Priority Setting for Food Borne Pathogens

Angela Vargas

Supervisors:Dr. Arie Havelaar 

Prof. Dr. Roger Cooke

12, June 2007TU Delft

Overview

• Introduction• Problem Description• Methodology• Paired Comparisons• Probabilistic Inversion• Elicitation and Analysis• Results• Conclusions and Recommendations

Introduction

Disease Burden

YLD Years Lived with a Disability

YLL Years of Live Lost

DALY Disability-Adjusted Life Years

Cost-of-illness

COI Cost-of-illness

DHC Direct Health care Costs

DNHC Direct Non-health care Costs

INHC Indirect Non-health care Costs

Fraction of cases attributable to Food

Fraction of cases attributable to Food Group

Pathways

Pathways

Food borne Environmental Human-human Direct animal Traveling

Food borneTransmission through food that is contaminated when it enters the kitchen or during preparation (e.g. by food handlers).

EnvironmentalTransmission through contaminated water (drinking water, recreational water), soil, air or other environmental media.

Human-human Transmission from person to person by the fecal-oral route.

Direct animalTransmission by direct contact with live animals including pets, farm animals, petting zoos etc.

AbroadCases when exposure takes place by any of the above pathways during foreign travel.

Pathways Description

Food

Categories

Beef and lamb

Pork

Chicken and other poultry

EggsDairy products

Fish and shellfish

Fruit and vegetables

Beverages

Bread, grains, pastas and bakery products

Other foods incl. composite foods

Infected humans or animals

Food Categories

Problem Description

• Determine the fraction of transmission route for each pathogen and the fraction of transmission due to specific food groups.

•The objective is to find a fast, not resource intensive and accurate method of estimation for these fractions.

• Estimated fractions that will sum to one

• Insufficient data

Methodology

Paired Comparisons

• Compare pair wise of all items in order to determine preference.• The result is a score for each item.• Lighter elicitation for experts.• The resulting scores sum to one.

Probabilistic Inversion

• Experts give quantiles for the query variables. • It is possible to estimate results that sum up to one. • …

Paired Comparisons

 10000  0001 1 11110 01 101 

Paired Comparisons Results

Item name Score Conf L. Conf U.

Food Ingestion 0.9557 0.8335 0.9978

Environment 0.0123 0.0003 0.0528

Contact with sick person

0.0015 0.0000 0.0054

Direct animal contact

0.0046 0.0001 0.0145

Contamination abroad

0.0259 0.0010 0.1058Pairec Comparisons Results for Pathways Salmonella

0.9557

0.0259

0.0046

0.0123

0.0015

Food Ingestion

Environment

Contact with sick person

Direct animal contact

Contamination abroad

Paired Comparisons Results

Item name Score Conf L. Conf U.

Beef and lamb0.052

40.0189 0.1079

Pork0.160

10.0632 0.2745

Chicken and poultry

0.2909

0.1619 0.4658

Eggs0.449

20.2756 0.6481

Dairy products0.009

80.0016 0.0211

Fish and shellfish0.006

90.0012 0.0163

Fruit and vegetables

0.0061

0.0013 0.0148

Beverages0.001

20.0001 0.0029

Bread, grains, pasta

0.0023

0.0003 0.0049

Composite Foods0.011

80.0026 0.0251

Food Handlers0.009

30.0015 0.0195

Paired Comparisons Results for Food Categories Salmonella

0.1601

0.2909

0.4492

0.0093

0.05240.0069

0.0098

0.0012 0.01180.0023

0.0061Beef and lamb

Pork

Chicken

Eggs

Dairy

Fish

F & V

Beverages

Bread, grains

Composite

Food Handlers

Probabilistic Inversion

BACK

u1 u2

0.11 0.89

0.19 0.81

0.83 0.17

0.12 0.88

0.31 0.69

0.11 0.89

0.73 0.27

0.59 0.41

0.77 0.23

0.94 0.06

0.73 0.27

0.15 0.85

1

1

1

1

1

1

1

1

1

1

1

1

00.160.15

0.130.220.12

0.100.140

0.31

0.46

0.24

0.220.510.26

IPF – One iteration

0 0.25 0.02

0.02 0.38 0.03

0.03 0.27 0

1 2 3

,

,

( ) 0.05 0.9 0.05

jj

iji

ii

ijj

p p p p

Column j

pa

a

Row i

pa

a

0.05 0.9 0.05

0.268

0.430

0.302

0 0.046 0.004

0.05 0.79 0.06

0.004 0.045 0

0.050

0.900

0.050

0.05 0.89 0.06

00.160.15

0.130.220.12

0.100.140

0.31

0.46

0.24

0.220.510.26

Re-Sampling

0 0.047 0.003

0.045 0.808 0.047

0.005 0.045 0

0.05

0.9

0.05

0.05 0.9 0.05

w1

w2

w3

w4

w5

w6

w7

w8

…

W n

Re- sample

Elicitation and Analysis

Specify an interval which contains the probability of occurrence with 90% certainty.

A case of illness due to Bacillus cereus toxin was transmitted by ingestion of Pork:

≤ 100% ≤0% ≤

16 experts participated in the elicitation.

Results

“Seed Variables”

Some probabilities are believed to be zero therefore that value was used as the true value and used as a seed variable.

Additionally 50%

Fit was done based on the 5%, 50% and 95% quantile of the equal weight distribution

5% and 95% Fit was done based on the 5% and 95% quantile of the equal weight distribution

Issues

Data Recollection• Finding the experts. Encouraging them to participate and actually answer.• No opportunity to give them guidance• Number of experts per pathogen

Validation• How to evaluate the quality of the estimates

Results

QUESTIONS

Expert 27

Food Salmonella

0% 20% 40% 60% 80% 100%

E3 E9 E11 E12 E22 E27 E33 E36 E37Equal W.

Food Salmonella w ithout expert 27

0% 20% 40% 60% 80% 100%

E3 E9 E11 E12 E22 E33 E36 E37Equal W.

Environment Salmonella

0% 20% 40% 60% 80% 100%

E3 E9 E11 E12 E22 E27 E33 E36 E37Equal W.

Environment Salmonella w ithout expert 27

0% 20% 40% 60% 80% 100%

E3 E9 E11

E12 E22 E33

E36 E37Equal W.

Expert 27

Sick Salmonella

0% 20% 40% 60% 80% 100%

E3 E9 E11 E12 E22 E27 E33 E36 E37Equal W.

Amimal Salmonella

0% 20% 40% 60% 80% 100%

E3 E9 E11 E12 E22 E27 E33 E36 E37Equal W.

Sick Salmonella w ithout expert 27

0% 20% 40% 60% 80% 100%

E3 E9

E11 E12

E22 E33 E36

E37Equal W.

Amimal Salmonella w ithout expert 27

0% 20% 40% 60% 80% 100%

E3

E9 E11

E12

E22 E33

E36

E37Equal W.

Abroad Salmonella

0% 20% 40% 60% 80% 100%

E3

E9

E11

E12

E22 E27

E33

E36

E37

Equal W.

Abroad Salmonella without expert 27

0% 20% 40% 60% 80% 100%

E3

E9

E11

E12

E22

E33

E36

E37

Equal W.

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