Gertjan Medema Quantitative Microbial Risk Assessment ... - TU Delft

OutlineWhat is QMRA?QMRA frameworkCase studyRelation QMRA – risk management2

Quantitative Microbial Risk Assessment3

Quantitative Microbial Risk Assessment4

Quantitative Microbial Risk AssessmentProbability of hazardous event x adverse effect of event5

Quantitative Microbial Risk AssessmentProbability of hazardous event x adverse effect of event6

Risk assessment7

Risk assessment8

Quantitative Microbial RiskAssessmentProbability of hazardous event x adverse effect ofevent9

Quantitative Microbial Risk AssessmentProbability of hazardous event x adverse effect of event10

Quantitative risk assessment11

Quantitative Microbial Risk AssessmentProbability of exposure to pathogens x health effect of exposure12

OutlineWhat is QMRA?QMRA frameworkCase studyRelation QMRA – risk management13

ILSI Framework for QMRA14

ILSI QMRA FrameworkProblem formulationAnalysis• Exposureassessment• Effect assessmentRisk characterization15

ILSI QMRA FrameworkProblem formulationAnalysis• Exposureassessment• Effect assessmentRisk characterization16

Problem formulationInteraction risk manager – risk assesserDefine the purpose of the QMRADefine the breadth of the QMRAExplore the context of the QMRADevelop a conceptual model• Route(s) of exposure for QMRA• System under evaluation• Pathogens (characteristics)• Exposed population; immunity• Health outcome• Data needs• Preliminar, exploratory assessmentIncorporate control alternatives (optional)17

ILSI QMRA FrameworkProblem formulationAnalysis• Exposureassessment• Effect assessmentRisk characterization18

Analysis - Exposure assessmentPathogen characterisation (relevant for exposure)• Die-off rate• Removal rate• Inactivation rate• Growth ratesPathogen occurrence• Frequency• Concentrations• Seasonality• Methodological issuesPathogen behaviour in system• Removal/inactivation• System variability19

Analysis - Exposure assessment 2Exposure analysis• Calculation of pathogen concentration in matrix• Consumption data• Combination of all information into exposuredata• Include variability (ranges, probabilistic)• Include uncertainty analysis• Include sensitivity analyis20

Analysis – Effect assessmentHost characterization• Age, pregnancy, immune-status, nutritional status etc.Human health effects• Duration• Severity (morbidity, mortality, sequellae)• Secondary transmissionDose response• Human (or animal) dose-response data• Type of response: infection, morbidity, mortality, DALY’s• Inoculum used (type, preparation, administration)• Study population characteristics• Strain variation• Statistical model21

Analysis – Effect assessment 2Host pathogen profile• Include variability• Include sensitivity analysis22

ILSI QMRA FrameworkProblem formulationAnalysis• Exposureassessment• Effect assessmentRisk characterization23

Risk characterizationRisk characterization• Combine data from exposure assessment and effectassessment into characterization of risk• Include variability (probabilistic)• Discuss assumptions: include sensitivity analysis• Discuss how outcome answers problem formulation• (Compare control scenario’s)• Identify data needs/improvements24

QMRA is iterative proces25

OutlineWhat is QMRA?QMRA frameworkCase studyRelation QMRA – risk management26

Case studySetting priorities for risk managementRisk assessment by J.F. Loret27

Problem formulationSuez Environnement operates >1700 water systems in France. After thewaterborne outbreaks of cryptosporidiosis reported in the USA and UK, Suezwanted to develop an approach to evaluate the risk of Cryptosporidium for eachwater system. Such an approach would allow Suez to:• demonstrate compliance with the EU drinking water directive;• know if any of these systems was at risk to Cryptosporidium;• prioritise investments (if needed).Specific risk assessment goalWhat is the risk of Cryptosporidium in the (>1700) water systems?28

Hazard identificationCryptosporidium• absence of specific therapy• resistance to chemical disinfection.Questionnaire operators of each system• volume of water produced,• the type of source water used, including information on the type ofenvironment (urban, rural, presence of cattle etc.)• and data on general water quality parameters (coliforms, turbidity,ammonium and nitrate), and about the type of treatment processes.• The returned information covered treatment facilities that supply 9 millionpeople with drinking water.29

Exposure assessmentCryptosporidium occurrence in source water (data)30

Exposure assessment 2Cryptosporidium occurrence in source water (classes)31

Exposure assessment 3Cryptosporidium removal by water treatment (literature data)32

Effect assessmentDose response data and model (literature)33

Risk characterization34

Risk managementSystems at risk: small (

Case study 2:Water reuse guidelines Australia36

Problem formulationWater reuse guidelines AustraliaSemi-arid to aridIncreasing water demandWater recycling in crop and landscape irrigation,gardeningWater recycling in dual water systems for toiletflushing, laundrySpecific risk assessment questionIs a wastewater recycling system able to meetthe health-based target of 10 -6 DALY / y?37

