals: Veterinary Public Health Implications, 2013 November 4–7, Copenhagen, Denmark (oral presentation, speaker abstract S7:3); and at the Society for Veterinary Epidemiology and Preventive Medicine annual meeting, 2014 March 26–28, Dublin, Ireland (poster presentation).

Page created: May 15, 2015
Page updated: May 15, 2015
Page reviewed: May 15, 2015
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