Rapid risk assessment: Avian influenza A(H5N1) clade 2.3.4.4b

Assessment completed: June 21, 2023

On this page

• Overall risk statement
• Risk assessment summary
• Future risk in Canada
• Proposed actions for public health authorities and One Health partners
• Disclaimer
• Rapid risk assessment background and methods
• Risk estimate summary
• Limitations
• Knowledge gaps
• Acknowledgements
• Appendix A: Methods
• Appendix B: Occupational and recreational groups with potentially relevant exposures
• References

Overall risk statement

The overall risk to the general population in Canada from avian influenza A(H5N1) clade 2.3.4.4b is low. Those with higher-level exposure to domestic or wild birds or wild mammals are at increased risk of infection.

For the general population in Canada with low level of exposure to birds, human infection with avian influenza A(H5N1) clade 2.3.4.4b acquired from birds (wild birds or commercial or backyard poultry) is very unlikely. For the population with higher level of exposure to birds, infection is unlikely due to the low proportion of birds infected as well as the limited capacity of the virus to infect humans. The uncertainty associated with these estimates varies widely, due to limited information on the infectivity of this clade for humans, limited surveillance and testing in human populations exposed to birds as well as backyard poultry, and gaps in information regarding backyard poultry flocks in Canada.

Infection with avian influenza A(H5N1) clade 2.3.4.4b from mammals is very unlikely for the general population with higher-level exposure to domestic mammals (e.g., dogs and cats) but lower-level exposure to wild mammals. For the population with higher-level exposure to wild mammals (e.g., wild carnivores and scavengers), infection is unlikely due to the low proportion of wild mammals infected and the limited capacity of the virus to infect humans. There is moderate to high uncertainty in these estimates due to limited surveillance and testing of mammalian species and the limited information on the infectivity of this clade for humans.

The impact on the first infected individual(s) in Canada is estimated to be major, considering the severe clinical manifestations seen in some cases globally, as well as the expected burden from control measures, such as isolation and quarantine, on affected individuals and their close contacts. Notably, early detection and prompt treatment in Canada will likely reduce disease severity. Uncertainty in this estimate is high, because of the variability in clinical presentations, ranging from asymptomatic infection to death, among the limited number of reported human detections from other countries to date.

Since there is no evidence that the virus has acquired the capacity for sustained transmission among humans, further human-to-human transmission is not expected. Therefore, the overall impact to the Canadian population would be minor, with low uncertainty.

Risk question

What is the likelihood and impact of at least one human infection with avian influenza A (H5N1) clade 2.3.4.4b due to exposure to either birds or mammals in Canada up to the end of the 2023 fall bird migratory season?

Risk assessment summary

Future risk in Canada

Continued transmission of avian influenza A(H5N1) clade 2.3.4.4b viruses in wild and domestic bird populations, and repeated spill-over into mammalian species, increases the likelihood of viral reassortment and/or adaptation that could enable sustained transmission in wild and/or domestic mammalian species. This may result in increased opportunities for human exposure to these viruses. Although human infections, including fatalities, have been documented in other countries among individuals with exposure to animals infected with avian influenza A(H5N1) clade 2.3.4.4b viruses and possibly virus-contaminated environments, human-to-human transmission has not been reported to date. There is high uncertainty regarding the likelihood of these viruses acquiring mutations that enable sustained human-to-human transmission. A recent multisectoral Pandemic Risk Scenario Analysis led by the Agency determined that the most likely scenario by March 2024 is sustained transmission in non-human mammals, according to majority expert opinion. Sustained human-to-human transmission leading to a pandemic was considered a scientifically credible but less likely scenario.