Hazard identificationWater reuse guidelines AustraliaWastewater may contain a wide range of pathogensQMRA for each is not feasibleSelection of reference pathogens• Parasites: Cryptosporidium (small, resistant, infectious)• Viruses: Adenovirus/Rotavirus (infectious, available data)• Bacteria: Campylobacter (very prevalent, infectious)38

Risk assessmentWater reuse guidelines Australia[Pathogen]wastewaterApplicationSystem performancerequirementsHealth target39

Risk assessmentWater reuse guidelines Australia[Campylobacter]Wastewater7000/LApplicationSystem performancerequirementsHealth target

Risk assessmentWater reuse guidelines Australia[Campylobacter]Wastewater7000/LApplicationSystem performancerequirementsAnnual dose

Exposure assessmentWater reuse guidelines AustraliaConcentration of reference pathogens in wastewaterExposure through various applications42

Risk assessmentWater reuse guidelines Australia[Campylobacter]Wastewater7000/LApplicationSystem performancerequirementsAnnual dose

Risk assessmentWater reuse guidelines Australia[Campylobacter]Wastewater7000/LCommercial crop irrigationSystem performancerequirements5.0 logAnnual dose

Conclusions from case study 2Water reuse guidelines AustraliaQMRA used in wastewater reuse guidelines in aridregion….… to set performance targets for reuse systems… that are application specific… based on a predefined health target… using exposure data from scientific literature45

OutlineWhat is QMRA?QMRA frameworkCase studyRelation QMRA – risk management46

Relation with risk managementHEALTHTARGETSAcceptableriskRiskManagementAssessEnvironmentalExposureAssessmentof riskPUBLICHEALTHSTATUSFrom: Fewtrell & Bartram, 2001. in Water Quality Guidelines, Standards and Health (WHO). IWA publishing.47

Risk managementHACCP / Water safety planAssemble teamHEALTHTARGETReviewingexperience,future needsSystemassessmentDescribe water supplyConduct hazard analysisIdentify Control MeasuresOperationalmonitoringDefine Operational LimitsEstablish monitoringSupportingprogrammesAssessmentofRiskReview,Approvaland AuditManagement &communicationEstablish corrective actionsEstablish record keepingEstablish validation + verificationPUBLICHEALTHSTATUS48

Risk management questions that need quantitative answersRisk management questions thatneed quantification:Assemble teamSystemassessmentDescribe water supplyConduct hazard analysisWhat is my health target?What are the priority hazards?What is the significance of hazardousevents?Identify Control MeasuresIs my overall treatment adequate toproduce drinking water that meets thehealth target?OperationalmonitoringDefine Operational LimitsEstablish monitoringWhat are appropriate critical limits?How much monitoring is necessary?Management &communicationEstablish corrective actionsEstablish record keepingEstablish validation + verificationWhat level of corrective actions isneeded?49

Risk management: balancing the risksExpert judgementRisk 1 Risk 250

Risk management:balance between consumer safety and (consumer)cost.Expert judgementSafetyCosts51

Risk management:balance between consumer safety and (consumer)cost.QMRASafetyQMRACosts52

The value of Quantitative Risk AssessmentThe Commission needs to find the balance betweenthe freedom and rights of individuals, industry andorganisations with the need to reduce the risk ofadverse effects to human health and the environment.This balance should be:• science-based,• proportionate,• non-discriminatory,• transparent,• coherent and• requires a structured decision-making process withdetailed scientific, objective information within anoverall framework of risk analysis.Address by D. Byrne (Commissioner for Health & Consumer Safety) on the PrecautionaryPrinciple in the domain of human health and food safety. The Economist conference, Nov. 9,2000, Paris.QMRA53

Take home messages54

Framework for QMRAHelp the risk managerDefine goal and scope carefully, together with risk manager(s)Good QMRA Practice• Tracebility of data• Include variability (also include the odd peak event)• Describe and test assumptions (sensitivity analysis)Present outcome to risk managerYou are not the risk manager55

QMRA is iterative proces56

Relation with risk managementThere is so much uncertainty….HEALTHTARGETSZero uncertainty does not existAcceptableriskThe uncertainty is there, QMRA makes it visibleRiskManagementAssessEnvironmentalExposure• Weak spots → research programAssessmentof riskRisk management has learned to deal withuncertaintyPUBLICHEALTHSTATUSFrom: Fewtrell & Bartram, 2001. in Water Quality Guidelines, Standards and Health (WHO). IWA publishing.57