Source Attribution

Definition and Purpose

Human illness attribution (source attribution) of infectious enteric diseases is one of the key scientific objectives of the FoodNet Canada system (formerly known as C-EnterNet).

Infectious enteric disease can be caused by any of a wide variety of germs: viral, bacterial, or parasitic. People get sick from these germs through contaminated food or water or by contact with other sick people or animals.

Food-borne source attribution is the partitioning of the human disease burden of one or more food-borne infections to specific sources, where the term “source” includes animal reservoirs and vehicles (e.g., foods) (Pires et al., Food-borne Pathogens and Disease, 2009, 6(4): 417-424).

FoodNet Canada uses a broader and more specific definition: The partitioning of the human infectious gastrointestinal illness to specific sources, where the term “source” includes animal reservoirs and vehicles (i.e., encompassing all food-borne, water-borne, animal-to-person, and person-to-person transmission routes relevant to the illness epidemiology of gastrointestinal illness).

In source attribution, the “source” includes both the reservoir of the pathogen or the vehicle. The reservoirs are hosts from which the pathogens originate, which can include diseased and asymptomatic carriers/shedders among human beings, and ill and carrier animals (food animals, pets, wildlife; the former being often referred to as the point-of-production source). The vehicles facilitate contact between pathogen reservoirs and people. These vehicles can include water, food, animals, soil, manure, compost, and other persons.

Source attribution for gastrointestinal illness helps us look at each of the many combinations of factors that can cause illness and, for each, estimate:

As a result, source attribution has become an important tool to better inform food and water safety policy development and evaluation. Ultimately, source attribution helps to decrease the burden of enteric disease in Canada. It also helps us evaluate whether new policies and interventions on the farm, in the environment, or in food production are effectively decreasing disease in Canada.

Methodological approaches

Several methods are available that can be used to estimate the source and burden for the human illnesses caused by enteric diseases (Pires et al., 2009). Each method has specific strengths and limitations. Experts on source attribution have concluded that none of the currently available methods are able to give an accurate estimate for source attribution on their own. These approaches are quite different in concept and in scope and address slightly different questions; thus their results are considered more complementary than comparable.

Evidence Generated by FoodNet Canada

Since 2005,FoodNet Canada researched and developed several products using various source attribution methods in Canada. These include:

Finally, because all approaches yield results that are more complementary than comparable, efforts are being made to synthesize the results from the various studies undertaken in Canada.

Improved source attribution will help determine, with greater certainty, the most important sources and pathways of each pathogen that cause infectious enteric disease. This information will help focus resources allocated to food and water safety and communicable disease prevention in the most cost-effective manner, in order to reduce the burden of enteric disease in Canada. It also will provide Canada with the ability to evaluate the effectiveness of interventions at the farm, processing, and environment levels to improve food and water safety and public health.

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