If sustained human-to-human transmission does occur, the human health impacts will depend on virus transmissibility (the reproduction number); the speed of transmission (epidemic doubling time); the role of asymptomatic and pre-symptomatic virus shedding in transmission; illness severity; individual, health system and societal vulnerabilities; and the effectiveness and availability of countermeasures. There is high uncertainty regarding all of these factors. The course of a human epidemic, were it to occur, is therefore highly uncertain at present, emphasizing the importance of surveillance and preparedness activities in both human and animal sectors.

Even in the absence of widespread community transmission, clusters of disease in high-risk settings such as healthcare institutions could put strain on medical and public health resources for diagnostics, medical treatment and outbreak management, and result in staff shortages through absenteeism if healthcare staff are affected.

Wider transmission in animal populations could also have indirect impacts on human wellbeing and wider society. Increasing outbreaks in farmed animals could have large-scale economic impacts in the agricultural sector from direct losses due to illness as well as outbreak containment measures and international trade implications. The wellbeing of producers and farm employees could also be affected due to animal welfare impacts, loss of livelihood, and disruption of the agricultural sector. Outbreak containment measures could also affect the wellbeing of personnel involved in outbreak response and clean-up and disposal on farms. Shortages in food animal commodities could affect food security in certain sectors of the population. Widespread virus transmission in wildlife populations could also have food security implications in Indigenous communities that rely on wildlife for food. Wildlife population numbers, particularly for at-risk or endangered species, could be impacted, and there could also be impacts on the wellbeing of personnel involved in response and clean-up of wildlife die-offs. Impacts on human wellbeing could also occur from reduced interaction with natural ecosystems, resulting from fear of exposure to infected animals.

Proposed actions for public health authorities and One Health partners

Recommendations proposed below are based on the knowledge gaps identified during this risk assessment. It is important that the public health response be proportionate to the risk, taking into consideration available public health resources and capacity.

PHAC will continue to engage One Health partners (federal, provincial, territorial and other non-government organizations) domestically and collaborate with international partners to assess public health risks associated with current and future avian influenza A strains. The recommendations proposed below are to guide public health actions in the following areas:

Surveillance and reporting

• Continue efforts to further enhance and integrate surveillance activities for avian influenza across the One Health spectrum to,
  • improve understanding of infection and disease burden due to avian influenza A(H5Nx) clade 2.3.4.4b in different animal species, particularly understudied mammalian species;
  • monitor changes in virus evolution and species adaptation as well as antiviral resistance;
  • understand infection risk in human population groups with higher exposure (e.g., backyard poultry, agriculture workers); and
  • rapidly detect and respond to a potential human infection, especially where human-to-human transmission may be occurring.
• Establish enabling mechanisms and structures between animal and human health surveillance systems in Canada for rapid information sharing of case detections, exposure data, genomic analysis including timely clade identification, and other relevant intelligence that can inform the global avian influenza knowledge base.

Communication and coordination

• Continue to foster timely coordinated communication and actively build trust among One Health stakeholders, including counterparts in human, environmental and animal health sectors at local, provincial, regional and federal levels, such that established relationships may be leveraged for harmonized inter-agency pandemic preparedness and outbreak prevention and response activities, including response planning for the first human case(s).
• Continue regular communication with the public on the current avian influenza A(H5N1) clade 2.3.4.4b and share associated guidance related to preventive measures^{Footnote 1}, specifically, for those at potentially higher risk of exposure and infection, including but not limited to farmers/producers and farm workers; hunters/trappers; and those who work with wildlife, stray and feral animals; etc.). When necessary, correct and counter mis- or disinformation.

Research

• Consider discussing and pursuing potential research activities as identified in the Knowledge gaps (Table 5).

Disclaimer

The qualitative and expert-opinion-based methodology is intended to be used in situations where policy decisions need to be made in the face of high uncertainty. The assessment was primarily informed by the team's collective professional knowledge on such topics as infectious diseases, virology, epidemiology, the health system, industry practices, and human-animal interactions. Where appropriate, some references have been provided, but this is not intended as a literature review. The estimates represent the consensual, but not necessarily unanimous, opinions of the participants, and should not be interpreted as representing the views of all participants and their respective organizations.

