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J. Clin. Microbiol. doi:10.1128/JCM.01690-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Risk factors for the presence of high-level shedders of Escherichia coli O157 on Scottish farms

Centre for Infectious Diseases, University of Edinburgh, King's Buildings, Edinburgh, UK; Biomathematics & Statistics Scotland, University of Edinburgh, King's Buildings, Edinburgh, UK; Scottish Agricultural College, Animal Health Group, Research Division, King's Buildings, Edinburgh, UK; Department of Mathematics & Statistics, McMaster University, Ontario, Canada; Institute for Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Glasgow, UK; Centre for Tropical Veterinary Medicine, Easter Bush, Roslin, Midlothian, UK; Scottish E. coli O157 Reference Laboratory, Western General Hospital, Edinburgh, UK

^* To whom correspondence should be addressed. Email: margo.chase{at}ed.ac.uk.

	Abstract

Escherichia coli O157 infections are the cause of sporadic or epidemic cases of often bloody diarrhoea, that can progress to haemolytic uraemic syndrome (HUS), a systematic microvascular syndrome, with predominately renal and neurological complications. HUS is responsible for most deaths associated with E. coli O157 infection. From March 2002 to February 2004, approximately 13,000 faecal pat samples from 481 farms with finishing/store cattle throughout Scotland were examined for the presence of E. coli O157. A total of 441 faecal pats from 91 farms tested positive for E. coli O157. From the positive samples, a point estimate for high-level shedders was identified using mixture distribution analysis on counts of E. coli O157. Models were developed based on the confidence interval surrounding this point estimate (high-level shedder: greater than 10³ or greater than 10⁴ C.F.U. g^-1 faeces). Mean prevalence on high-level shedding farms was higher than on low-level shedding farms. The presence of a high-level shedder on a farm was found to be associated with a high proportion of low level shedding, consistent with the possibility of higher transmission. Analysis of risk factors associated with the presence of a high-level shedder on a farm suggested the importance of the pathogen and individual host rather than the farm environment. The proportion of high-level shedders that were phage 21/28 was higher than expected by chance. Management-related risk factors that were identified included the type of cattle (female breeding cattle) and cattle stress (movement and weaning) as opposed to environmental factors such as water supply and feed.