# Presentation: 265586

## A Risk Assessment for Clostridium perfringens in Ready-to-Eat and Partially Cooked Meat and Poultry Products

- Dr. Edmund Crouch
- Cambridge Environmental, Inc.
- March 24, 2005

## Overview

- Context
- Risk Management questions
- Risk Assessment
- Foods Modeled
- Conceptual Model
- Dose-Response
- Results
- Answer to Risk Management Questions
- Risk Factors
- What-if scenario (example)
- Peer Review Comments
- Summary

**Overview**

## Context

- During processing of Ready-to-Eat (RTE) and partially cooked foods (PCF), raw meat and poultry are heat treated (lethality step), then cooled (stabilization step).

- Spores from pathogenic organisms may be activated by the heat treatment and germinate into vegetative cells.  These cells may grow at permissive temperatures during stabilization or subsequently.

## Context

- The USDA standard requires no growth of *C. botulinum*.  The risk assessment examines what effect changes in the CP standard would have on *C. botulinum*.

**Context**

## Risk Management (RM) Questions

- What is the impact on the probability of human illness if the allowable growth of CP* *is raised from 1-log10 during stabilization to 2-log10 or 3-log10?.
- What would the relative growth of *C. botulinum *(relative to the growth of CP) be for each of these stabilization standards?

## The Risk Assessment

- Foods modeled
- Exposure Assessment
- Dose-Response

## RTE and PCF Modeled

**A.**

-  Foods determined

- shelf stable

- excluded (261 entries)

** **

** **

**All consumed foods that contain meat **

** **

**or poultry in the Continuing Survey **
**of Food Intake by Individuals (CSFII)**

**(1625 entries)**

** **

**C.**

-  Foods with nitrites and

- >3%   salt

- content excluded

- (50 entries)

**B.**

-  Foods with high salt

- concentrations

-  (>8%)

- excluded (0 entries)

**D.**

-  Raw commodities

- excluded (707 entries)

**RTE or PCF**

**commodities modeled**

**(607 entries)**

## Conceptual Layout of Risk Assessment

- Plant-to-fork risk assessment that models the growth, survival and death of CP vegetative cells and spores from post-lethality at the processing plant to consumption by the consumer in a serving of RTE or PC meat and poultry.

**Notes:**
Read text above

## C. perfringens Risk Assessment Model

**Heat step**

**Eaten cold**** **

**Eat  **

- _Risk Assessment step_

- _Tracking of CP _

- _Data Sources_

- .

**Veg. cells grow**

- .

-      **Stabilization**

**Spores unaffected**

**     ****Spontaneous germination**

- .

**Some spores**
**germinate**

**Veg. cells**

-      **Storage at Home**

**Veg. cells **
**grow/die**

**Spores**
** ****unaffected**** **

-      **Storage at Plant and Retail**

**Veg. cells grow/ die**

**Spores unaffected**** **

-   **Cook**

**Re-Heat**

**Spores not **
**tracked**

**Veg. cells **
**grow/die**

-   **Hot-hold**

**Spores not **
**tracked**

**Veg. cells **
**grow/die**

- .

**Spores**

**RTE**

**PCF**

- Veg. cells

**Veg. cells**

- spores

**Preparation:**

**Hot-hold**

**Veg. cells**

**Spores**** ****activated**

**Consumption**

**Processing:**

**Storage:**

## Dose-Response

**Human clinical trial data used:**
- Requirements: CP type A, enterotoxin positive
**DR-curves:**
- Exponential within-strain
- Lognormal random between-strain effect
**Example:**
- Consumption of 4.8 **** 107 CP vegetative cells results in a 1% attack rate, on average.

## Results

- Answer to Risk Management (RM) Questions
- Risk Factors
- What-if scenario (example)

## Results of 1st RM Question

**1****st**** Risk Management (RM) Question:**
- What is the impact on the probability of human illness if the allowable growth of CP* *is raised from 1-log10 during stabilization to 2-log10 or 3-log10?

## Results 1st RM Question (continued)

- A change in growth during stabilization from 1 log10 to 2 log10 and 3 log10 results in a median 1.21 and 1.57 fold increase in annual diarrheal illness, respectively.

## Estimating the number of annual C. perfringens illness:

- Of the 153 CP outbreaks from 1990-1999, only one has been confirmed as having been caused by a RTE product, turkey loaf.
- The majority of CP outbreaks occur in institutional settings and are thought to be the result of meat prepared from _raw_.
- Mead *et al* (1999), using multipliers based on *Salmonella-*caused illnesses to account for underreporting of CP illnesses, estimated ~250,000 illnesses from CP annually for _all_ food sources.

