quantitative exposure assessment for pathogens in cooked meat and ready-to-eat snack foods

143 Pages·2011·1.77 MB·English

DEVELOPMENT OF A QUANTITATIVE MICROBIAL RISK ASSESSMENT MODEL FOR
FOODBORNE PATHOGENS IN HERBS AND SPICES

A Thesis
Presented to
The Faculty of Graduate Studies
of
The University of Guelph

by
ANDREW FEDORUK

In partial fulfillment of requirements
for the degree of
Master of Applied Science
February, 2011

©Andrew Fedoruk, 2011
AUTHOR DECLARATION

I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis,
including any required final revisions, as accepted by my examiners.

I understand that this thesis may be made available to the public electronically.
ABSTRACT

DEVELOPMENT OF A QUANTITATIVE MICROBIAL RISK ASSESSMENT MODEL FOR
FOODBORNE PATHOGENS IN HERBS AND SPICES

Andrew Fedoruk Advisors:
University of Guelph, 2011 Dr. Valerie J. Davidson
Mr. Aamir M. Fazil

Recent recalls and outbreaks have raised public awareness of herbs and spices as
a potential vehicle for foodborne illness. As an initial step towards risk management,
quantitative microbial risk assessment models were developed to estimate the potential
for spices to cause illness in two high risk food-pathogen combinations. The models
simulated contamination levels and prevalence in primary and spice ingredients
separately during preparation and storage stages, taking into account intrinsic and
extrinsic factors which allowed for changes in levels of contamination over time. Per
serving and per annum risk estimates illustrated the relative potential for spices to
contribute to illness for different scenarios and can be used to identify strategies for
minimizing risk. Model sensitivity analysis suggested that initial contamination and
storage periods were the most influential variables in terms of affecting overall rate of
illness. The reliability of the model, data gaps, and areas for future research were
discussed.
ACKNOWLEDGEMENTS

I would like to thank everyone who has assisted me in completing this thesis.

Firstly, I would like to thank my advisor, Dr. Valerie J. Davidson, P.Eng. Without her
direction and extensive knowledge of food safety and risk assessment, this thesis would
not have been possible.

Secondly, I would also like to thank Mr. Aamir Fazil from Public Health Agency of Canada
for assisting in advising this project and for steering me in the right research direction
during times of disarray.

I would also like to thank Mr. David Jennison from Gay Lea Foods Co-operative Limited
for kindly providing information regarding the manufacturing of food products, and Dr.
Donald W. Schaffner from Rutgers University for providing his insight and for serving as
an invaluable resource for this project.

Finally, I would like to thank Jessica for her encouragement and for providing me with a
positive outlook throughout my career in graduate studies. Her companionship and
loving support has sustained me to complete this degree.

