Risk Factors for the Presence of High-Level Shedders ofEscherichia coliO157 on Scottish Farms

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Abstract
Escherichia coliO157 infections are the cause of sporadic or epidemic cases of often bloody diarrhea that can progress to hemolytic uremic syndrome (HUS), a systematic microvascular syndrome with predominately renal and neurological complications. HUS is responsible for most deaths associated withE. coliO157 infection. From March 2002 to February 2004, approximately 13,000 fecal pat samples from 481 farms with finishing/store cattle throughout Scotland were examined for the presence ofE. coliO157. A total of 441 fecal pats from 91 farms tested positive forE. coliO157. From the positive samples, a point estimate for high-level shedders was identified using mixture distribution analysis on counts ofE. coliO157. Models were developed based on the confidence interval surrounding this point estimate (high-level shedder, greater than 103or greater than 104CFU g−1feces). The mean prevalence on high-level-shedding farms was higher than that 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 a higher level of 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 of 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.

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