A diagnostic strategy to determine the Shiga toxin-producing Escherichia coli O157 status of pens of feedlot cattle

Although cattle are reservoirs, no validated method exists to monitor Shiga toxin-producing Escherichia coli O157 (STEC O157) on farms. In 29 Midwestern United States feedlot pens we compared culturing faeces from the individual cattle to: (1) culturing rope devices that cattle rub or chew; and (2) culturing a composite of faecal pats. Eighty-six per cent (68-96 %) of pens were classified correctly using rope devices to detect pens with at least 16 % of the cattle shedding STEC O157 [sensitivity = 82 % (57-96 %); specificity = 92 % (62-100 %)]. Ninety per cent of pens (73-98 %) were classified correctly using composite faeces to detect pens with at least 37 % of the cattle shedding STEC O157 [sensitivity = 86 % (42-100 %); specificity = 91 % (71-99 %)]. Ranking pens into three risk levels based on parallel interpretation of the pen-test results correlated (Spearman's r=0.76, P<0.0001) with the pen's prevalence. This strategy could identify pens of cattle posing a higher risk to food safety.