Evaluate potential limitations with current foodborne illness source

attribution estimates obtained from outbreak reports.

Neal Golden, Ph.D. January 31st, 2012

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Overview

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Definitions Purpose Background Project Description Illustrative Examples Summary Timeline

Definitions Outbreak

Cases of illness that share a common cause - any two or more cases of illness that are connected to a known common cause FDOSS - Foodborne Disease Outbreak Surveillance System

Sporadic illness An isolated case of illness - when someone becomes ill and

there is no known connection to another person’s illness FoodNet - Foodborne Diseases Active Surveillance Network LEDS - Laboratory-based Enteric Disease Surveillance

system (replaced PHLIS)

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Purpose

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The purpose of this project is to: Assess degree of confidence in the use of outbreak

data to estimate foodborne illness source attribution

Assist in developing criteria that prioritizes pathogens for which outbreak data may be sufficient

Contribute to an analysis of uncertainty The purpose is not to estimate foodborne illness

source attribution

Background

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Source attribution generally requires two key pieces of illness information: 1. the pathogen that caused

the illness, and 2. the contaminated food at

the point of consumption Sporadic illness data, such as FoodNet, and outbreak data,

FDOSS, provide the pathogen, but only outbreak data, provides both the pathogen and the implicated food

So what is the problem of focusing on outbreaks only? FDOSS (outbreaks) is an overall 5% of known confirmed illnesses Therefore, the food source is implicated for only a small fraction

of known illnesses

Outbreaks represent a fraction of total illnesses

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When calculating a source attribution figure by using outbreak data, we need to assume exposure pathways are similar to those that led to sporadic illnesses

Is this a valid assumption?

Numbers above bars represent the number of sporadic illnesses observed for each observed outbreak illness

Is foodborne illness source attribution derived from outbreaks representative of sporadic illnesses?

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Very difficult to answer the above question! Ideally we would have a representative set of cases of sporadic

illness that we know were caused by exposure to specific contaminated foods

However, this is not the case

Therefore, a major source of uncertainty is The validity of the assumption that the distribution of

pathogens and their implicated food vehicles in outbreak reports reflects the relevant foodborne pathways of exposure in the general population

Project Description - General Evaluate similarities in the distributions of outbreak data vs.

sporadic illnesses data for the following four pathogens: Salmonella spp., E. coli O157:H7, Campylobacter spp., and Listeria monocytogenes

If outbreak cases look like sporadic cases across an array of epidemiologically factors, the suggests that the causal exposure pathways are similar in identity and degree of incidence

The workgroup is considering the following comparisons:

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Project Description - Limitations

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Data limited by the FDOSS database given fewer outbreak cases identified compared with lab-based surveillance (sporadic illnesses)

Lack of variables for few direct comparisons National (FDOSS) vs. Regional (FoodNet)

FDOSS outbreaks are national however, FoodNet is composed of 10 states representing about 15% of the U.S. population

LEDS is nationally representative, but passive lab-based surveillance

Illustrative Examples

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Illustrative Examples – Temporal

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Databases compared Outbreak illnesses

FDOSS Sporadic illnesses

FoodNet (active lab-based surveillance) Etiology

Salmonella Data years

1998 to 2009

Comparison of Salmonella outbreak (FDOSS) and sporadic (FoodNet) illnesses by month

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Comparison of Salmonella outbreak (FDOSS) and sporadic (FoodNet) illnesses by year

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vertical line - year FoodNet catchment stabilized

Illustrative Examples – Gender

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Databases compared Outbreak illnesses

FDOSS Sporadic illnesses

FoodNet (active lab-based surveillance) Etiology

Salmonella Data years

1998 to 2009

Comparison of Salmonella outbreak and sporadic illnesses by gender

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Some year-to-year variability

Averaging suggests the fraction of female outbreak cases is very similar to the fraction of female sporadic cases Outbreak: 51.7% Sporadics: 51.5%

vertical line - year FoodNet catchment stabilized

Evaluate potential limitations with current foodborne illness source attribution Timeline

Project plan approved in Fall 2011 Databases have been acquired Following comparisons of the six epidemiologic

factors for the four pathogens, determine if additional analyses are required, Winter 2012

Project completion in Spring 2012

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