Rapid risk assessment background and methods

Event background (current situation as of May 30, 2023)

Birds

The avian influenza A(H5N1) clade 2.3.4.4b virus emerged in 2020, spreading across Europe, Asia, and Africa, in both wild birds and domestic poultry, and replaced the previously circulating avian influenza A(H5N8) clade 2.3.4.4b virus in Europe by spring 2021.

The Canadian Food Inspection Agency (CFIA)'s National Centre for Foreign Animal Diseases (NCFAD) first confirmed the avian influenza A(H5N1) clade 2.3.4.4b virus in Canada in December 2021, in a fancy chicken at a small mixed animal exhibition farm in Newfoundland and Labrador.^{Footnote 2} Since then, over 7 million birds from commercial and non-commercial flocks in Canada have been culled as a result of virus containment measures or have died from infection with the virus.^{Footnote 3}

Avian influenza A(H5N1) clade 2.3.4.4b viral activity is unprecedented in terms of the number of wild bird species infected, the extensive geographic spread, and duration of the epizootic.^{Footnote 4} Detection of avian influenza A(H5N1) clade 2.3.4.4b viruses containing the polymerase basic protein 2 (PB2) E627K amino acid substitution, a known marker of mammalian adaptation, has been reported since April 2023 in viruses from some infected poultry farms in Canada (12 in Québec, 1 in Ontario). While this adaptation has been detected in wild birds and birds of prey previously, this is the first time PB2 has been seen in Canadian domestic poultry.^{Footnote 5,Footnote 6}

Non-human mammals

Since October 2020, sporadic avian influenza A(H5N1) and avian influenza A(H5) infections in several wild mammalian species have been reported in Europe and the Americas affecting at least 24 species of carnivores and 4 species of cetaceans. ^{Footnote 7} In March 2023, 10 South American bush dogs in a captive breeding program in England tested positive for avian influenza A(H5N1). All were either dead or euthanized over a 9-day period.^{Footnote 8} They were tested as part of a routine investigation into an unusual mammal die-off in November 2022 and had minimal clinical signs before death.^{Footnote 8} There was no clear evidence suggesting mammal-to-mammal transmission and it is very likely all animals were exposed to the same source of infected wild birds.^{Footnote 8} In Canada, wild mammal species reported to have been infected with avian influenza A(H5N1) clade 2.3.4.4b include, but are not limited to, foxes, skunks, bears, raccoons, seals and dolphins.^{Footnote 4} Avian influenza A(H5N1) has recently been reported in a domestic dog and in feral cats in Ontario. The dog and one cat have been confirmed infected with avian influenza A(H5N1) clade 2.3.4.4b. Additional results are pending.

In an analysis of tissue samples collected from dead or euthanized mesocarnivores in Canada between April to July in 2022,^{Footnote 9} histologic lesions associated with avian influenza A(H5N1) clade 2.3.4.4b viruses were found in several red foxes, indicating extensive meningoencephalitis and pneumonia, as well as abundant virus antigen in the brain sections.^{Footnote 9} Ferret experiments conducted in Canada demonstrated efficient transmission by direct contact of an avian influenza A(H5N1) clade 2.3.4.4 virus (A/Red Tailed Hawk/ON/FAV-0473-4/2022), resulting in lethal outcomes.^{Footnote 10} These ferrets succumbed to infection within one week and showed detectable infectious virus in the brain, consistent with the neurotropism seen in infected foxes.^{Footnote 10}

