Table E.2.

Strengths and limitations of source attribution methods (adapted from Pires et al., 2014)

SA approach	Strengths	Limitations
Epidemiological studies
Case–control studies (including systematic review)	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	Misclassification due to immunity may reduce attributable risk or suggest protection Most studies only explain a small fraction of all cases – Cases may reflect a mixture of possible sources of exposure – Misclassification due to recall bias may lead to an underestimation of the attribution proportion
Analysis of data from outbreaks	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	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
Subtyping	Identifies the most important reservoirs of the hazard, and therefore: a) is useful to prioritise interventions at production level; b) reduces uncertainty due to cross‐contamination or spread to accidental sources	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
Comparative Risk Assessment	Accounts for different transmission routes from the same reservoir Easily updated	Often limited by lack of data, resulting in large uncertainties
Expert knowledge elicitations	Allows for attribution to main transmission routes Useful tool when data is lacking May be the only available method for source attribution	Conclusions are based on the individual expert's judgement, which may be misinformed or biased