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Quantitative Risk Assessment

Don Schaffner, Ph.D.

Rutgers, The State University of NJ

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Overview

- How does risk analysis relate to risk assessment?

- How is risk assessment applied to food microbiology?

- A very simple example of a quantitative risk assessment

- Web links and more information

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Risk Analysis Components

- (Quantitative) Risk Assessment• How big is the risk, what factors control the risk?• Scientific process

- Risk Communication• How can we talk about the risk with affected

individuals?• Social and psychological process

- Risk Management• What can we do about the risk?• Political process

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Step in Risk Assessment

- Hazard Identification • What microbe, food(s) and people are involved?

- Exposure Analysis • What is the chance of exposure?• How many cells?

- Dose-Response Analysis • What is the human health effect of the exposure?

- Risk Characterization • Complete picture of the assessed risk

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Hazard Identification

- Epidemiological data linking• Foods• Pathogens• Human illness

- Special considerations• Disease complications• Acute vs. chronic disease• Specific sensitive consumer populations• Characteristics of the organism • Organisms mode of action

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Exposure Analysis

- Estimate•likelihood of consumption•likely number (dose) of the

pathogen

- If “quantitative” assessment•Modeling•Simulation

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Exposure - Simple Example

- Initial number of organisms follows a Poisson distribution

- Growth rate is normally distributed

- Product composition and storage temperature are fixed

- The product becomes unsafe when it contains 100,000 organisms/gram

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Initial number - Poisson

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Growth rate is normal

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Simulation Results

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Dose-Response Analysis

•Translates exposure analysis output in to a measure of human health

•If “quantitative”•Use dose-response curve •Estimate probability of infection and illness from dose

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Dose response curve

Cassin et al. Quantitative risk assessment for Escherichia coli O157:H7 in ground beef hamburgers. Int.J.Food Micro. 41 (1):21-44, 1998.

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Dose-Response factors

- Statistical model(s) to analyze or quantify dose- response relationships• Threshold vs. non-threshold models

- Dose response data• Human • Animal• Outbreak or intervention data

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Dose-Response factors

- Source and preparation of challenge material or inoculum

- Organism type and strain• Virulence factors or other measures

of pathogenicity

- Characteristics of the exposed population• Age, immune status, etc.

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Risk Characterization

- Final task in risk assessment

- Combines the information from•Hazard identification•Exposure analysis•Dose-response analysis

- Produces a complete picture of the assessed risk

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A good risk assessment…

- Is… •Transparent•Iterative

- Includes… •Variability and uncertainty•Management input into problem

formulation

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A hot-air balloon floats overhead…

RM: I’m lost, can you tell me where I am?

RA: Sure, you are 30 feet off the ground

RM: Aha, you must be a risk assessor

RA: Why yes, how did you know?

RM: Because what you told me was technically correct, but of absolutely no use.

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A hot-air balloon floats overhead…

RA: Aha, you must be a risk manager?

RM: Why yes, how do you know?

RA: That’s easy, you don’t know where you are, what you want or where you are going… and you are in the same position now as you were before you asked for my help, but now it’s my fault!

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Importance of risk assessment

- Teaching• Students can see “what if...”

- Research• Pinpointing uncertainties or knowledge gaps

- Industry• Optimizing safety while retaining quality

- Government• Designing regulations for the greatest benefit

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For more information

- Annotated bibliography on Food Safety Risk Assessment, Management and Communication• http://www.nal.usda.gov/fnic/foodborne/risk.

htm

- Food Safety Risk Analysis Clearinghouse• http://

www.foodriskclearinghouse.umd.edu/welcome.htm

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For more information

- Revised Framework for Microbial Risk Assessment – ILSI• http://www.ilsi.org/file/mrabook.pdf

- WHO/FAO microbial risk analysis page• http://www.who.int/fsf/mbriskassess/

index.htm

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Software

- USDA Pathogen Modeling• http://www.arserrc.gov

- @risk• http://www.palisade.com/

- Crystal ball• http://www.decisioneering.com/

- Analytica• http://www.lumina.com

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Books

- T. A. McMeekin, et al. Predictive microbiology: Theory and application, Somerset, England:Research Studies Press Ltd., 1993.

- C.H. Haas, et al. Quantitative microbial risk assessment, Ny, NY: John Wiley & Sons, 1999.

- D. Vose. Risk Analysis: A Quantitative Guide, Chichester:John Wiley & Sons, 2000.

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Published risk assessments

- S. enteritidis in eggs• http://www.fsis.usda.gov/OPHS/risk/index.ht

m

- Listeria in RTE foods• http://www.foodsafety.gov/~dms/lmrisk.htm

l

- Fluoroquinolone Resistant Campylobacter in Chicken• http://www.fda.gov/cvm/antimicrobial/

Risk_asses.htm

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Published risk assessments

- Vibrio in shellfish• http://www.cfsan.fda.gov/~dms/vprisk.html

- E.coli O157:H7 in ground beef• http://www.fsis.usda.gov/OPHS/ecolrisk/

home.htm

- Campylobacter in chicken• http://www.who.int/fsf/mbriskassess/

studycourse/annac/index.html

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