Following detection of avian influenza A(H5N1) clade 2.3.4.4b in a free-ranging poultry farm in Rome virological and serological investigations were conducted in pigs with no clinical signs on the same premises. Serological samples were positive for avian influenza A(H5N1) and phylogenetic analysis confirmed the virus detected belonged to clade 2.3.4.4b.^{Footnote 11} There are limited reports of potential direct mammal-to-mammal transmission with avian influenza A(H5N1) clade 2.3.4.4b virus. In October 2022, an outbreak occurred on a farm of over 52,000 mink in Spain.^{Footnote 12} Of 15 mink tested, 14 were positive for avian influenza A(H5N1) clade 2.3.4.4b by RT-PCR and the mortality rate on the farm started at 0.8% the first week of October and by the third week reached a peak mortality rate of 4.3%.^{Footnote 12} Based on epidemiological evidence, onward transmission of the virus from mink-to-mink may have taken place on the affected farm.^{Footnote 12}

Large numbers of marine mammals have been infected with avian influenza A(H5N1) clade 2.3.4.4b viruses during the current global epizootic.^{Footnote 13} In an outbreak among New England seals in the United States, transmission is likely to have occurred from wild birds to seals via environmental transmission of shed virus.^{Footnote 14} In January and February 2023, a large sea lion die-off in Peru coincided with an outbreak of avian influenza A(H5N1) clade 2.3.4.4b in seabirds. A report of this event concluded that transmission likely occurred due to close contact with or consumption of infected birds, but direct transmission between sea lions could not be ruled out.^{Footnote 15}

Humans

Since December 2021, detections of avian influenza A(H5N1) clade 2.3.4.4b viruses in humans have been reported from China (n=2)^{Footnote 16,Footnote 17}, the United Kingdom (n=3)^{Footnote 18,Footnote 19}, the United States (n=1)^{Footnote 20}, Spain (n=2)^{Footnote 21}, Viet Nam (n=1; clade not confirmed at time of writing)^{Footnote 17,Footnote 22}, Ecuador (n=1)^{Footnote 16} and Chile (n=1)^{Footnote 23}. Human-to-human transmission has not been reported. Clinical severity has varied widely; the avian influenza A (H5N1) cases reported in humans from Europe and North America were asymptomatic or mild, while those in Asia and South America were severe or fatal. Almost all cases had known exposure to infected poultry. Exposure information was limited for the Chilean case, although highly pathogenic avian influenza A(H5) was detected in wild birds and sea lions in the area in which the case resided. ^{Footnote 24} This case was notable because the virus identified from the Chilean patient had two mutations in the polymerase basic protein 2 (PB2) that have been shown to contribute to mammalian adaptation in experimental animal models. ^{Footnote 25} In May 2023, avian influenza A(H5N1) clade 2.3.4.4b virus was detected in nasal swab specimens from two asymptomatic poultry farm workers in the UK as part of a voluntary testing program for individuals exposed to infected birds.^{Footnote 19} Virus detection in one of these two individuals is thought to have resulted from contamination of the nasal passages through inhalation of virus, rather than true infection.^{Footnote 19}

It is possible that human infections are under-detected, due to reliance on passive surveillance and limited testing of individuals exposed to infected animals. Mild and subclinical cases are likely to be detected only as part of special investigations during animal outbreaks or contact tracing for a confirmed human case.

In June 2022, the Public Health Agency of Canada (PHAC) analyzed the risk to humans from avian influenza A(H5N1) in Canada. At that time, the risk of infection with avian influenza A(H5N1) for the general population with limited contact with infected animals was considered to be low. The assessment is being updated due to continued widespread circulation of avian influenza A(H5N1) clade 2.3.4.4b in wild and domestic bird populations, the increasing range of mammalian species in which infection with this virus has been reported, and additional reports of isolated human cases in other countries.

Methods

This assessment was led by CDSB-CIRA, within the Public Health Agency of Canada (PHAC) in May and June 2023, and conducted in collaboration with a multi-sectoral team. The rapid risk assessment (RRA) methodology used by CDSB-CIRA has been adapted from the Joint Risk Assessment Operational Tool (JRA OT) to assess the risk posed by zoonotic disease hazards ^{Footnote 26}, developed jointly by the World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO), and the World Organization for Animal Health (WOAH). PHAC has adapted the JRA OT by modifying the likelihood and impact scales and associated definitions to incorporate elements from other RRA frameworks that are relevant to the Canadian context. ^{Footnote 27,Footnote 28}

Detailed methodology outlined in Appendix A.

