Assessing public health threats: An overview of coordinated threat assessment at PHAC

Abstract

Background: The early detection, assessment, and communication of potential public health threats are key activities in mitigating public health impacts by ensuring the timely deployment of an appropriate response. The Public Health Agency of Canada (PHAC) uses a standardized methodology to consolidate scientific and technical subject matter expertise on a weekly basis to systematically characterize and assess emerging public health signals and communicate assessments to decision-makers.

Methods: Public Health Agency of Canada’s coordinated threat assessment process, and the standardized methodology used to characterize and assess threats, are described.

Results: The coordinated threat assessment methodology uses a standardized method that includes engagement with subject matter experts across PHAC to assess, document, and communicate the characterization of each threat. Three key attributes are used to assess each threat based on the concern for human health, the potential to affect Canada, and the concern that Canada has insufficient control measures to manage a specific threat. Qualitative criteria for each threat attribute are used to assess a threat based on ‘high’, ‘moderate’, or ‘low’ levels. An overall assessment is based on the three threat attributes and is accompanied by a narrative rationale to support the assigned threat level.

Conclusion: The standardized threat assessment methodology provides a coordinated and systematic process to characterize and assess public health threats in a consistent and timely manner. The framework reflects important elements to consider in terms of public health significance, allows for flexibility in the indicators used to characterize a public health threat, and is applicable to any threat of public health concern.

Introduction

Public health intelligence is a core public health function responsible for detecting, assessing, interpreting, and communicating information for informed decision-making to protect the health of the population ^{Footnote 1}. These activities are key in mitigating public health impacts by ensuring the timely deployment of an appropriate response, and are in place in subnational, national, and international public health agencies ^{Footnote 2Footnote 3Footnote 4}. Some agencies follow a centralized approach, wherein a core team is responsible for all steps, including signal detection, assessment, and communication ^{Footnote 2Footnote 4}. Others follow a disseminated approach, with responsibility for these activities distributed among a variety of teams across the agency ^{Footnote 5}.

As part of the spectrum of public health intelligence activities, threat assessment is a high-level, early characterization of the public health significance associated with a specific signal or event ^{Footnote 4} using data and intelligence from multiple sources, as well as expert opinion ^{Footnote 6}. Indicators of public health significance are measured in different ways by different public health agencies, however, factors such as population health impact, potential for exposure or transmission, and the availability of public health control measures are often considered ^{Footnote 2Footnote 3Footnote 4}. The threat assessment process can be challenging due to limited or emerging data, however, a standardized methodology ensures all public health threats are characterized using a consistent approach to inform a public health response that is proportionate to the threat level ^{Footnote 6}.

At the Public Health Agency of Canada (PHAC), threat assessment is standardized through the coordinated threat assessment (CTA) process, which was established in response to recommendations identified by the Auditor General of Canada in 2021 to strengthen its risk assessment process and coordination to guide public health response ^{Footnote 7}. Situated within a spectrum of risk assessment activities, CTA is a PHAC-wide approach that consolidates data, information, and subject matter expertise on a weekly basis to systematically assess emerging public health signals that may constitute a threat to Canada and potentially require further public health action. Through the CTA process, a weekly threat report is produced and shared with public health partners to document and communicate an early, high-level assessment of emerging public health threats. This article provides an overview of PHAC’s CTA process and a description of the methodology used to assess threats. Table 1 contains a list of terms associated with threat assessment and their definitions.

Methods

Coordinated threat assessment methods

Overall process

The threat assessment process begins when PHAC detects a signal indicating a potential hazard to human health occurring either in Canada or internationally (Figure 1). Signals of potential public health threats may be related to a new hazard or a change in the epidemiology of an existing hazard. This includes, but is not limited to, an increase in morbidity or mortality in animals or humans, a change in the geographical or temporal distribution of a given hazard, an unexpected cluster of cases or deaths, the emergence or re-emergence of a pathogen, and hazards that have the potential to cause substantial morbidity or mortality in humans.

Figure 1 - Text description

This figure shows an overview of the weekly threat submission and assessment process conducted by the Public Health Agency of Canada (PHAC). Signal detection and validation is conducted by subject matter experts on an ongoing basis throughout the weekly cycle. A description and preliminary assessment for signals meeting standard submission criteria are drafted and submitted by Tuesday of each week. A weekly meeting of the Scientific Committee for Coordinated Threat Assessment occurs each Wednesday to discuss and determine the final assessment for each signal. The Weekly Threat Report is generated and communicated to PHAC senior leadership each Thursday. Additional risk assessments are considered for complex threats or those identified to require a more in-depth assessment of risk.

