October 4, Microbial Risk Assessment Frameworks, Principles, and Approaches Rebecca Parkin, PhD, MPH Department of Environmental and Occupational Health Center for Risk Science and Public Health, School of Public Health and Health Services The George Washington University Medical Center

2 Purposes of MRA Predict population health risks linked to microbial pathogens –Food (fresh and processed) –Drinking water –Recreational water –Wastewater, runoff –Biosolids, manure –Modified organisms (contamination, cleanup) Estimate magnitude of disease burdens –Attributable risk –Source-specific risk Identify high risk sub- populations –Immune compromised –Dialysis, cancer patients –Infants, children –Elderly Guide policy decisions

3 Frameworks Underlying forms –Chemical risk assessment, 1983 (traditional) –Ecological risk assessment, 1990’s (systems) Microbial Risk Assessment Frameworks –National Research Council (NRC), 1983 –Modified NRC (used internationally), 1990’s –International Life Sciences Institute (ILSI) & EPA, 2000

4 ILSI/EPA Framework

5 Guiding Concepts Ordered, iterative process –Complete source-response pathway assessments –Use field & clinical measurements –Build modules Flexible structure –Accommodate different pathogens, contexts, scenarios, dynamics Assess impacts –Assumptions, data limitations Meaningful, useful products –Open, transparent processes

6 Key Challenges Problem formulation –What is THE problem? –How can it be modeled? –For what purpose? Comprehensiveness of approach –Analytic plan (sources & use of data) –Model development –Linkages of dynamic ecological & population scale disease models Compatibility of model structure & components with complexity of the problem Evaluation of the model –Analysis of uncertainty & variability –Explicit identification of assumptions –Use of probabilistic methods