Epidemiological studies
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Case–control studies (including systematic review)
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Able to identify variety of risk factors, including exposure routes, predisposing, behavioural or seasonal factors
A systematic review of published studies can be useful for regional analysis and may detect temporal and geographical variations
Can identify a wide range of known and unknown risk factors
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Analysis of data from outbreaks
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Documentation that a hazard was transmitted to humans via a specific food item can be available
Data may capture the effect of contamination at multiple points from the farm‐to‐consumption chain
Wide variety of foods represented, including uncommon foods
Most readily available information for source attribution in some countries or regions
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Quality of evidence varies
Large outbreaks, outbreaks associated with point sources, outbreaks with short incubation periods, or more severe symptoms are more likely to be investigated
Investigated cases may not be representative of all food‐borne illnesses
Certain pathogens and foods are more likely to be associated with reported outbreaks, which can lead to an overestimation of the attribution proportion
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Subtyping
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Limited to hazards heterogeneously distributed among the reservoirs
No information on transmission pathways from reservoirs to humans
Data intensive, requiring a collection of representative isolates from all (major) sources
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Comparative Risk Assessment
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Expert knowledge elicitations
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Allows for attribution to main transmission routes
Useful tool when data is lacking
May be the only available method for source attribution
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