Definitions

This risk assessment focuses on the risk of human infection with avian influenza A(H5N1) clade 2.3.4.4b virus in Canada from zoonotic or environmental exposures (due to animal contamination). Exposure risks related to contact with a human case are not included. If human-to-human transmission were to occur with this virus, a separate risk assessment would be conducted that includes such exposure risks, e.g., those experienced by close contacts of cases and healthcare workers.

Refer to Appendix B for a list of occupational and recreational groups with potentially relevant exposures.

Key assumptions

• Relatively little is known about the epidemiological or viral characteristics of avian influenza A(H5N1) clade 2.3.4.4b viruses and this assessment assumes some similarities with other highly pathogenic avian influenza (HPAI) viruses.
• This assessment assumes that there will be no significant genetic changes to the currently circulating avian influenza A(H5N1) clade 2.3.4.4b viruses during the assessment period that would influence infectivity, transmissibility, or clinical severity in humans.
  • This assessment considers all avian influenza A(H5N1) viruses belonging to clade 2.3.4.4b currently in circulation at the time of this assessment.
• Pathway assumptions:
  • Infection routes for humans are primarily through respiratory and/or mucous membrane contact irrespective of animal source and/or human exposure groups (occupational/recreational), but it is assumed that, where applicable, prevention and control guidance will recommend measures to avoid all possible infection routes, which may include handling and consumption of raw or undercooked, contaminated animal products.
  • There is limited information regarding the susceptibility to and prevalence of infection in many of the different bird and animal species. To provide more precautionary estimates of the likelihood of infection (i.e., representing the worst-case scenario), the following guidance was used for estimating the likelihood of infection in different animal groups:
    • Wild birds: birds known to be susceptible to infection based on current evidence (e.g., Anseriformes and Charadriiformes).
    • Domestic mammals: mammals known to be susceptible to infection to some degree based on current evidence (e.g., cats and dogs); note that farmed mammals were not expressly included in this assessment as part of domestic mammals, although farmed mink are known to be susceptible, and a recent study found serological evidence of infection in swine.^{Footnote 11,Footnote 12}
    • Wild mammals: mammals known to be susceptible to infection based on the current evidence (e.g., terrestrial and marine mammals).

Detailed risk assessment results

Risk pathway

Risk pathway depicting sources and exposures leading to, and impacts of, a human infection with avian influenza A(H5N1) clade 2.3.4.4b in Canada by the end of the 2023 fall bird migratory season (generally ranging from October to December in Canada). Refer to Appendix A for explanation of the use of the risk pathway to develop risk sub-questions.

Figure 1: Text description

The likelihood of such an infection is dependent on the prevalence of infection in different groups of animals (Questions 1a-1e), combined with the likelihood of exposure to a sufficient amount of virus to potentially cause infection following different types of animal contact (Questions 2a-2b), and then combined with the likelihood that an individual exposed to a sufficient amount of virus actually develops infection (Question 3). The impact estimates presented in Table 4 include consideration of the most likely spread scenario were a human case to occur in Canada (Question 4), together with the magnitude of effects on infected individuals (Question 5) and the overall impact for the Canadian population (Question 6).

Likelihood and impact estimates

Estimates of the likelihood of a human infection with avian influenza A(H5N1) clade 2.3.4.4b in Canada resulting from exposure to infected birds or mammals by the end of the 2023 fall bird migratory season are presented in Table 3, together with associated rationales and uncertainty estimates. The likelihood of such an infection is dependent on the prevalence of infection in different groups of animals (Questions 1a-1e), combined with the likelihood of exposure to a sufficient amount of virus to potentially cause infection following different types of animal contact (Questions 2a-2b), and then combined with the likelihood that an individual exposed to a sufficient amount of virus actually develops infection (Question 3). The likelihood scale used in this assessment is described in Table A2.