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ........................................................................................................ i
LIST OF TABLES .................................................................................................................... v
LIST OF FIGURES ................................................................................................................. vi
LIST OF SYMBOLS & ACRONYMS ...................................................................................... vii
Chapter 1 : Problem Statement .......................................................................................... 1
Chapter 2 : Literature Review ............................................................................................. 3
2.1 Microbial Risk Assessment ................................................................................... 3
2.2 Physical Properties of Herbs and Spices ............................................................... 5
2.3 Microbial Contamination in Herbs and Spices ..................................................... 7
2.3.1 Summary of Investigations Linked to Herb and Spice Contamination .......... 8
2.3.2 Recalls of Herbs and Spices ......................................................................... 10
2.3.3 Types of Contamination Found in Herbs and Spices ................................... 11
2.3.4 Pathogen Prevalence in Herbs and Spices .................................................. 13
2.3.5 Reducing Microbial Contamination in Herbs and Spices ........................... 13
2.4 Review of Food Safety Quantitative Microbial Risk Assessment Techniques .... 15
2.4.1 Development of Microbial Risk Assessment Techniques ............................ 16
2.4.2 Stochastic Modeling Approaches in QMRA ................................................ 18
2.5 Literature Deficiencies ........................................................................................ 22
Chapter 3 : Research Objectives ....................................................................................... 24
Chapter 4 : Modeling Approaches .................................................................................... 25
4.1 Monte Carlo Simulation & Uncertainty Representation .................................... 25
4.2 Risk Characterization .......................................................................................... 26
4.3 Sensitivity Analysis ............................................................................................. 26
Chapter 5 : (Case Study 1) Estimating the Risk of Salmonellosis from the Consumption
of Dairy-Based Snack Food Dips ....................................................................................... 28
5.1 Background ........................................................................................................ 28
5.2 Model Development ........................................................................................... 30
5.2.1 Model Outline ............................................................................................. 30
5.2.2 Primary assumptions of model ................................................................... 30
5.2.3 Initial Contamination Levels ........................................................................ 31
5.2.4 Contamination Levels Following Mixing ..................................................... 33
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5.2.5 Prevalence of Salmonella spp. in Spices ...................................................... 33
5.2.6 Modeling Changes in Microbial Levels ........................................................ 36
5.2.7 Storage Time Estimates .............................................................................. 38
5.2.8 Dose-Response Model ................................................................................. 39
5.2.9 Consumption Patterns................................................................................. 40
5.2.10 Summary of Uncertainty Distributions Used for Model Inputs ................... 41
5.3 Model Results ..................................................................................................... 42
5.3.1 Effects of Composition and Storage Temperature on Risk of Illness .......... 42
5.3.2 Public Health Impact ................................................................................... 43
5.3.3 Sensitivity Analysis ...................................................................................... 47
5.3.4 Summary of Findings ................................................................................... 48
5.4 Discussion of Model Results ............................................................................... 49
5.4.1 Data Quality ................................................................................................ 50
5.4.2 Selection of the Microbial Survival Model .................................................. 52
5.4.3 Dose-Response Model ................................................................................. 54
5.4.4 Sensitivity Analysis ...................................................................................... 54
5.4.5 Limitations in Model Framework ................................................................ 56
5.4.6 Validation of Public Health Impact Estimates ............................................. 57
Chapter 6 : (Case Study Two) Estimating the Risk of Clostridium Perfringens Food
Poisoning from the Consumption of Cooked Meats ........................................................ 58
6.1 Background ........................................................................................................ 58
6.2 Model Development ........................................................................................... 60
6.2.1 Model Outline ............................................................................................. 60
6.2.2 Primary assumptions of model ................................................................... 61
6.2.3 Initial Contamination Levels ........................................................................ 62
6.2.4 Contamination Levels Prior to Cook Step .................................................... 65
6.2.5 Prevalence of Illness-Causing Clostridium Perfringens ............................... 66
6.2.6 Reduction of Vegetative Cells during the Cooking Step .............................. 67
6.2.7 Time-Temperature Cooling Profiles ............................................................ 69
6.2.8 Modeling Microbial Growth during Cooling/Stabilization .......................... 72
6.2.9 Dose-Response Model ................................................................................. 75
6.2.10 Consumption Patterns................................................................................. 76
6.2.11 Summary of Uncertainty Distributions Used for Model Inputs ................... 77
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6.3 Model Results ..................................................................................................... 78
6.3.1 Effects of Variations in Cooling Relationships on Risk of Illness ................. 78
6.3.2 Public Health Impact ................................................................................... 79
6.3.3 Sensitivity Analysis ...................................................................................... 82
6.3.4 Summary of Findings ................................................................................... 83
6.4 Discussion of Model Results ............................................................................... 84
6.4.1 Data Quality ................................................................................................ 85
6.4.2 Dose-Response Model ................................................................................. 87
6.4.3 Selection of the Microbial Growth Model ................................................... 88
6.4.4 Sensitivity Analysis ...................................................................................... 88
6.4.5 Limitations in Model Framework ................................................................ 89
6.4.6 Validation of Public Health Impact Estimates ............................................. 92
Chapter 7 : Overall Discussion & Future Research ........................................................... 93
7.1 Areas for Future Research .................................................................................. 93
7.1.1 Case Study 1: Salmonella spp. in dairy-based dips ..................................... 94
7.1.2 Case Study 2: Clostridium perfringens in cooked meats ............................. 95
7.1.3 Modeling the effects of Irradiation ............................................................. 96
7.2 Regulatory Criteria on Herbs and Spices ............................................................ 97
7.3 Conclusions & Final Recommendations............................................................ 100
References ....................................................................................................................... 102
Appendices ...................................................................................................................... 113
Appendix A: ..................................................................................................................... 115
Appendix B: ..................................................................................................................... 117
Appendix C: ...................................................................................................................... 119
Appendix D: ..................................................................................................................... 120
Appendix E: ...................................................................................................................... 121
Appendix F: ...................................................................................................................... 124
Appendix G: ..................................................................................................................... 125
Appendix H: ..................................................................................................................... 127
Appendix I: ....................................................................................................................... 129
Appendix J: ...................................................................................................................... 131