## The number of predicted annual C. perfringens illness:

**The model estimate is:**
- Approximately 113,000 illnesses per year in the U.S. from RTE & PCF (at 1 log10 growth).
- However, the modeling has an uncertainty of at least a factor of 2.
- The model is a tool to evaluate the effect of interventions, rather than predict the absolute number of illnesses

## Possible Risk Factors Analyzed by the Risk Assessment Model

**Possible contributing factors are:**
- 	1) Stabilization at food processing plants
- Allowing a different CP growth during stabilization.
- 	2) Improper institution and consumer hot-holding
- Abusive holding of processed meat and poultry (*e.g.* banquets, buffet, etc.).
- 	3) Improper institution and consumer cold storage
- Storage temperatures set too high.
- Failure of refrigeration.

## 1. Results for illnesses due entirely to growth during stabilization

- Stabilization of RTE and partially cooked products allowing only 1 log10 growth contribute minimally to the burden of CP illness.

## Role of stabilization

- Stabilization of RTE and PCF at food processing plants contributes minimally (0.07%) to the risk of CP illnesses at 1 log10 growth during stabilization.

**Notes:**
Read text

## 2. Results for role of improper hot-holding

- Improper hot-holding contributes to approximately _4%_
- 	of the predicted illnesses; however, this is an underestimate:
- The model treats each serving as independent, but hot-held servings will usually be heated together and cross-contaminate other servings.
- The model likely underestimates illnesses by a factor close to the average number of servings heated and mixed together during hot-holding.

## Role of improper hot-holding

- Epidemiology finds that hot-holding contributes to more than 90% of reported CP outbreaks (typically cooked from _raw_ products). However, these data are biased toward institutional hot-holding as this will produce large detectable outbreaks.
- There is no independent estimate of the role of hot-holding among RTE and PCF (_these foods are not likely to be hot-held_.)

## 3. Results for role of improper cold-storage

- Improper cold storage accounts for most of the illness predicted by the model (93%).
- Temperatures and times were high and long enough to result in substantial growth of CP during storage:
- AI/FDA (1999) refrigerator temperatures at retail and home (up to 21 °C (70 °F)), and
- FDA/FSIS *Listeria monocytogenes* relative risk assessment (FDA/FSIS, 2003) (10-30 days); USDA hotline pilot questionnaire (up to 60 days).

## Risk Conclusions

**These results suggest:**
**Most of the risk for *****C. perfringens***** illnesses from RTE and partially cooked foods is not from food processing plants.**
**Principal risky activity is estimated to reside with institutions and consumers due to inadequate cold- and hot-holding.**** **

## Results of 2nd RM Question

**Results of 2****nd**** RM Question**

- Growth of CP is not predictive of growth of *C. botulinum*.

- _What would the relative growth of __*C. botulinum *__(relative to the growth of CP) be for each of these stabilization standards? _

**8.5 °C**

**12.5 °C**

## Analysis of ‘what-if’ scenario:

**To address CP growth predicted at low temperatures (13.9–21.1 °C (57–70 °F)), an alternative assumption was analyzed:**
- Competition with CP from psychrotrophic spoilage organisms (bacteria that optimally grow at low temperatures) at low temperatures.
- A formal analysis of spoilers would be needed to assess their impact on CP growth at low temperatures.  Due to the complexity and data intensive nature of such an analysis, a preliminary approach was performed to assess the impact of a more complete analysis.

## Effect of competing psychrotrophic spoilage at low temperatures

-     **Assumption**: CP does not grow 50% or 100% of time below 21.1 °C (70 °F)) due to the presence and growth of spoilage organisms during storage at retail and home.
**Results**:

| Assumption (no growth) | Annual illnesses at 1 log10 | Annual illness after assumption |
| --- | --- | --- |
| 50% | 113,000 | 60,500 |
| 100% | 113,000 | 7,900 |

## Conclusions of competing psychrotrophs at low temperatures ‘what-if’ scenario:

- The overall effect of this possibility is a lowering of the estimated total number of illnesses and an increase in the relative contribution of illnesses from abusive hot-holding.
- This would not affect the number of illnesses attributable to solely to growth during stabilization.

## Peer Review Comments

- Five External Reviewers were chosen
- CP microbiology (1)
- Food Safety (1)
- Food processing (1)
- Modeling (2)
- The overall review of the Risk Assessment report and model was positive.

## Peer Review Results

- Primary Reviewers criticism:
- Limited data available
- Greater clarification needed in the text
- No changes suggested in methodology
- No additional relevant data located
- Report updated
- Incorporates clarifications
- No change to calculations or results

## Summary

- A model was developed to determine the impact to public health of altering the current CP growth critical control limit.
- Approximately 113,000 illness/year are predicted to be caused by CP from consumption of RTE and PCF for growth at the current 1 log10 limit.  There are no data to validate this estimate.

## Summary

- Stabilization at food processing plants is not a significant source of CP foodborne illness at 1 log10 growth during stabilization, though some illnesses are associated CP growing in this process.
- The majority of illnesses are associated with improper cold storage of RTE and PCF.
- External peer review did not result in changes to the risk estimates

**Summary**