Herd-level risk factors associated with the presence of Phage type 21/28 E. coli O157 on Scottish cattle farms

BMC Microbiology BioMed Central Research article Open Access Herd-level risk factors associated with the presence of Phage type 21/28 E. coli O157 on Scottish cattle farms Jo EB Halliday*1, Margo E Chase-Topping2, Michael C Pearce3, Iain J McKendrick4, Lesley Allison5, Dave Fenlon3, Chris Low3, Dominic J Mellor6, George J Gunn3 and Mark EJ Woolhouse2 Address: 1Centre for Infectious Diseases, University of Edinburgh, Easter Bush, Roslin, Midlothian, EH25 9RG, UK, 2Centre for Infectious Diseases, University of Edinburgh, Ashworth Laboratories, King's Buildings, West Mains Road, Edinburgh, EH9 3JF, UK, 3Scottish Agricultural College, Animal Health Group, Research Division, King's Buildings, West Mains Road, Edinburgh, EH9 3JG, UK, 4Biomathematics & Statistics Scotland, King's Buildings, West Mains Road, Edinburgh, EH9 3JZ, UK, 5Scottish E. coli O157 Reference Laboratory, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU, UK and 6Comparative Epidemiology & Informatics, Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow, G61 1QH, UK Email: Jo EB Halliday* - ; Margo E Chase-Topping - ; Michael C Pearce - ; Iain J McKendrick - ; Lesley Allison - ; Dave Fenlon - ; Chris Low - ; Dominic J Mellor - ; George J Gunn - ; Mark EJ Woolhouse - * Corresponding author Published: 02 December 2006 BMC Microbiology 2006, 6:99 doi:10.1186/1471-2180-6-99 Received: 22 May 2006 Accepted: 02 December 2006 This article is available from: http://www.biomedcentral.com/1471-2180/6/99 © 2006 Halliday et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: E. coli O157 is a bacterial pathogen that is shed by cattle and can cause severe disease in humans. Phage type (PT) 21/28 is a subtype of E. coli O157 that is found across Scotland and is associated with particularly severe human morbidity. Methods: A cross-sectional survey of Scottish cattle farms was conducted in the period Feb 2002-Feb 2004 to determine the prevalence of E. coli O157 in cattle herds. Data from 88 farms on which E. coli O157 was present were analysed using generalised linear mixed models to identify risk factors for the presence of PT 21/28 specifically. Results: The analysis identified private water supply, and northerly farm location as risk factors for PT 21/28 presence. There was a significant association between the presence of PT 21/28 and an increased number of E. coli O157 positive pat samples from a farm, and PT 21/28 was significantly associated with larger E. coli O157 counts than non-PT 21/28 E. coli O157. Conclusion: PT 21/28 has significant risk factors that distinguish it from other phage types of E. coli O157. This finding has implications for the control of E. coli O157 as a whole and suggests that control could be tailored to target the locally dominant PT. Page 1 of 5 (page number not for citation purposes) BMC Microbiology 2006, 6:99 Background Escherichia coli (E. coli) O157 is a bacterial pathogen capable of causing potentially fatal gastrointestinal disease in humans. In 2004 there were a total of 918 laboratory confirmed infections in the UK [1,2]. 209 of these cases occurred in Scotland where the rate of infections per hundred thousand is consistently higher than in the rest of the UK[1]. E. coli O157 is shed by cattle, which are believed to be a major reservoir for human infections. Phage type (PT) 21/28 is a subtype of E. coli O157 that was first detected in Scotland in 1994 [3]. By 2003 this PT dominated Scottish clinical cases, accounting for roughly two thirds of human isolates [4]. PT 21/28 is of particular concern because of its association with severe morbidity. Haemolytic uraemic syndrome (HUS) is a potentially fatal complication of E. coli O157 infection. A recent survey of HUS cases in the UK and Ireland indicated that the risk of developing diarrhoea-associated HUS was significantly higher in children in Scotland infected with PT 21/ 28 than with the majority of other PTs [5]. The aims of this study were to use data collected during a survey of Scottish cattle farms to estimate the prevalence of PT 21/28, to investigate the association between PT and the count of E. coli O157 in faecal pats, and to identify risk factors for the presence of PT 21/28 at the farm level relative to other PTs. Methods Study Group and Sampling Protocol The study group comprised 88 Scottish cattle farms on which the presence of E. coli O157 was identified during a larger cross-sectional survey of 481 farms conducted from February 2002 to February 2004. The 481 study farms were stratified into 6 regions, corresponding to the six Scottish animal health divisions recognised by the Scottish Executive Environment and Rural Affairs Department (SEERAD). Within each region, farms were sampled throughout the 2 year period in clusters of three. The principal farm in each cluster was selected at random and a list of the six farms nearest to it but within the same region was drawn up. Following consent to visit the principal farm, farms on the list of six were approached sequentially to identify a sampling cluster of three participating farms. Farms in the same cluster were visited on the same or contiguous days. On each farm, groups of store and finishing cattle were identified and sampled. The number of faecal pats sampled in each group was determined from the number of cattle in the group using a prescribed sampling schedule. For each group, sufficient pat samples were taken to ensure 90% probability of detecting shedding of E. coli O157 if on average 8% of animals were shedding in positive groups, with shedding distributed as seen in an earlier study commissioned by the Scottish Executive Environment and Rural Affairs Department. Faecal sam- http://www.biomedcentral.com/1471-2180/6/99 ples were refrigerated at 5°C. The majority were refrigerated within two hours of sampling, while a small number were held at ambient temperature before refrigeration on the day after sample collection. Laboratory Analysis Within 48 hours faecal samples were examined by immunomagnetic separation (IMS) to detect the presence of E. coli O157 as described by Pearce et al., 2004 [6]. To estimate E. coli O157 counts, 1 g of faeces from each E. coli O157 positive sample was suspended in 9 ml of maximum recovery diluent (Oxoid Ltd, Basingstoke, UK) and 0.1 ml of suspension spread onto each of two CT-SMAC plates. Plates were incubated at 42°C for 24 hours. Typical non-sorbitol fermenting colonies were counted and tested using anti-E. coli O157 coated latex reagent (Oxoid Ltd.). The limit of accurate enumeration using this method was 100 colony forming units (CFU)g-1 faeces [7]. One E. coli O157 is (...truncated)