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LIST OF TABLES

Table 2.1: Physical Properties and Characteristic of Common Herbs and Spices ........................................... 6
Table 2.2: Summary of Canadian Food Inspection Agency Herb and Spice Recalls from 2005 to 2010 ....... 10
Table 2.3: Properties of Common Pathogens Found in Herbs and Spices and their Potential Impact on
Public Health ................................................................................................................................ 12
Table 2.4: Summary of Pathogen Prevalence in Spices from the Literature................................................. 13
Table 5.1: Summary of outbreak investigations used for data on initial counts of Salmonella spp. in dried
spices ............................................................................................................................................ 32
Table 5.2: Summary of microbial surveys measuring Salmonella spp. prevalence in dried spices ............... 34
Table 5.3: Prevalence of Salmonella spp. contamination in snack food dips from spice ingredients .......... 35
Table 5.4: Summary of parameters used to model uncertainty for Salmonella spp. rates of decline.......... 38
Table 5.5: Summary of parameters used to model uncertainty for storage times ....................................... 39
Table 5.6: Beta-Poisson coefficients used in dose-response modeling ....................................................... 40
Table 5.7: Summary of uncertainty representation in model input variables for Case Study 1 ................... 41
Table 5.8: Mean probability of illness for consumption of contaminated snack food dips: domestic
preparation ................................................................................................................................... 42
Table 5.9: Mean probability of illness for consumption of contaminated snack food dips: commercial
production .................................................................................................................................... 43
Table 5.10: Mean public health impact associated with domestic preparation of snack food dips ............. 45
Table 5.11: Summary of results from probability distribution of public health impact from spice
ingredients .................................................................................................................................... 47
Table 6.1: Initial levels of CPE spores from contaminated spice ingredients................................................ 63
Table 6.2: Summary of microbial surveys used for data on initial counts of Clostridium perfringens in raw
meat ............................................................................................................................................. 64
Table 6.3: Initial levels of CPE spores from contaminated meat ingredients ............................................... 65
Table 6.4: Prevalence of CPE spore contamination in spice ingredients ...................................................... 66
Table 6.5: Prevalence of CPE spore contamination in raw meat ingredients ............................................... 67
Table 6.6: Modeled vegetative cell levels in meat prior to and following the cooking step ........................ 68
Table 6.7: Summary of Time-Temperature Cooling Profiles Implemented for Dynamic Growth of CPE ..... 70
Table 6.8: Parameter estimations used for dynamic growth predictions in cooling profiles 1 to 3 ............. 74
Table 6.9: Summary of parameters used to model uncertainty in CPE net growth during stabilization ...... 75
Table 6.10: Summary of Case Study 2 uncertainty representation in model calculations ........................... 77
Table 6.11: Mean exposure and probability of illness estimates for consumption of contaminated cooked
meat for different sources of contamination ............................................................................ 79
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Table 6.12: Mean public health impact associated with consumption of contaminated cooked meats
following stabilization for different sources of contamination ................................................. 80
Table 6.13: Summary of results from the probability distribution of public health impact from spice
contamination in cooked meats ................................................................................................ 82
Table 7.1: Efficacy of irradiation treatment on the decontamination of mesophilic bacteria in selected
dried spices ................................................................................................................................... 97

LIST OF FIGURES

Figure 2.1: Typical Exposure Assessment Pathways Modeled in Food Safety Microbial Risk Assessment ..... 4
Figure 2.2: Monte Carlo analysis example for exposure assessment of bacteria in meat during processing
...................................................................................................................................................... 20
Figure 5.1: Exposure pathway outline of Salmonella spp. in dairy-based snack food dips ........................... 30
Figure 5.2: Development process for modeling survival of Salmonella spp. in snack food dips .................. 37
Figure 5.3: Uncertainty distribution of public health impact from spice ingredients ................................... 46
Figure 5.4: Relative significance of model variables on public health impact estimates: ............................. 48
Figure 6.1: Exposure pathway outline for Type A enterotoxin-producing Clostridium perfringens (CPE) in
cooked meats ............................................................................................................................... 60
Figure 6.2: Summary of microbial surveys used for initial counts of Clostridium perfringens in spices ....... 62
Figure 6.3: Cooling Profile 1 – USDA-FSIS standards for cooling of uncured meat and poultry ................... 70
Figure 6.4: Cooling Profile 2 - Literature cooling profile for a beef roast in cold air ..................................... 71
Figure 6.5: Cooling Profile 3 - Literature cooling profile for a beef roast in cold water................................ 71
Figure 6.6: Uncertainty distribution of public health impact from spice ingredients in cooked meats for
different scenarios ........................................................................................................................ 81
Figure 6.7: Relative significance of model variables on public health impact estimates: ............................. 83

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LIST OF SYMBOLS & ACRONYMS

Acronyms
CDC – Centers for Disease Control and Prevention
CFIA – Canadian Food Inspection Agency
CFU – Colony forming units
CPE – Clostridium perfringens enterotoxin-producing strains
FAO – Food and Agriculture Organization of the United Nations
FDA – United States Food and Drug Administration
FSIS – Food Safety & Inspection Service
QMRA – Quantitative Microbial Risk Assessment
PHAC – Public Health Agency of Canada
spp. – species of Salmonella bacteria
USDA – United States Department of Agriculture

Mathematical Symbols
α – Beta-Poisson dose-response model parameter
β – Beta-Poisson dose-response model parameter
τ – Spearman’s rank correlation coefficient
µr – Rate of decline of Salmonella spp. in snack food dip
aw – Water activity
Cc – Concentration of Clostridium perfringens vegetative cells on cooked meat following cooling
Cm – Concentration of pathogens following mixing
Cp – Initial contamination levels in primary ingredient
Cs – Initial contamination levels in spice ingredients
Dc – Exposure dose from consumption of a single serving
Fg – Fraction of spores that germinate during cook step
Gc – Growth of vegetative cells during cooling/stabilization
Gy – (Gray) unit of absorbed ionizing radiation
Ip – Estimated annual number of illnesses for a population
k – Exponential dose-response model parameter
Lc – Probability that food product is contaminated with pathogens
Lm – Probability that raw meat is contaminated with pathogens
Ls – Probability that spice ingredients are contaminated with pathogens
mc – Mass of food product consumed per year per capita
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