Source Attribution

Focus on sources and pathogens

Infectious enteric disease is caused by a broad spectrum of pathogens that can reach humans by multiple paths (e.g. water, food, animals, other persons). Consequently, the surveillance of enteric diseases in Canada must be comprehensive. C-EnterNet has developed its surveillance framework accordingly. Program specifications include simultaneous investigation of all viral, bacterial and parasitic transmission routes. In addition, sample collection is active and systematic, laboratory analysis is in-depth, and results are reported to stakeholders by effective and timely communications. Furthermore, the increased volume and quality of epidemiological data provided through C-EnterNet's planned network of up to five sentinel sites will help in developing improved methods for source attribution, thus providing new insight into the risks present in pathogen exposure routes. This comprehensive sentinel site surveillance, implemented through partnerships with local public health units, will generate accurate data to inform the evaluation and development of food and water safety policies and programs in Canada .

C-EnterNet will focus on the pathogens known to have the greatest potential to cause enteric diseases in Canada , with particularly severe consequences for the youngest, oldest and immune-compromised members of the population.

Check chart for latest changes and consistency with all other pieces

Pathogen	Public Health	Water	Agriculture	Retail Food
Salmonella	Y	Y	Y	Y
E. coli (VTEC)	Y†	Y	Y†	Y
Campylobacter	Y	Y	Y	Y
Yersinia	Y	Y	Y*	Y*
Listeria	Y		Y	Y
Shigella	Y
Vibrio	Y
Cryptosporidium	Y	Y	Y	Y
Cyclospora	Y			Y
Giardia	Y	Y	Y	Y
Norovirus	Y		Y	Y
Rotavirus	Y		Y	Y
* Yersinia will be tested in swine and raw pork samples only. † E. coli O157:H7 will be tested in the human and agricultural samples only.

Pathogens from each source (water, retail food or agriculture) are subjected to the same standardized microbiological analyses and sub-typing. This provides C-EnterNet with the ability to determine current levels of enteric pathogens in each source, as well as the ability to monitor changes over time. These analyses will provide benchmarks for measuring interventions, future initiatives and policy development related to food and water safety in Canada .

Methodological options

In an era of highly dynamic pathogens, increased international trade, travel, urbanization and global warming, several scientific methods of source attribution have been developed, including

• outbreak data analysis;
• comparison of the pathogen profiles of the [human] population and of various sources of exposure (also known as microbial source tracking);
• case control studies, where exposures of sick and healthy individuals are compared; and
• quantitative risk assessment.

At present, none of these methods is sufficiently accurate on its own, which makes it difficult to address infectious enteric diseases at their sources. Recognizing that more accurate source attribution is vital to a comprehensive surveillance program and to better identification, control and response with regard to infectious enteric disease outbreaks, C-EnterNet has evaluated the potential of each existing methodology. The continuous search for greater accuracy will include work with collaborators to build on those methodologies that are most scientifically promising and most relevant.

C-EnterNet will approach source attribution mainly through the comparison of pathogen profiles (microbial source tracking). It is currently the most promising method, because of the rigor and specificity of the microbiological analysis and its potential for producing reliable data. In addition, C-EnterNet will have the microbial data necessary to monitor trends over time in both the population and the sources of exposure. To complement the pathogen profiles and to achieve greater accuracy, C-EnterNet will also use outbreak data analysis, because its data results are immediately available for both the sentinel site and for all of Canada . To address very specific questions, C-EnterNet may implement case control studies, or develop quantitative risk assessment models as part of its episodic surveillance activities.

Unique benefits

Improved source attribution will help determine, with greater certainty, the most important sources and pathways of each pathogen that causes infectious enteric disease. This precise information will help focus, in the most cost-effective manner, resources allocated to food and water safety and communicable disease prevention, in order to reduce the burden of enteric disease in Canada.