Root Cause Analysis Can be Used to Identify  and Reduce a Highly Diverse Listeria Population in an Apple Packinghouse: A Case Study

Root cause analysis (RCA) was utilized to identify Listeria elimination strategies in an apple packinghouse. While most of the Listeria was not persistent according to sigB allelic typing (i.e.,16 allelic types were isolated from 22 positive samples), the same packinghouse sites were continually positive. The root cause was identified as a limited understanding of how to eliminate Listeria. Based on these findings, we provided instructions on proper Listeria elimination strategies and supported implementation, including (i) increasing cleaning and sanitation from once to twice a week, (ii) use of quaternary ammonium compound (quat) powder around forklift stops and floor cracks, and (iii) removal of a dead-end pipe. Five samplings were conducted to test intervention effectiveness. While increased cleaning and sanitation frequency did not significantly reduce the log-odds of a site testing Listeria positive [11% (4/35) before and 13% (18/137) after, P = 0.787 by logistic regression], the site-specific interventions appeared to have controlled the Listeria at the respective sites. Specifically, after utilizing quat powder, Listeria was not isolated from the forklift stops or floor crack (0/5 samples positive after versus 6/10 samples positive before intervention). Therefore, this study provides a roadmap for performing RCA and implementing interventions for controlling Listeria in packinghouses.