Signal detection and validation: Signals are detected through a variety of sources, including notification from subnational, national, and international partners, as well as event-based surveillance or indicator-based surveillance systems ^{Footnote 6Footnote 12}. Subject matter experts (SMEs) within PHAC validate signals to determine whether they have the potential to constitute a threat to Canada. The threat assessment process is initiated for signals that meet the specific submission criteria described in the threat assessment framework, described below.

Assessment: A preliminary threat assessment is provided by the submitting SME in collaboration with the CTA team using the standardized methodology. The final threat assessment is determined at a weekly meeting of the Scientific Committee for Coordinated Threat Assessment (SCCTA), which consists of scientific and technical public health experts with a wide breadth of expertise across PHAC. The consolidation of expert opinion using a standardized assessment tool results in a transparent and systematic measure of the public health threat level. Additional risk assessments are considered for complex threats or those identified by SMEs to require a more in-depth assessment of risk ^{Footnote 13}. Threats are reassessed on a weekly basis as a situation evolves, and more information becomes available.

Communication and documentation: Timely and clear communication of the threat level to PHAC senior leadership leads to a well-informed and common understanding of the threat to support decision-making for further action. The weekly threat report documents the signal, the assessment and rationale, as well as the public health actions undertaken by PHAC to address the threat.

A central team coordinates the process and is composed of epidemiologists and a medical director. Lead and supporting PHAC programs associated with each threat select a representative to contribute to the written submission and oral presentation at SCCTA. Subject matter experts in a variety of areas, including risk assessment, convene at SCCTA meetings to discuss and finalize the threat assessment for each submission.

Results

Threat assessment framework

Threat assessment at PHAC utilizes a standard framework that involves assessment of three threat attributes that characterize the public health significance of the event, and an overall threat level associated with the event (Figure 2) ^{Footnote 14}. The framework can be used to characterize threats affecting the general population or a specific subgroup, which may include populations at increased risk of severe harm due to biology (e.g., immune compromise, age), socioeconomic factors (e.g., access to care), or geography. Uncertainty in the data used to characterize a threat may elevate the assessment level of any of the attributes or the overall assessment.

Figure 2 - Text description

This figure represents a standardized threat assessment framework that includes submission criteria as well as a framework used to characterise and assess public health threats. The underlying principle of the submission criteria is that all threats submitted will be expected to have impact on Canada. The assessment framework involves the qualitative description of a public health threat using available data as well as expert opinion. It is meant to be a preliminary assessment associated with a specific signal and it consists of three threat attributes that can be assessed as high, moderate, or low using standard definitions. The framework includes an overall assessment level that is based on the assessment levels of the individual attributes.

Threat attributes

Each of the threat attributes is individually assessed and assigned a level of ‘high’, ‘moderate’, or ‘low’ based on the definitions in Table 2. These definitions allow for flexibility in the indicators used to characterize a threat and can be applied to any public health threat.

Concern for human health: Reflects the severity of harm posed to human health (Table 2). Indicators to consider for this attribute include morbidity, mortality, case fatality ratio, and burden of harm as it relates to physical, mental, or social well-being. When assessing concern for human health, the health consequences that are typically associated with the population most likely to be affected are considered. The level assigned for this attribute may vary depending on the context of the situation being assessed. For example, an outbreak of an enteric pathogen mainly involving populations at high risk of severe illness (e.g., children under the age of five years) may be assigned a higher level than the same pathogen affecting a group of young and middle-aged adults.

Potential to affect Canada: Describes the number of individuals or proportion of a population that will potentially be affected by a hazard (Table 2). Examples of indicators to consider include the transmissibility of a pathogen, the distribution of disease vectors in Canada, and the geographical range of a hazard, such as wildfire smoke. The number of people potentially or currently affected that would be considered high, moderate, or low will vary depending on the context of the event. For example, an assessment of ‘high’ may refer to a large proportion of a particular subgroup within Canada or a large number of people in the general population.

Concern for insufficient control measures: Relates to Canada’s capacity to engage in public health activities to detect or respond to a hazard (Table 2). Activities related to detection, prevention, mitigation, preparation, or response may be applicable at different stages of an event. For example, detection refers to whether Canada has sufficient surveillance and/or laboratory capacity to detect a hazard should it enter Canada and should be considered in the assessment of threats that have not yet entered Canada. In contrast, prevention and response refers to whether Canada has mechanisms, such as vaccines, therapeutics, safety protocols, and guidelines to prevent the spread of the hazard. In addition, some control measures are dependent on knowledge of the source of the hazard prior to implementation. For example, concern for insufficient control measures may be assessed at a higher level for a foodborne outbreak with no known source, because deployment of a food recall, an effective control measure, is dependent on knowledge of the source of the outbreak.

