Prevalence and Risk Factors for the Contamination of Cattle Carcasses With Shiga Toxin-Producing Escherichia coli in Provincially Licensed Abattoirs in Ontario, Canada, Based on Molecular Surveillance

Abstract

Introduction

Reducing the prevalence of Shiga toxin-producing Escherichia coli (STEC) is an important responsibility of provincial abattoirs to ensure safe products are entering the human food chain. Currently, within Ontario, provincial abattoirs are mandated to apply various antimicrobial treatments to cattle carcasses to help decrease pathogen presence post-slaughter. The objectives of this study were to determine the prevalence of contamination of O157 and non-O157 STEC in carcasses from Ontario provincial abattoirs.

Methods

Using mixed logistic regression models, we examined the associations between cattle characteristics, season, monitoring program and abattoir interventions on carcass contamination with E. coli O157:H7, non-O157:H7 STEC and the top six non-O157:H7 STEC of concern to public health (i.e., O26, O45, O103, O111, O121 and O145). Random effects for abattoir and the area in which an abattoir was located were included in these models to adjust for clustering at these levels. The STEC examined was detected through two provincial molecular-based monitoring programs.

Results

Samples taken in the summer had significantly greater odds of screening positive for the top six STEC compared to samples taken in the fall and winter months. Similar seasonal effects were observed for E. coli O157:H7, but for only one of the monitoring programs (i.e., seasonal effects were modified by a monitoring program). Carcasses that received dry age treatment had significantly lower odds of screening positive for STEC. Samples collected from veal calf and cow carcasses had significantly greater odds of screening positive for STEC than samples taken from the carcasses of steers or heifers, but not bulls. Most of the variance in carcass contamination was explained at the carcass level.

Conclusions

These results suggest that additional efforts in risk mitigation should focus on cattle of certain demographic characteristics and higher risk seasons and that additional carcass-level interventions be explored.