Quantitative Microbial Risk Assessment

Charles N. Haas is the head of the department of Civil, Architectural and Environmental Engineering at Drexel University and the Betz Chair Professor of Environmental Engineering.  He has served on numerous advisory committees of the US EPA and the National Research CouncilJoan Rose serves as the Homer Nowlin Chair in Water Research at Michigan State University, the Co-Director of the Center for Advancing Microbial Risk Assessment (CAMRA) and the Director of the Center for Water Sciences (CWS).  She is a member of the National Academy of Engineering.Charles P. Gerba is a Professor in the department of Soil, Water and Environmental Science at the University of Arizona. He is the author of 11 books and over 400 journal papers. Dr. Gerba is a member of the U.S. Environmental Protection Agency's Science Advisory Board Committees on Drinking Water and Research Strategies.

• Preface xiChapter 1 Motivation 1Prevalence of Infectious Disease 1Prior Approaches 4Scope of Coverage 4Potential Objectives of a QMRA 5Site-Specific Assessment 5Ensemble of Sites 6Secondary Transmission 7Outbreaks versus Endemic Cases 7References 10Chapter 2 Microbial Agents and Transmission 15Microbial Taxonomy 15Eukaryotes 15Prokaryotes 18Viruses 20Prions 22Clinical Characterization 24Microorganisms of Interest 27Viruses 27Bacteria 37Protozoa 42Transmission Routes 45Inhalation 48Dermal Exposure 50Oral Ingestion 50References 55Chapter 3 Risk Assessment Paradigms 63Chemical Risk Assessment: National Academy of Sciences Paradigm 63Ecological Risk Assessment 67Approaches for Assessing Microbial Risks 71Background 71The QMRA Framework 74Hazard Identification 74Dose–Response Assessment 74Exposure Assessment 76Risk Characterization 77Risk Management 79Development of the QMRA Framework and Processes 79QMRA and the Safety of Water 82QMRA, Food Safety, and the HACCP System 84References 86Chapter 4 Conducting The Hazard Identification (HAZ ID) 91Identifying and Diagnosing Infectious Disease 92Health Outcomes Associated with Microbial Infections 95Sensitive Populations 100Women during Pregnancy, Neonates, and Young Babies 101Diabetes 102The Elderly 102The Immunocompromised 104Databases for Statistical Assessment of Disease 106ICD Codes 107Waterborne and Foodborne Outbreaks 111Epidemiological Methods for Undertaking HAZ ID 117Controlled Epidemiological Investigations 118HAZ ID Data Used in the Risk Assessment Process 119Recommendations for Updating Quantitative Data for HAZ ID Information 121References 122Chapter 5 Analytical Methods and The QMRA Framework: Developing Occurrence and Exposure Databases 129Introduction 129Approaches for Developing Occurrence and Exposure Databases 132Overview of Methodological Issues 134Sampling Water 136Sampling Surfaces and Food 138Sampling Aerosols 138Specific Techniques for Bacteria, Protozoa, and Viruses 140Bacteria 140Protozoa 142Viruses 143Molecular Techniques 145Probes (FISH) 146Typing 146Metagenomics 147PCR and Quantitative PCR 147References 151Chapter 6 Exposure Assessment 159Conducting the Exposure Assessment 159Characterizing Concentration/Duration Distributions 160Random (Poisson) Distributions of Organisms 160Estimation of Poisson Mean in Count Assay (Constant and Variable Volumes) 162Count Assay with Upper Limits 163Estimation with Quantal Assay 164Goodness of Fit to Poisson: Plate Assay 168Goodness of Fit: MPN 178Confidence Limits: Likelihood 182Implications for Risk Assessment 187Consumption Distributions 214Systematic Subpopulation Differences 221Afterword 223Appendix 224Microsoft Excel 224MATLAB 225R 227References 230Chapter 7 Predictive Microbiology 235Objective 235Basic First-Order Processes and Deviations 236Biological and Physical Bases for Deviations 236Physical Removal 238Types of Decay Processes 238General Forms of Decay and Reasons for Nonlinearity 238Spontaneous/Endogenous 240Chemical Agents 241Thermally Induced 243Ionizing and Nonionizing Radiation 243Predation and Antagonism 245Types of Growth Processes 245Mathematical Modeling of Growth Curves 246Substrate Dependency 252Structured Growth Models 255Incorporation of Decay into Growth Models 256Systems Biology Approaches 258Dependence of Growth Parameters on Other Environmental Variables 258Interacting Populations 258Data Sources 260References 263Chapter 8 Conducting The Dose–Response Assessment 267Plausible Dose–Response Models 268Framework for Mechanistic Dose–Response Relationships 269Exponential Dose–Response Model 271Beta-Poisson Dose–Response Model 272Simple Threshold Models 274Negative Binomial Dose Distributions 277Variable Threshold Models 278Other Mixture Models 279Biological Arguments for One-Hit Models 281Empirical Models 282Fitting Available Data 283Types of Data Sets 284Potential Impacts of Immune Status 298Relationship between Dose and Severity (Morbidity and Mortality) 299Morbidity Ratio (PD:I) 299Mortality Ratio 303Reality Checking: Validation 304Validation: 1993 Milwaukee Outbreak 304Use of Indicators and Other Proxy Measures in Dose–Response 305Indicator Methods 305Molecular Methods 307Advanced Topics in Dose–Response Modeling 308Dose–Response–Time Models 308Physiological Models 313Appendix 315References 317Chapter 9 Uncertainty 323Point Estimates of Risk 324Terminology: Types of Uncertainty 326Sources of Uncertainty 327Sources of Variability 328Variability that is Uncertain 329Approaches to Quantify Parametric Uncertainty 329Likelihood 329Bootstrap 330Other Methods 330Applications 332Exposure Assessment 332Dose–Response Assessment 338Combining Parametric Uncertainty from Multiple Sources 344Propagation Methods 344Monte Carlo Analyses 347Overall Risk Characterization Example 365Second-Order Methods 368Model Uncertainty and Averaging 370References 373Chapter 10 Population Disease Transmission 377Introduction: Models for Population and Community Illnesses 377Basic SIR Model 378Incubation Period 386Duration of Illness 388Secondary Cases 389Impact of Immunity 392Outbreak Detection 393References 397Chapter 11 Risk Characterization and Decision Making 399Introduction 399Valuing Residual Outcomes 400Classical Economics 400DALYs and QALYs 404Decision Making 407Cost–Benefit Analysis 408Multivariate Approaches 411Other Aspects Entering into a Decision 412Equity and Justice Aspects 412References 413Index 415