Human Health Issues related to Avian Influenza in Canada
This section is intended to clarify some of the terminology that is included in this document.
A national case definition is needed to assist with the identification of affected individuals, the assessment of human health risks and the direction of public health and surveillance activities. National case definitions allow for common and consistent communication both nationally and internationally and as an integral part of surveillance, they help to inform the pandemic phase.
The process for developing a specific national case definition relies on the clinical presentation and laboratory techniques that are associated with identifying the illness. The identified clinical presentation can change as more epidemiologic information becomes available and this may require an update to the case definition.
National definitions that include categories for confirmed cases, suspect cases and asymptomatic or atypical infections are preferred. The latter two categories can assist with the management and investigation of potential cases and be a place holder should the confirmed case definition be updated to include some of the asymptomatic or atypical infections.
Since the case definitions are meant to be used nationally, their development should be through consensus and in collaboration with the federal, provincial and territorial working group that has been developed to assist with issues surrounding national surveillance. Currently, this working group is named the Vaccine Preventable and Respiratory Infections Surveillance Working Group (VPRIS).
The case definitions used in the 2004 avian influenza H7N3 outbreak in British Columbia and the WHO confirmed case definitions for avian influenza H5 can be found in appendix A and B respectively. If an outbreak occurs and it is known to be a H7 or H5 strain, then the case definitions in the appendices can serve as initial national case definitions. They can be adapted for the specific outbreak situation by the province or territory involved in the outbreak in collaboration with the VPRIS and the Public Health Agency of Canada as necessary.
Sources of avian influenza virus:
There is relatively limited public health experience with avian influenza outbreaks and variability has been observed in the epidemiology of avian influenza outbreaks caused by different strains. Therefore, it may be necessary to modify the list of sources of avian influenza virus as the outbreak progresses, more information becomes available, or the situation changes (e.g. if there is evidence of airborne spread of the virus from an avian source).
Potential sources include:
- infected poultry
- under- or uncooked products from infected birds,
- infected wild or pet birds,
- other infected animals (e.g. pigs)
- manure and litter containing high concentrations of virus,
- contaminated surfaces,
- contaminated vehicles, equipment, clothing and footwear at involved sites (e.g., infected poultry farms),
- Contaminated air space (e.g. a barn when movement of birds or manure may have resulted in aerosolization of the virus), OR
- Individuals known to be infected with an avian influenza virus
Note: For outbreak control purposes a flock, location (e.g. farm), or an ill individual with a history of exposure to an avian source of virus, might be considered a "potential source of avian influenza virus" on epidemiological grounds in the absence of confirmed infection.
Contact - avian/animal source
An asymptomatic individual who has been in direct contact with an avian source or potential avian source of avian influenza virus (see list above). (i.e., this excludes individuals whose only exposure was to another individual known to be infected with an avian influenza virus.)
Note: For surveillance purposes, if this individual develops symptoms and meets the case definition they would be referred to as a "primary case". However, if the individual develops a confirmed infection but is asymptomatic or atypical in clinical presentation, they would be considered to have a "primary infection".
Contact - human source
An asymptomatic individual who has been in close contact with an individual known to be or suspected to be infected with an avian influenza virus.
Note: For surveillance purposes, if this individual develops symptoms and meets the case definition they would be referred to as a "secondary case". However, if the individual develops a confirmed infection but is asymptomatic or atypical in clinical presentation, they would be considered to have a "secondary infection".
Any site at which:
- avian influenza has been laboratory confirmed in one or more birds in a poultry flock,
- a higher than normal rate of morbidity or mortality consistent with avian influenza has been observed in one or more flocks,
- a highly pathogenic avian influenza strain has been laboratory confirmed in one or more wild birds.
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