The impact estimates presented in Table 4 include consideration of the most likely spread scenario were a human case to occur in Canada (Question 4), together with the magnitude of effects on infected individuals (Question 5) and the overall impact for the Canadian population (Question 6). The magnitude of effects and impact scales used in this assessment are described in Table A3 and Table A4.

Risk estimate summary

Based on the available data at this point in time, up to the end of the 2023 fall bird migratory season (generally ranging from October to December in Canada):

• The overall risk to the general population from lower or negligible exposure to either birds or mammals (number 2 in Figure 2 in darker green area) is low.
• The risk for those with higher exposure to either birds or wild mammals is "increased" compared to the risk experienced by the general population (number 1 in Figure 2 in the lighter green-yellow area)

Figure 2: Text description

Risk matrix depicting the overall level of risk for the general population (indicated with the number 2) and populations with higher exposure to bird and/or mammals (indicated with the number 1). A scale of likelihood is along the vertical axis with very unlikely at the bottom to highly likely at the top. A scale of impact is along the horizontal axis with minimal to the far left and severe on the far right. The risk matrix is a gradient with the lowest overall risk in the bottom left corner (darkest green) and highest overall risk in the top right corner (bright red).

Limitations

This assessment does not explicitly consider the frequency of human interactions with different types of animals; the size of different animal populations; or geographic variations in the distribution of animal populations, infection prevalence in animal species and human-animal contacts.

The qualitative method used for the likelihood estimation leads to an over-inflation of likelihood since the cumulative effect of probabilities less than 100% along the pathway will reduce the likelihood in a way that cannot be captured without quantitative data. This bias is in line with the use of the precautionary principle.

There was substantial variation in initial estimates provided by multi-sectoral experts to pathway sub-questions related to the likelihood of infection in different animal groups. Analysis of rationales provided by experts for their estimates indicated that the question had been interpreted in two different ways by Technical Team members, resulting in a divergence of estimates. The intended interpretation of the questions was subsequently clarified and revised likelihood estimates derived after discussion with Technical Team members and review of relevant evidence.

The wording of questions 2a and 2b (and associated naming of exposure levels) were changed during the review process to improve clarity. In the poll the questions were worded as follows: "What is the likelihood of at least one person getting exposed to sufficient amount of virus to potentially cause an infection for the average person following a higher/lower dose contact".

Knowledge gaps

The key scientific uncertainties and knowledge gaps in this assessment are included below (refer to Table 5).

Acknowledgements

Completed by the Public Health Agency of Canada's Centre for Integrated Risk Assessment within the Corporate Data and Surveillance Branch.

The individuals listed, along with their affiliated agencies, are acknowledged for their contributions to this report.

Alberta Health/Alberta Agriculture and Irrigation: Hussein Keshwani

British Columbia Centre for Disease Control: Erin Fraser, Linda Hoang, Agatha Jassem, Samantha Kaweski, Shannon Russell, Inna Sekirov, Danuta Skowronski

British Columbia Ministry of Agriculture: Theresa Burns, Chelsea G. Himsworth

Cadham Provincial Laboratory (Manitoba): Paul Van Caeseele

Canadian Food Inspection Agency: Tamiru Alkie, Yohannes Berhane, Maud Carron, Caroline Dubé, Andrea Ellis, Logan Flockhart, Kathleen Hooper, Charles Nfon, Marc Sabourin, Primal Silva

Canadian Veterinary Medical Association: Mike Petrik

Canadian Wildlife Health Cooperative: Damien Joly

Environment and Climate Change Canada: Michael Brown, Brigitte Collins, Jolene Giacinti, Jack Hughes, Daniel Leclair, Hannah Lewis

