Risk Assessment -1 Quantitative Microbial Risk AssessmentSlide 2Slide 3Approaches to Risk EstimationRisk Assessment ParadigmsKinds of Environmental Risk AssessmentsImportant Differences Between Microbial & Chemical Risks: the ChemicalImportant Differences Between Microbial & Chemical Risks: The MicrobialQuantitative Microbial Risk AssessmentExposure, Level of Protection and Microbial Risk: The RelationshipSlide 11RISK ASSESSMENT FOR ENVIRONMENTALLY TRANSMITTED PATHOGENS: ILSI/EPA PARADIGMSlide 13Slide 14Conducting Hazard Identification for MicrobesSlide 16Slide 17Exposure AssessmentCHARACTERIZATION OF EXPOSURE - ELEMENTS INCLUDED IN PATHOGEN CHARACTERIZATION: OCCURRENCESlide 20Slide 21Pathogen Characteristics or Properties Favoring Environmental TransmissionSlide 23Slide 24Slide 25Slide 26Slide 27Slide 28Other Pathogen Characteristics or Properties Favoring Environmental TransmissionCHARACTERIZATION OF EXPOSURE: ELEMENTS CONSIDERED IN EXPOSURE ANALYSISSlide 31Outcomes of Infection Process to be QuantifiedCHARACTERIZATION OF HUMAN HEALTH EFFECTS: ELEMENTS OF HOST CHARACTERIZATIONSlide 34Characteristics or Properties of Pathogens -Interactions with HostsElements That May be Included in Dose-Response AnalysisSlide 37Dose-Response Data and Probability of Infection for Human RotavirusDose-Response Models and Extrapolation to Low Dose RangeSlide 40Slide 41Slide 42Probabilities of Exposure and InfectionProbability of ExposureExponential Dose-Response ModelBeta-Poisson Dose-Response ModelRotavirus Dose-Response Relationships: Experimental Data, Exponential Model and Beta-Poisson ModelDaily and Annual Risks of Various Outcomes from Exposure to Water Containing RotavirusesHuman Infectivity of Norwalk VirusComparing Risks of Disease AgentsDesirable attributes of an integrated measure of riskRisk Assessment -1Quantitative Microbial Risk Assessment ENVR 890-2Mark D. SobseySpring, 2009WHO Health-Risk Based Framework: Application to WHSThese principles apply to all types of WSH activitiesWHO Health-Risk Based Framework: Application to WHS•A risk-based framework•Source-to-consumer management approach to protection from exposure to environmental agents •Establishes health based-targets for control (specific microbes and chemicals)•Sets acceptable level of risk appropriate to setting and population•Helps establish and carry out Management Plans (Safety Plans) to achieve control•Includes independent surveillance•Is an integrated, proactive approach•Consistent across, compatible with and applicable to all WSH measuresApproaches to Risk Estimation•Direct Approach: Epidemiological Analysis–Ex. Intervention trial (RCT) or Prospective Cohort Study–Has been used to assess risk from drinking water, recreational water and reclaimed water exposures–Problems with sensitivity (sample size issue)–Trials can are expensive (esp. in developed countries)•Indirect approach: Mathematical models–Modeling system: ex.: Risk Assessment–Must account for properties of infectious disease processes–Pathogen specific models–Uncertainty and variability may make interpretation difficult•Combined Epidemiological/Quantitative Microbial Risk Assessment– Dynamic modeling of disease risks in exposed populations under defined environmental conditions –uses analytical tools and data from both epidemiology and QMRARisk Assessment ParadigmsNational Academy of Sciences ParadigmHazard Identification and Problem Formulation are synonymous“Analysis” corresponds to “Exposure Assessment” and “Health Effects Assessment”Risk Characterization is the main outputIInforms risk management, decision-making and policy; iterative & dynamic process US EPA Integrated Risk Assessment ProcessKinds of Environmental Risk AssessmentsHuman health risk assessment•characterize potential adverse health effects of human exposures to environmental hazards. –quantitative or qualitative in nature. –Key elements: planning and scoping, identify acute hazards, evaluate health effects, assess exposures & characterize risks.Ecological risk assessment•Evaluate the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors. –Systematically evaluate and organize data, information, assumptions, and uncertainties in order to help understand and predict the relationships between stressors and ecological effects in a way that is useful for environmental decision making. –Key elements: planning and scoping, problem formulation, evaluating toxicity/health effects, assess exposures and characterize risks.Important Differences Between Microbial & Chemical Risks: the Chemical•Unique and specific structures that define (predict) activities•Many molecules may be neded for an effect; gradation of effects•Do not multiply/reproduce•No secondary spread•Accumulation and compartmentalization•Metabolism and chemical reactivity•Detoxification•Threshold (no adverse effect level)•Cumulative effects•Magnitude of exposure influences magnitude of adverse effects and their appearance/manifestation•Distinctive health effects based on chemical reactions with specific molecules, tissues and organs; Structure-Activity Relationships (SAR)Important Differences Between Microbial & Chemical Risks: The Microbial•A single microbe (one unit) is infectious and can cause dramatic effects; magnitude of effects not always related to exposure level•Microbes multiply in a host (increases adverse effects)–Can spread to different compartments (organs & tissues) in host•Microbes multiply in environmental media (some microbes)•Microbes are capable of secondary spread–Can first infect a host from an environmental route of exposure (water, food, etc.)–Can then spread to other hosts by person-to-person transmission•Some microbes cause a wide range (spectrum) of adverse effects•Microbes can change: mutate, evolve, adapt, change gene expression, etc.Quantitative Microbial Risk AssessmentDefinition:Applications of the principles of risk assessment to the estimation of the consequences from anticipated or actual exposure to infectious microorganismsRationale for its emphasis:Most of the disease burden associated with lack of access to or deficiencies in water, sanitation and hygiene is from infectious agents (microbes)Exposure, Level of Protection and Microbial Risk: The RelationshipRisk Exposure Level of Protection (e.g., technologic control)=
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