# Presentation: 163361

## FSIS Listeria Risk Assessment

- Daniel Gallagher
- Dept. of Civil & Environmental Engineering
- Virginia Tech

- Eric Ebel and Janell Kause
- FSIS Risk Assessment Division
- USDA

- Listeria Public Meeting
- February 26, 2003

## Overview

- FDA *Listeria* risk ranking of RTE products
- FSIS Risk Management Questions
- FSIS *Listeria *Risk Assessment Model
- Data Inputs and Assumptions
- Model Implementation
- Risk Assessment Outputs
- Summary of Findings

## FDA Risk Ranking of RTE Products

- Approach:  Relative Risk Ranking of Food Categories
- Purpose:  Identify foods that pose the greatest public health risk and focus resources accordingly
- Evaluated Lm from retail to public health
- Available public comment
- Version 2 to be released

## FSIS Listeria Risk Management Questions

- Examine the effectiveness of testing and sanitation of food contact surfaces on mitigating product contamination, and reducing the subsequent risk of illness
- Evaluate the effectiveness of other interventions (e.g., pre- and post-packaging interventions)
- Provide guidance on how frequently to test and sanitize food contact surfaces for *Listeria* spp.

## Possible Sources of Lm in RTE Products at Retail

- Inadequate lethality during processing
- Direct deposition from non-food contact surface
- Transfer from food contact surface

****** ****Focus on food contact surfaces as the source of Lm**

## Model Description

- Dynamic “in-plant” *Monte Carlo* model predicts Lm concentrations at retail
- Coupled with an updated version of the FDA *Listeria* risk assessment model to predict human health impacts
- Mass balance approach –track bacteria as move from one media to another
- Incorporates FCS testing, product testing, sanitation, pre- and post-packaging interventions, growth inhibitors
- Conducted on deli meats (“high risk”)

## Conceptual Model,

- Part 1

## Conceptual Model,

- Part 2

## Risk Assessment Outputs

- The risk of illness or death on a per annum basis from Lm in deli meat as a function of:
- Testing (*Listeria *spp.) and sanitation frequency (based on plant size) of food contact surfaces
- Testing (Lm) and disposition of RTE product
- Pre- and post-packaging interventions
- The likelihood of detecting Lm in a product lot if a FCS tests positive for *Listeria *spp.

## Key Data Requirements

- Contamination Events
- frequency, duration, levels
- Transfer coefficients from FCS to product
- Lm to Lspp ratios
- Line production levels by plant size

## Contamination Event: Frequency

- Data source: FSIS IDV data
- Date description: Lspp prevalence over time for various food contact surfaces
- Method: Fit with survival analysis
- Results: Log normal distribution
- Mean time between contamination events: 23.1 days
- Standard deviation:  38 days

## Contamination Event: Duration

- Data Source: Tompkin 2002
- Data description: Sequential weekly Lspp positives for food contact surfaces
- Method: Fit with survival analysis
- Results: log normal distribution
- Mean: 8.8 days
- Standard deviation: 2.1 days

## Transfer Coefficients

- Data Source: published literature
- Results:
- Montville et al. (2001) and Chen et al. (2001) found that transfer coefficients of bacteria were log normally distributed.  Range: 0.01% to 10%  Standard deviation ~ 1 log
- Midelet & Carpentier (2002) found that after 12 contacts, 60%-100% of initial Lm transferred, ~100% of other bacteria.
- LMRA uses a log mean of –0.14 with a log SD of 1.  Truncate to 100% at max.

## Lspp to Lm Ratio

- Data Source: prevalence data provided in Tompkin (2002) and blinded industry data (no available *Listeria* level data)
- Assumption: prevalence ratio used for level ratio
- Results: ratios fit (truncated) normal distribution
- Mean: 52.6%
- Standard deviation: 26.7%

## Production Levels/ Lot Volumes by Plant Size

- Data source: FSIS RTE Survey
- Lot size per line per shift varies by plant size:
- Large: 48%, 19000 lb ± 14000
- Small: 48%, 7100 lb ± 10600
- Very Small: 4%, 2800 lb ± 9500
- Assume that FCS area varies proportionately.

## Contamination EventAdded Lspp to Food Contact Surface

- Source: No available data (calibrated data input)
- Assumption: Added levels are log normally distributed
- Method: Calibrate the added levels so that the predicted Lm distribution at retail matches the FDA retail distribution

## Model Calibration

- FDA Lm concentration distribution at retail
- Prevalence of Lm in product
- Levine et al. (2001) found prevalence from 0.52% - 5.16% in RTE meat and poultry.  Generally decreasing with time.  Generally 1-3% in 1999.
- Luchansky (in press) found 1.6% prevalence in frankfurter packages
- NFPA (2002) found 0.9% prevalence in RTE meat

## Preliminary USDA DataCY 2002

- HAACP code 03G (fully cooked, not shelf stable)
- subcategory: sliced, diced, shredded (e.g. sliced ham, sliced bologna, sliced chicken breast, diced chicken)
- 23 Lm positives out of 997 samples
-  prevalence of 2.3%

## Model Implementation and Baseline Data

## Data Entry Screens and Baseline Data

## Data Entry Screens and Baseline Data

## Data Entry Screens and Baseline Data

## Data Entry Screens and Baseline Data

## Data Entry Screens and Baseline Data

## Data Entry Screens and Baseline Data

## Output Screens

## Output Screens

## Results: Lot Timeline

## Post processing Growth ?

- FDA model assumes about 1.9 logs of growth on average between processing and retail.

| Source | % at Processing | % at Retail |
| --- | --- | --- |
| FSIS | 1% - 3%
measured | ? |
| NFPA | ? | 0.9%
measured |

-  LMRA uses same approach as FDA but with less growth (1 log vs 1.9 logs).  Lack of variability may impact growth-inhibiting-packaging conclusions.