Fisheries and Oceans Canada: Ole Nielsen

Indigenous Services Canada: Shawn Donaldson, Amole Khadilkar, Maxime Trubnikov

Institut national de santé publique du Québec: Cassi Bergeron-Caron, Maude Bigras, Hugues Charest, Judith Fafard, Alejandra Irace-Cima

Manitoba Agriculture: Dale Douma

Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec: Isabelle Picard

Ministère de la santé et des services sociaux du Québec: Josée Dubuque, Colette Gaulin, Juliette Martin

New Brunswick Public Health Laboratories: Richard Garceau

Nova Scotia Health Authority: Todd Hatchette, Jason Leblanc

Ontario Ministry of Agriculture, Food and Rural Affairs: Maureen Anderson, Paul Innes

Ontario Ministry of Health: Melissa Helferty

Parks Canada: Todd Shury

Prince Edward Island Chief Public Health Office: Karen Phillips

Public Health Agency of Canada: Rukshanda Ahmad, Sandra Radons Arneson, Nicole Atchessi, Dima Ayache, Christina Bancej, Nathalie Bastien, Philippe Belanger, Anna Bellos, Samuel Bonti-Ankomah, Natalie Bruce, Peter Buck, Sharon Calvin, Taeyo Chestley, Mette Cornelisse, Lesley Doering, Catherine Elliott, Raquel Farias, Aamir Fazil, Manon Fleury, Vanessa Gabriele-Rivet, Eleni Galanis, Corey Green, Heather Hannah, Marianne Heisz, Kirsten Jacobsen, Emmanuelle Jean, Nina Jetha, Danielle Julien, Mira Kelada-Antoun, Darwyn Kobasa, Lisa Landry, Erin Leonard, Tiffany Locke, Aaron MacCosham, Janice Merhej, Rachel Milwid, Rhonda Mogk, Nicholas Ogden, Toju Ogunremi, Nicole Pachal, Renee Parisien, Matthew Peake, Kirsten Querbach, Charlene Ranadheera, Simran Sandhu, Jill Sciberras, Lisa Slywchuk, Ming Su, Clarence Tam, Joe Tanelli, Francois-William Tremblay, Jan Trumble-Waddell, Linda Vrbova, Lisa Waddell, Lindsay Whitmore

Public Health New Brunswick: Jackie Badcock, Renee Bourque, Carole Breau, Shelley Landsburg, Arifur Rahman

Public Health Ontario: Maan Hasso, Emily Karas, Richard Mather, Karam Ramotar

Sunnybrook Health Sciences Centre: Samira Mubareka

Appendix A: Methods

The Centre for Integrated Risk Assessment at PHAC convened a Canadian One Health multi-sectoral team that formed two committees: the Rapid Risk Assessment (RRA) Steering Committee and the RRA Technical Team. The Steering Committee (largely comprised of senior managers and decision makers) defined the hazard, agreed on the purpose and key objectives for the assessment, outlined the scope, drafted the risk question, and reviewed the recommendations. The Technical Team (largely comprised of those with expertise and/or information related to the assessment) characterized the risk by providing qualitative estimates of likelihood, impact and uncertainty in relation to the risk questions being assessed, based on the available evidence and expert opinion. The Canadian One Health multi-sectoral team consisted of federal, provincial and academic experts from human, animal, and ecosystem health sectors, representing a variety of disciplines such as epidemiologists, virologists, wildlife biologists, veterinarians, and physicians.

The risk question being assessed was visualized using a risk pathway (Figure 1), a diagrammatic representation of the key components of the sequence of the hazard from its source to its infection of the host of interest. Each step in the risk pathway is associated with a likelihood or impact sub-question that was then addressed as part of the risk assessment. The risk pathway and sub-questions also included the animal and exposure sub-groups listed in Table 2.

