A Summary Index for Antimicrobial Resistance in Food Animals in The Netherlands

Introduction: The Dutch government has set targets for reduction of antimicrobial usage in food animals, stipulating a 50% reduction in usage (on a weight basis) in 2013 as compared to 2009 and a 70% decrease in 2015. To evaluate the impact of this policy for public health, antimicrobial resistance (AMR) is monitored for several pathogenic and commensal bacteria (including E. coli and Enterococcus spp.) in food animals as well as foods.

Purpose: A summary index of AMR in the food chain is needed, in order to comprehensively report the impact of reducing antimicrobial usage in food animals on AMR in food-related isolates to parliament.

Methods: Scientists and policy makers contributed to the definition of a set of criteria to evaluate existing monitoring systems and relevant antimicrobial agents. Data on AMR in selected isolates from four animal species (broiler chickens, pigs, veal calves and dairy cattle) were obtained from 2009-2012. Different methods of aggregating these data were explored.

Results: Monitoring for resistance in commensal Escherichia coli best met the required characteristics. Antimicrobial classes selected for inclusion in the summary index were therapeutically important substances (3^rd/4^thgeneration cephalosporins and quinolones) and high usage substances (tetracyclines and penicillins). Resistance to critically important antimicrobials was less prevalent than to high usage antimicrobials. The mean trend anchored to the average resistance level in 2009 was preferred by policy makers.

Significance: Reducing AMR in food animals is a key policy objective in many countries around the world. This study shows that active monitoring of resistance among commensal bacteria can inform about the impact of such policies, and that detailed data can be aggregated to summary indices that are meaningful for policy makers.