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Régis POUILLOT, DVM, PhD
FDA/CFSAN
Draft - Interagency Listeria monocytogenes in Retail Delicatessens Risk Assessment
Part 1: Design - Data Sources – Modeling Approach
Interagency Risk Assessment - L. monocytogenes in Retail Delicatessens Public Meeting
Transfer coefficients and Slicer– Meta analysis of literature data (In-house study) – Hoelzer K, et al. (2012) International J of Food Microbiology, 157:267-77.
Persistent strains in deli departments– Longitudinal study, Cornell University (FSIS Contract)– Manuscript in preparation
Potential transfer during specific events– Mock deli using GloGerm, Virginia Tech (FSIS Contract)– Maitland J, et al. (2013) J Food Protection, 76 (2): 272-82
Food worker behavior– Observational study (FDA JIFSAN UMD collaboration)– Lubran MB, et al. (2010) J Food Protection, 73 (10):1849-57.
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Lubran MB, et al. (2010) J Food Protection, 73 (10):1849-57
Example #1: Which Sites? Which Events?Observational study in retail environment
Action No.
Action Sequence
1. 10am
Wash hands
2. Put on gloves
3. Open case
4. Pick up salami
5. Close case
6. Put salami on slicer
7. Slice salami on gloves
8. Put salami on tissue
9. Touch scale
10. Give bag to customer
Process Objects Involved
Bacteria inactivation hands
Cross contamination Case - glove
Cross contamination Case - glove
Cross contamination
PartitioningCross contamination
Chub – product sold1st slice – glove
Cross contamination Scale - glove
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Long term data gaps
• Sources of Listeria monocytogenes– Acquired data: frequency of contamination of NFCS– Data needs: better quantification: Relative contribution incoming
food vs. environment?
• Transfer events– Acquired data: better qualifications of NFCS interactions
(drains, sinks,…). – Data needs: better quantification
• Frequency of occurrence of transfers in deli settings• Number of bacteria transferred per transfer.
• Niches– Acquired data: better quantification on the
frequency of occurrence– Data needs: better quantification
• Frequency of transfer to FCS• Number of bacteria transferred
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• Because of the data gaps on the relative impact of environmental contamination vs. contamination from products, we evaluated a range of retail delicatessens conditions
• Approach– Define some baseline conditions
• Baseline #1: regular environmental contaminations occur in the stores
• Baseline #2: no environmental contamination occurs in stores
• …
– Evaluate various scenarios within these baseline conditions
Modeling Approach
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#1: “Multiple Niche 100W” baseline condition• Stores with regular L. monocytogenes transfer from the environment and/or niches• Incoming L. monocytogenes : from incoming products and from the
environment/niche
#2: “No Niche” baseline condition • Stores without transfer from the environment and/or niche• Incoming L. monocytogenes : from incoming products
#3: “Incoming Growth Chub” baseline condition• Stores with highly contaminated incoming product type that supports growth
#4: “Incoming Non-Growth Chub” baseline condition• Stores with highly contaminated incoming product type that does not support growth
#5: “Temperature Control” baseline condition• Stores without transfer from the environment and/or niche and with compliant
temperature control (41°F)
#6: “Niche & Temperature Control” baseline condition• Stores with regular L. monocytogenes transfer from the environment and/or niches
and with compliant temperature control (41°F)
Step 1: Definition of Baseline Conditions
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Step 2: Evaluation of the impact of various mitigation strategies in these contexts
• Within each of the 6 Baseline conditions– 22 Scenarios
• Answer the question (example): – Given that there is a niche in a retail deli, what are the best
mitigation strategies?
and not – What is the probability that there is a niche in the store?
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Approach to Risk Management Questions
• Separate slicers / counters for growth versus non growth products?– Model more than one slicer. Select slicer to use each time
customer is served based on product type.
• What is the impact of the use of “gloves” in the retail environment? – Set probability of wearing gloves to 100%
• Consider frequently touched non-food contact surfaces (e.g. case handles, scale touch pads) as food contact surfaces (i.e., required to be cleaned and sanitized every four hours)?– Change site classification to FCS
Flexibility of the Discrete Event Model
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“What-If” Scenarios
• Sanitation Related Scenarios– Some NFCS cleaned FCS, Increase the effectiveness of cleaning,
No sanitation, …
• Worker Behavior Related Scenarios– No glove, No contact glove-case, Preslice products in the
morning, Do not slice product on gloves
• Growth Inhibitor Related Scenarios– All products with GI, No product with GI
• Cross contamination Related Scenarios– Separate slicers, No cross contamination
• Storage Temperature and Duration Related Scenarios– Temperature in compliance with FDA food code, Temperature set
so that no growth can occur
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Outline
• Design
• Data Sources
• Implementation
• Modeling Approach
• Verification
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Verifications
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General correspondence between the frequency of contamination vs. observed one (Cornell longitudinal study)
Important sources of contamination considered in the model (Risk mapping, Mock Deli study)
Control of the mass balance
Correspondence between the simulated bacterial density distribution vs. the observed one (NAFSS, 2008) (this graph)
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