9/11/2020: Sampling 1 9/25/2020: Sampling 2 10/2/2020: Sampling 3 10/23/2020: Sampling 4 10/30/2020: Sampling 5 9/16/2020: 10/21/2020: Increased frequency of cleaning and sanitation to twice a week. Weekly quaternary ammonium compound (quat) powder application around forklift stops Figure 1. 10/26/2020: Weekly quat powder application around the floor crack 10/28/2020: Removal of deadend from pipe Deep cleaning of drains FIGURE 1. Sampling events and intervention implementation timeline for eliminating Listeria in the apple packinghouse. The root cause analysis for intervention identification was performed on October 25th, 2019. i. Company Practices/ Food Safety Culture 1.1 Education and training 1.2 Resources provided to employees 1.3 Routes for employee feedback 1.4 Enforcement of cGMPs 1.5 Verification and validation procedures 1.6 Importance of food safety to the company iii. Facilities 3.1 Overall building structure 3.2 Floor and walls 3.3 Drains 3.4 Employee areas 3.5 Restrooms 3.6 Maintenance facilities and equipment 3.7 Environmental conditions 3.8 Hygienic zoning of facility 2.6 Line workers 2.5 Cleaning and sanitation team 2.3 Maintenance personnel 2.4 Processing/ 2.2 Food safety and quality personnel 4.1 Procedures 2.1 Management ii. Personnel engineering personnel 4.2 Schedules 4.4 Training and education 4.3 Equipment and materials 5.2 Pre-harvest conditions v. Produce Introduction 5.1 Bins for the storage or transfer of produce vii. Produce Processing Equipment 7.1 Chopping, cooking, cutting, homogenization, irradiation, and/ or pasteurization 7.2 Assembly 5.3 Amount of organic material on produce 5.4 Previous storage conditions 7.3 Refrigeration or freezing 7.4 Packaging 7.5 Shipping 6.4 Brush beds 6.5 Drying 6.6 Waxing 6.7 Packaging 6.8 Shipping 6.1 Preliminary washing 6.2 Sorting and culling 6.3 Cleaning and sanitation of produce Persistent Listeria iv. Cleaning and Sanitation vi. Packinghouse equipment FIGURE 2. Fishbone diagram utilized in root cause analysis to identify interventions to eliminate Listeria in Figure 2. the packinghouse environment. This fishbone diagram was adapted from: Belias, A. and M. Wiedmann. 2021. Hazards, risks, and challenges of Listeria in the food supply. Food Safety Management in Practice. In press. 2 November/December Food Protection Trends 557