The Technical Team were introduced to the risk pathway and associated questions in a meeting. Subsequently, a poll was used to obtain initial, independently assessed qualitative estimates from Technical Team members on the likelihood or impact associated with each risk pathway sub-question, using standardized qualitative scales (Tables A1-A4 below). The risk pathway, a slide deck explaining exposure groups, definitions for likelihood and impact and an evidence table were provided to assist each expert in making their best-considered estimation of risk. For each estimate, members were also asked to provide a rationale, indicate the level of uncertainty associated with their estimate and give a short explanation of the factors influencing this uncertainty. Lastly, members were given the option to not answer specific questions if they lacked sufficient expertise.

The poll results were used as a basis for discussion; final estimates were based on discussion with the Technical Team and review of the draft report by Technical Team and Steering Committee. A summary of poll responses was presented to Technical Team members in a meeting following the poll, highlighting where estimates and rationales clearly converged, and areas where poll results suggested differing interpretations of the questions or divergent estimates or rationales. Estimates and rationales that aligned with a common understanding of the rapid risk assessment questions were finalized based on subsequent discussions, as well as feedback through draft document review by the Technical Team and final review and feedback by the Steering Committee. In addition, Technical Team members were asked to identify key uncertainties and knowledge gaps that influenced their level of uncertainty in likelihood and impact estimates during the poll and in meetings. These were consolidated into a list of key uncertainties and knowledge gaps related to this risk assessment (Table 5).

Definitions of likelihood (Table A2), impact (Table A3 and Table A4), and uncertainty (Table A1) are provided below. Since the risk pathway describes the sequence of events leading up to the undesired outcome, the likelihood of each event is conditional on the likelihood of preceding steps in the risk pathway, as assessed in the estimation process for each risk pathway sub-question. The likelihood for the overall risk question is therefore determined by the lowest likelihood estimated along the risk pathway. A risk matrix, adapted from WHO (2012), is used to integrate the likelihood and impact estimates into a summary risk estimate to support risk communication. Summary risk estimates are presented in context with the likelihood and impact estimates, given the known limitations of risk matrices.^{Footnote 47}

The findings and conclusions represent the consensual, but not necessarily unanimous, opinions of experts contributing to this risk assessment, and should not be interpreted as representing the views of all participants and their respective organizations. Evidence was gathered by scientific experts using a rapid, non-systematic literature search and includes published articles and pre-print manuscripts, reports on the current outbreak including surveillance reports, and communication from multi-sectoral experts. Where appropriate, some references have been included; where references are not included this evidence was informed by input from the subject matter experts.

Appendix B: Occupational and recreational groups with potentially relevant exposures

The population with either occupational or recreational exposure to potentially infected wild birds, poultry, or mammals, their carcasses or highly contaminated environments includes the following:

• Poultry farm worker
• Backyard/small poultry flock owner
• Poultry processing plant worker
• Poultry culler (catching, bagging, transporting, or disposing of dead birds)
• Dealer, breeder, or handler of pet and other birds (e.g., exotics, falconry, racing pigeons)
• Butcher or person working with live or recently killed poultry or other potentially affected animals
• Person working in live animal market
• Veterinarian or other animal health worker
• Wildlife officer or biologist collecting specimens or euthanizing birds or mammals
• Wildlife rehabilitator
• Person performing permitted activities with wildlife (e.g., bird banding, capturing, sampling, removal, restoration, etc.)
• Person involved in hunting and trapping including Indigenous harvester
• Laboratory worker or researcher working with wild birds and/or mammals
• Caretaker of animals (e.g., pets, guardian dogs, hunting dogs) that regularly interact with wild birds or other potentially affected stray, or wild animals
• Person with other significant occupational or recreational exposure to wild birds and other potentially affected animals (e.g., mink farmer, biologist)

Note: If human-to-human transmission starts occurring for this virus, then healthcare workers and other contacts of cases would also need to be included.