Risk Assessment Guest Lecture

1
Risk AssessmentGuest Lecture

• Thomas P. Oscar, Ph.D.
• USDA, ARS
• Princess Anne, MD

2
Risk AssessmentHolistic Approach to Food Safety

• Hazard Identification

• Hazard Characterization

Disease Triangle

• Exposure Assessment

• Risk Characterization

3
Hazard Identification

• Epidemiological data
• Outbreaks
• Sporadic cases
• End product testing
• Pathogen number and distribution in food

Higher risk food/pathogen combos
Expensive time consuming
4
Exposure AssessmentChange in pathogen
distribution and number from hazard
identification to the table

• Unit Operations
• Retail Store
• Consumer Transport
• Cooking
• Serving
• Consumption

• Pathogen Events
• Contamination
• Growth
• Death
• Cross-contamination
• Dose-response

5
Hazard CharacterizationIndividual Dose-response
Disease Triangle
6
Hazard CharacterizationPopulation Dose-response
Disease Triangle
Uniform Pathogen Food Host
7
Hazard CharacterizationPopulation Dose-response
Disease Triangle
Non-uniform Pathogen Food Host
8
Risk CharacterizationPublic Health Impact

• Rate of Illness
• Number per 100,000 consumers

• 15 to 20 cases per 100,000 consumers
• 0.66 to 0.88 cases per 100,000 chicken consumers

9
A Quantitative Risk Assessment Model for
Salmonella and Whole Chickens

• International Journal of Food Microbiology, 2004
• vol. 93231-247.

10
Quantitative Risk Assessment Model (QRAM)
Fig. 1
11
Monte Carlo Simulation
Incidence
Extent

• Input Distributions
• Random Number Generator
• Formula
• A 2B2 C
• Output Distributions

A B C
1 6 7 104
2 3 5 53
3 8 2 16

100 2 9 164
12
Pathogen Eventsgrowth, death, survival,
cross-contamination

• Rare

• Random

• Variable

• Uncertain

13
Rare Events ModelingInitial Contamination
Iteration 1 2 3 100
Discrete 1 0 0 0
Pert (0,1,4) 1.8 1.2 0.2 2.2
Power 63.1 15.8 1.6 158.5
Round 63 0 0 0
RiskDiscrete(90,10,0,1) RiskPert(0,1,4) Po
wer(10,Pert) Round(IF(Discrete0,0,Pert),0)
14
Node 1RetailInitial Contamination
Extent (log MPN/chicken) Extent (log MPN/chicken) Extent (log MPN/chicken)
Incidence Minimum Median Maximum
30 0 1 2.7
15
Probability DistributionIncidence
16
Probability DistributionLog Number
17
Node 2Consumer Transport Growth
Extent (log change/chicken) Extent (log change/chicken) Extent (log change/chicken)
Incidence Minimum Median Maximum
0.02 0.0005 0.04 0.15
Time (0.2, 1, 6.3 h)
Predictive Model (Oscar, 2002)
Consumer survey
Temp (-3.9, 7.8, 21.1?C)
18
Node 3CookingThermal Inactivation
Extent (log change/chicken) Extent (log change/chicken) Extent (log change/chicken)
Incidence Minimum Median Maximum
100 -96 -8.1 -0.83
Time (15,30,45 min)
Predictive Model (Murphy et al., 2002)
Consumer survey
Temp 55,62,70?C)
Fig. 2
19
Probability DistributionLog Cycle Change
20
Node 4ServingCross-contamination
Extent ( transfer/chicken) Extent ( transfer/chicken) Extent ( transfer/chicken)
Incidence Minimum Median Maximum
28 0.021 0.057 0.24
21
Probability Distribution Transfer
22
Node 5ConsumptionDose-Response
Extent (log illness dose) Extent (log illness dose) Extent (log illness dose)
Incidence Minimum Median Maximum
100 1 3 7
If (dose consumed lt illness dose, no illness,
illness)
Disease Triangle
Pathogen
Host
Food
23
Probability DistributionIllness Dose
24
ResultsChicken 6632 of 10,000 simulated
Fig. 3
25
Simulation Results Nodes 1 to 5
Fig. 4
26
Node 2Consumer Transport
Fig. 5
27
Node 3Cooking
Fig. 6
28
Node 4Serving
Fig. 7
29
Node 5Illness Dose
Fig. 8
30
Node 5Dose-response Assessment
Fig. 9
31
Risk Characterization
1 million chickens 4 people ate each chicken
RNGS Cases
1 17
7 21
29 18
83 14
17.8 (1.5)
17.8 cases/1 million chickens or 0.44
cases/100,000 consumers
32
What if ScenariosEfficacy of Interventions
Short-term no change in illness
dose Longer-term 50 or 75 decrease in illness
dose
PR 50 pathogen reduction before retail e.g.
antimicrobial rinse CE 50 pathogen reduction
at serving e.g. consumer education
33
Risk AssessmentHolistic Approach to Food Safety

• Hazard Identification

• Hazard Characterization

• Exposure Assessment

• Risk Characterization