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Volume 21, Number 6—June 2015
Research

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 5

ORs for determinants of livestock-associated MRSA positivity in pooled samples from pigs, the Netherlands, 2011–2013*

Characteristic
 All farms
Open farms
Closed farms
No.†
 OR (95% CI)
No.†
 OR (95% CI)
No.†
 OR (95% CI)
Farm
No. sows, 300 increase§ 1,421 1.4 (0.7–2.7) 867 1.3 (0.8–2.2) 554 2.6 (0.7–9.7)
External supply of gilts
Open 867 6.6 (2.3–19.0) 867 Not computable 0 Not computable
Closed 554 Ref 0 554
Type of production
Farrow-to-finish 945 0.4 (0.1–1.6) 511 0.7 (0.3–1.6) 434 0.4 (0.0–17.7)
Farrowing 476 Ref 356 Ref 120 Ref
Farm treatment plan
Yes 1,157 0.7 (0.4–1.3) 723 0.6 (0.3–1.1) 434 2.1 (0.6–7.1)
No 190 Ref 110 Ref 80 Ref
Water supply for animals
Public, from tap 452 2.8 (1.3–6.0)# 218 0.8 (0.4–1.8) 234 7.7 (2.5–24)#
Private from private source 929 Ref 619 Ref 310 Ref
Separate medication pipe
Yes 920 0.4 (0.2–0.7)# 526 0.4 (0.2–0.7)# 394 0.8 (0.2–3.7)
No
 441
 –
311
 Ref
130
 Ref
Biosecurity
Different compartments per production phase
Yes 880 0.9 (0.5–1.6) 600 1.7 (0.8–3.8) 280 0.4 (0.2–1.1)
No 521 Ref 257 Ref 264 Ref
Boarding platform for sows
Yes 512 0.7 (0.4–1.4) 358 1.3 (0.7–2.6) 154 0.2 (0.1–1.0)
No 909 Ref 509 Ref 400 Ref
Clearly defined border of boarding platform
Yes 989 0.7 (0.4–1.3) 569 1.1 (0.6–1.9) 420 0.2 (0.1–0.6)#
No 432 Ref 298 Ref 134 Ref
Carcass barrels cleaned and disinfected after emptied
Yes 527 0.5 (0.3–1.0)** 317 0.4 (0.2–0.8)# 210 1.6 (0.5–5.1)
No 864 Ref 530 Ref 334 Ref
Delivery room for materials
Yes 1,031 0.4 (0.2–0.7)** 677 0.5 (0.2–1.0)** 354 0.3 (0.1–0.6)#
No 320 Ref 140 Ref 180 Ref
Pigs go outside when moved
Yes 627 0.8 (0.4–1.6) 367 1.4 (0.8–2.6) 274 0.2 (0.1–0.8)**
No 744 Ref 470 Ref 260 Ref
Workers’ overalls washed
Yes 687 0.8 (0.5–1.4) 317 1.2 (0.7–2.1) 370 0.3 (0.1–1.2)
No 734 Ref 550 Ref 184 Ref
Removal of manure in winter
Manure stays <6 mo 1,007 1.2 (0.7–2.0) 647 0.8 (0.5–1.5) 360 2.9 (1.0–8.9)
Manure stays >6 mo
 380
 Ref
186
 Ref
194
 Ref
Animal management and contact structure
Injection of piglets with antimicrobial drugs during the first week.
Yes 830 2.0 (1.2–3.3)# 610 1.4 (0.8–2.5) 220 3.7 (1.6–8.6)#
No 571 Ref 257 Ref 314 Ref
Tooth clipping in piglets
Yes 516 3.2 (1.4–7.0)** 34,650 3.0 (1.5–6.2)# 170 4.0 (0.5–30.6)
No 875 Ref 1 Ref 374 Ref
Vaccination of piglets and/or fatteners
Yes 1,090 2.5 (1.4–4.5)** 690 2.0 (1.1–3.4)** 400 7.2 (1.6–32)**
No 311 Ref 167 Ref 144 Ref
Needles for vaccination renewed per compartment
Yes 848 1.9 (1.2–3.1)** 508 1.7 (1.0–2.7)** 340 2.1 (0.4–12.1)
No 456 Ref 312 Ref 144 Ref
Some piglets reared motherless
Yes 385 1.3 (0.7–2.3) 311 1.6 (0.9–2.7) 74 0.2 (0.0–0.9)**
No 1,026 Ref 546 Ref 480 Ref
Sows in stable groups
Yes 772 0.5 (0.3–0.8)# 432 0.6 (0.3–1.0) 340 0.5 (0.2–1.1)
No
 619
 Ref
405
 Ref
214
 Ref
Hygiene
In the piglet section
Disinfectant 189 0.3 (0.2–0.7)# 139 0.3 (0.1–0.7)# 50 0.9 (0.1–5.9)
Soaking agent 280 2.0 (1.0–4.4) 180 3.1 (1.3–7.5)** 100 0.1 (0.0–0.8)**
Disinfectant + soaking agent 698 1.2 (0.6–2.3) 408 1.4 (0.6–3.1) 290 0.8 (0.3–2.5)
None 254 Ref 140 Ref 114 Ref
In the mating section
Disinfectant + soaking agent 239 0.6 (0.3–1.1) 89 0.3 (0.1–0.8)** 150 2.2 (0.6–7.7)
None 1,182 Ref 778 Ref 404 Ref
In the gilt section
Soaking agent 220 1.0 (0.5–2.0) 100 1.5 (0.7–3.6) 120 0.3 (0.1–1.1)
Disinfectant + soaking agent 585 1.0 (0.6–1.6) 335 1.0 (0.6–1.7) 250 1.3 (0.5–3.9)
None 616 Ref 432 Ref 184 Ref

*Fits for the univariate adjusted models in all farms: −2 log RSPL estimations ranged from a minimum of 6386.56 to a maximum of 7016.07. Results from the longitudinal analysis with generalized linear mixed models taking into account the repeated measurements design and adjusted for age group of the pool. Variables with p<0.1 in the overall analysis or in at least 1 stratum (open or closed) are presented. OR and p values are in bold type when p<0.1. 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. MRSA, methicillin-resistant Staphylococcus aureus; OR, odds ratio; Ref, reference category; RSPL, residual pseudo-likelihood.
†Number of observations at all sampling times together (10 pooled pig samples per farm in 36 farms in 4 sampling times). Some variables have missing observations.
§Items evaluated irrespective of significance.
¶p<0.001.
#p<0.01.
**p<0.05.

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).

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