Risk factors associated with the A2C resistance pattern among E. coli isolates from broiler flocks in Canada

The extra-label use of ceftiofur in Canadian hatcheries was cause for concern due to an increased prevalence of ceftiofur resistant Salmonella Heidelberg in chickens and humans in Québec. Due to on-going concerns related to human health the use of ceftiofur was eventually phased out of the poultry production industry in 2014-2015. Simultaneous resistance to amoxicillin-clavulanic acid, ceftiofur and cefoxitin, a pattern known as A2C, caused by the presence of bla_CMY-2 has become increasingly prevalent in broiler flocks worldwide. This study used data from the Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS) broiler farm surveillance program to examine the risk factors for A2C resistant Escherichia coli isolates (A2C-REI) from 1482 samples taken from 371 broiler flocks in Canada, between 2013 and 2015. Results of a mixed effects Poisson model with fixed effects at the flock level and random effects at the hatchery level indicated that the in ovo use of ceftiofur (Prevalence Ratio (PR): 1.91, 95% CI: 1.43-2.57), and the use of hydrogen peroxide to disinfect water lines during the growing period (PR: 1.52, 95% CI: 1.11-2.07), were risk factors for increased expected prevalence of A2C-REI, compared to farms not using these strategies. Controlling for wild birds (PR: 0.64, 95% CI: 0.48-0.84), use of avilamycin in feed (PR: 0.63, 95% CI: 0.41-0.98), and storage of manure on the farm (PR: 0.67, 95% CI: 0.51-0.89) were associated with a lower expected prevalence of A2C-REI, than farms that did not use these strategies. This study identified important management factors that were associated with the prevalence of A2C-REI on Canadian broiler farms. The findings of this study can be used as a baseline for the monitoring of the effects of the removal of ceftiofur from poultry production in Canada.