Distribution of Escherichia coli O157 in Bovine Fecal Pats and Its Impact on Estimates of the Prevalence of Fecal Shedding

The density of E. coli O157 in bovine feces was highly variable, differing by as much as 76,800 CFU g 1 between samples from the same fecal pat. The density in most positive samples was <100 CFU g 1 , the limit of reliable detection by IMS. Testing only one 1-g sample of feces per pat with IMS may result in a sensitivity of detection as low as 20 to 50%. It is therefore probable that most surveys have greatly underestimated the prevalence of E. coli O157 shedding in cattle and the proportion of farms with shedding cattle. The sensitivity of the detection of E. coli O157 in bovine feces can be as much as doubled by testing two 1-g samples per pat rather than one 1-g sample. Shiga-toxigenic Escherichia coli O157 is a major public health concern. It is associated with human illnesses ranging from uncomplicated watery diarrhea to hemorrhagic colitis and hemolytic-uremic syndrome, which may result in death