## Analysis of growth

- Production
- Log(Lm per gram)

- Growth
- Log(Growth)

- =

- Retail
- Log(Lm per gram)

- +

- Normal(μ1,σ1)

- Normal(μ2,σ2)

- Normal(μ1+μ2, σ21 +σ22)

- +

- =

- Given a retail distribution,
- solve for production distribution
- for different assumed growth distributions.

*Then examine implied sample prevalence levels*
*assuming a test positive threshold of 1 Lm organism*
*in 25 gram samples.*

## Case 1

- +

- =

## Case 2

- +

- =

## Case 3

- +

- =

## Mass Balance:  Tracking Lspp on FCS

## Model Evaluation

## Comparison of FSIS Model Outputs to FDA Risk Assessment Inputs

## Baseline predictions

- Calibration to “average” updated FDA/FSIS model Lm concentration in retail deli meat distribution
- Lack of uncertainty about concentration has small effect on uncertainty about public health predictions
- In-plant baseline predictions repeatable

- Median, 5th and 95th percentiles
- in predicted elderly deaths

## Model Stability

## Model Results

## Scenarios Tested

- Baseline calibration: no testing, no interventions, no post-processing, no GIP
- FCS Testing Levels, test and hold yes, dispose product yes, test lot yes, enhanced cleaning yes  (No. tests per line per month for large, small, very small plants)
- 4-2-1
- 8-4-2
- 10-10-10
- 16-8-4
- 32-16-8
- 60-60-60
- 60-60-60 Lot testing, dispose product yes
- 100% post-processing treatment (90% - 95% effective) for all three plant sizes, no testing
- 100% growth-inhibiting packaging (90% 95% effective) for all three plant sizes, no testing

- All scenarios tested for production of 1,000,000 lots.

## FCS Testing/Sanitation Impacts

## Contingency Table: Likelihood of Detecting Listeria spp./Lm

- Overall FCS prevalence of ~ 13.7%
- Overall Lot prevalence of ~2.2%
- Lot prevalence when FCS is positive ~15.7%
- FCS testing improves lot testing by factor of 7

- 60-60-60 FCS tests, 60-60-60 lot tests, test and hold in place

## Test and Hold Comparison

## Test and Hold Evaluation

- Overall FCS prevalence approximately constant at ~13-14 % regardless of test and hold.
- Overall lot prevalence 15-16% if test and hold, 4-5% if not test and hold
- Recall overall lot prevalence ~2.2%
- For retail Lm, test and hold only significant at more frequent FCS testing

## Sensitivity Analysis

## Sensitivity Analysis: Sampled RTE Mass

## Sensitivity Analysis: FCS Area Tested

## Sensitivity Analysis: FCS Area Tested

## Sensitivity Analysis: Post processing

## Evaluation of prevalence for different Lm/Lspp ratios 

- Each new ratio requires a recalibration to match the observed Lm distribution at retail.  These results are preliminary

## Sensitivity Analysis Findings

**** RTE sampled mass, **** retail Lm
- Mass should be limited only by lab considerations.
**** FCS area sampled,  retail Lm
- Caution: assumes Lm evenly distributed
- FCS testing is effective for a wide range of Lm/Lspp ratios.  The effectiveness is higher at higher ratios.
**** Post processing & industry participation, **** ****  retail Lm

## Public Health Impacts

## Predicted elderly deaths from deli meats

## Predicted intermediate age deaths from deli meats

- Predicted intermediate age deaths from deli meats

## Predicted neonatal deaths from deli meats 

## Predicted lives saved relative to baseline

| Scenario | Elderly | Intermediate |  | Neonates |  | Total |
| --- | --- | --- | --- | --- | --- | --- |
| 4-2-1 | 20 | 4 | 1 |  | 25 |  |
| 8-4-2 | 30 | ? | ? |  | 30 |  |
| 10-10-10 | 40 | ? | ? |  | 40 |  |
| 16-8-4 | 30 | ? | ? |  | 30 |  |
| 32-16-8 | 60 | ? | ? |  | 60 |  |
| 40-20-10 | 70 | 15 | 4 |  | 89 |  |
| 60-60-60 | 120 | 27 | 7 |  | 154 |  |
| 60-60-60 RTE | 120 | 26 | 7 |  | 153 |  |
| PP-95% | 120 | 26 | ? |  | 146 |  |
| PP-99% | 173 | 39 | 10 |  | 221 |  |
| GIP | 110 | 25 | ? |  | 135 |  |
| PP-95% & GIP | 186 | 41 | 11 |  | 238 |  |

## Test and control combinations

- Note:  Testing is non-additive with post-processing treatment.

## Model Variables

- Only considers food contact surface as source of Lspp/Lm in product
- Only a “generic” food contact surface
- Assumes Lspp evenly distributed across food contact surface, and Lm evenly distributed within product
- Operates on a product lot basis

## Summary Findings

- Food contact surfaces found to be positive for *Listeria *species greatly increased the likelihood of finding RTE product lots positive for Lm (x7 if test and hold, x2 if not) ).
- Frequency of contamination of FCS with *Listeria *species appears to encompass a broad timeframe, and the duration of contamination lasts about a week.
- The proposed minimal frequency of FCS testing/sanitation, as presented in the proposed rule (66 FR 12589, Feb. 27, 2001) results in a small reduction in the levels of Lm in deli meats at retail.
- Increased frequency of testing/sanitation leads to proportionally lower risk of listeriosis.
- Combinations of interventions appear to be much more effective than any single intervention in mitigating the potential contamination of RTE product with Lm and reducing the subsequent risk of illness or death.

## Questions?

## Lm Distributions at Retail for Scenarios Tested

## Health Impacts for Scenarios Tested