Overall threat assessment

The overall threat assessment provides a single assessment that communicates the threat level, allowing decision-makers to better understand the degree to which public health action is needed for a given threat. All three attributes are taken into account when determining the overall assessment, although they may not receive equal weight. As outlined in Table 3, a pathogen associated with severe or fatal outcomes may receive a low overall assessment if it is unlikely to affect Canada and can be effectively managed should it occur. Recognizing the subjectivity of this approach, the final overall assessment level is made by group consensus during SCCTA meetings.

Rationale for the overall threat assessment

A narrative rationale for the overall threat assessment level provides the context within which each threat is assessed and supports the assigned threat level based on the information used to make the assessment. The rationale describes the level of each individual threat attribute, and the way it contributes to the overall assessment of the threat. This includes any nuance in the reasoning behind the level selected for the individual threat attributes and overall threat assessment, key information gaps, and associated uncertainty related to the assessment.

Discussion

The coordinated threat assessment process at PHAC was created in response to recommendations from the Auditor General of Canada’s 2021 report on pandemic preparedness, surveillance, and border measures following the COVID-19 pandemic ^{Footnote 7}. The objective of PHAC’s coordinated threat assessment process is to produce a quick, timely snapshot of threats for PHAC senior leadership using standardized methodology. This process provides a systematic scientific approach to assess varied threats from across PHAC programs by consolidating emerging data and SME opinion on a weekly basis. The process established at PHAC optimizes the ability to anticipate, detect, understand, and respond to potential public health threats through communication of timely assessments and corresponding actions for public health partners within PHAC and across Canada.

While different public health agencies vary in their processes and hazard priorities, many agencies employ a standard tool to characterize and assess public health threats ^{Footnote 2Footnote 3Footnote 4Footnote 5}. Public Health Agency of Canada’s standardized threat assessment tool reflects three key elements to consider in terms of public health significance, ensuring a consistent methodology is applied to a wide variety of threats with transparent outcomes.

Limitations

A critical principle of the threat assessment framework is that the application of the threat attributes is qualitative and flexible and can be applied to any public health threat of concern to Canada. Flexibility in the application of the framework is key, given the breadth of data and intelligence that may be used to inform the assessment. For example, an event associated with a pathogen will use different indicators to assign a level to individual threat attributes compared to an event associated with a natural disaster. The former may characterize concern for human health using the case fatality ratio, whereas the latter may rely on burden of harm to mental health. The rationale for the threat assessment provides context for the selected level and ensures transparency in the assessment regardless of the indicators used to arrive at the assessment level.

The qualitative nature of the threat assessment definitions can make it challenging to assign a level of ‘high’, ‘moderate’, or ‘low’ for each section without quantitative guidelines. However, this subjectivity allows for expert opinion influencing the assessment of threats and flexibility in weighting threat attributes based on the context of the event. The approach also allows for discordant opinions, which are discussed during SCCTA meetings and resolved by group consensus.

Some public health agencies take an all-hazards approach ^{Footnote 2}, while others are focused on infectious diseases ^{Footnote 3Footnote 4}. At the time of writing, the majority of threats assessed by PHAC have been related to infectious diseases, however, a small number of non-infectious disease threats have been submitted to the threat report (e.g., environmental hazards, mis/disinformation). While such signals are often the responsibility of other government departments, there is ongoing work to expand the scope of the CTA process to include a broader spectrum of health hazards ^{Footnote 15Footnote 16}. Recognizing the increasingly interconnected and complex nature of natural and human-induced hazards and their potential impact on health ^{Footnote 16}, an approach that includes infectious and non-infectious hazards increases efficiency by recognizing and integrating common threat assessment elements across hazard types. Accordingly, the threat assessment framework described in this paper was designed with an inclusive approach in mind and is expected to remain applicable in assessing threats associated with diverse hazard types.

Conclusion

In summary, public health intelligence, including threat assessment, is a key component of public health infrastructure. Early assessment of threats can be challenging with limited and emerging information, however, a standardized methodology ensures all public health threats are characterized using a consistent approach. The implementation of CTA across PHAC has improved the process and transparency of risk assessment activities and fosters relationships by sharing results with public health partners.

Authors' statement

GB — Conceptualization, project administration, writing–original draft, writing–review & editing
EB — Writing–original draft, writing–review & editing
RA — Conceptualization, writing–review & editing, supervision
CD — Project administration, writing–review & editing
CE — Conceptualization, writing–review & editing
EG — Conceptualization, writing–review & editing, supervision
JM — Project administration, writing–review & editing
AS — Project administration, writing–review & editing
LW — Conceptualization, writing–review & editing, supervision

Competing interests

None.

ORCID numbers

None.

Acknowledgements

None.

Funding

This work was supported by the Public Health Agency of Canada.

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