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Applied and Environmental Microbiology, October 2008, p. 6313-6319, Vol. 74, No. 20
0099-2240/08/$08.00+0     doi:10.1128/AEM.00770-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Factors Associated with Cross-Contamination of Hides of Scottish Cattle by Escherichia coli O157

A. E. Mather,^1, S. W. J. Reid,² S. A. McEwen,¹ H. E. Ternent,² R. J. Reid-Smith,^1,3 P. Boerlin,^3,4 D. J. Taylor,² W. B. Steele,² G. J. Gunn,⁵ and D. J. Mellor^2,6*

Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Canada,¹ Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Glasgow, United Kingdom,² Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, Guelph, Canada,³ Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Canada,⁴ Scottish Agricultural College, Research Division, Kings Buildings, Edinburgh, United Kingdom,⁵ Health Protection Scotland, Glasgow, United Kingdom⁶

Received 3 April 2008/ Accepted 11 August 2008

The putative source of hide contamination for 236 cattle in Scotland followed from the farm through to slaughter was determined using phage and verocytotoxin type data. The majority of cattle (84%) were found to have subtypes of Escherichia coli O157 on their hide that had not been found previously in any animal from the farm of origin, strongly suggesting that contamination occurred once animals had left the farm of origin. Using logistic regression analysis, several variables and factors were found to be strongly associated (P < 0.01) with cross-contamination of cattle hides at the univariate level; commercial transport to slaughter, transport with other animals, use of a crush, line automation, and increasing slaughterhouse throughput were all risk factors, while feeding hay in lairage, processing an animal earlier in a slaughter cohort, and cleaning the landing area poststunning were protective. In the multivariable model, with the slaughterhouse and the farm group included as random effects, factors associated with the cross-contamination of cattle hides were identified. Transport to the slaughterhouse by a commercial hauler had a borderline-significant association with increased odds of an animal having a cross-contaminated hide (odds ratio [OR] [95% confidence interval {CI}] = 5.7 [0.99, 33.0]; P = 0.05). At the slaughterhouse, providing hay to cattle waiting in lairage (OR [95% CI] = 0.04 [<0.01, 1.04]; P = 0.05) and cleaning the landing area (OR [95% CI] = 0.03 [<0.01, 1.15,]; P = 0.06) also had a borderline-significant association with decreased odds of an animal having a cross-contaminated hide. Although the prevalence of carcass contamination remains very low, targeted intervention at the preslaughter stage may have the potential to reduce further the risk to public health.

Published ahead of print on 22 August 2008.

Present address: Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Glasgow, United Kingdom.