Canadian respiratory virus surveillance report: Influenza

Weekly overview of key trends in influenza (flu) activity in Canada.

  • Last updated: 2024-11-01

Update schedule: Data in this report are updated every Friday. This page was last updated on September 27th, 2024, 10am ET, with data up to and including ... (surveillance week ...).

Highlights  for the week ending (week )

Influenza and influenza-like illness activity: Geographic spread

Figure 1: Map of influenza/ILI activity by reporting region in Canada, week (week ending )

Hover over the map below to learn more about the current influenza and ILI activity levels in each of Canada's health regions. To get a closer look at the regions, scroll while hovering over the map to zoom in or out. Click on a specific region to highlight and focus on it, and click on it again to zoom out to the default view.

Figure 1: Text description
Figure 1 and influenza activity levels: Data notes

Geographic spread of influenza and influenza-like illness

All provincial and territorial public health departments provide an assessment of the intensity and geographic spread of influenza for surveillance regions within their jurisdictions. For each surveillance region, the number of reported influenza detections, health care visits due to ILI and influenza outbreaks are assessed and assigned a level of activity (no activity, sporadic, localized, and widespread).

  • Not all provinces and territories provide activity levels data for influenza.
    • 12/13 PTs, representing approximately 97% of the population in Canada, provide activity level data for influenza.
    • Note: the number of participating PTs may fluctuate over the course of the season.
  • Activity level definitions may not be uniformly applied across all regions/PTs but serve as a rough operational definition to enable comparability of levels across jurisdictions in Canada.

Indicators

  1. Geographic spread of influenza (Regional)

Definitions

No activity
No laboratory-confirmed influenza detections in the reporting week; however, sporadically occurring ILI may be reported.
Sporadic
Sporadically occurring ILI and laboratory-confirmed influenza detection(s) with no outbreaks detected within the influenza surveillance region.
Localized
Evidence of increased ILI and laboratory-confirmed influenza detection(s) and outbreaks in facilities under surveillance occurring in less than 50% of the influenza surveillance region.
Widespread
Evidence of increased ILI and laboratory-confirmed influenza detection(s) and outbreaks in facilities under surveillance occurring in greater than or equal to 50% of the influenza surveillance region.

Laboratory-confirmed detections

Figure 2: Number of reported influenza detections and percentage of tests positive in Canada, by type, subtype, and report week

Figure 2: Text description

Figure 3: Percentage of tests positive for influenza in Canada for season 2024-2025 compared to previous seasons

Figure 3: Text description
Figure 3: Data notes

The epidemic threshold is 5% tests positive for influenza. When it is exceeded, and a minimum of 15 weekly influenza detections are reported, a seasonal influenza epidemic is declared.

Figure 4: Number of detections in Canada, by age group and report week

Figure 4: Text description

Figure 5: Proportion of influenza detections in Canada for season 2024-2025 by and by age group

Figure 5: Text description
Influenza laboratory-confirmed section: Data notes

Laboratory-confirmed influenza detections

  • Data are collected through the Respiratory Virus Detection Surveillance System (RVDSS). RVDSS is a long-standing laboratory surveillance system consisting of provincial, territorial, and regional public health laboratories and some hospital laboratories. There are reporting laboratories in all provinces and territories, but not all respiratory virus testing in Canada is captured through RVDSS. Laboratories report data for up to 8 respiratory viruses:
    • SARS-CoV-2 (the virus that causes COVID-19)
    • Influenza (commonly referred to as the flu)
    • Respiratory syncytial virus (RSV)
    • Human parainfluenza virus
    • Adenovirus
    • Human metapneumovirus
    • Enterovirus/rhinovirus
    • Human coronavirus 229E/OC43/NL63/HKU1 (does not include SARS-CoV-2)
  • Laboratories perform molecular testing for these viruses and report the number of tests and positive detections for each virus each week throughout the year.
  • Most tests are conducted on:
    • acute respiratory infection cases at emergency departments
    • hospitalized severe acute respiratory virus infection cases
    • outbreak cases
  • Respiratory virus trend assessments (increasing/decreasing/stable) are currently based on PHAC subject matter expert interpretation of week-to-week changes in respiratory virus laboratory detections and percent positivity. Set thresholds for trend assessment are under development.
  • Unless otherwise specified, the term influenza includes influenza A and influenza B positive detections.
  • Some public health laboratories in Canada perform subtyping on influenza specimens from other laboratories. When identified, these subtype detections are not included in total influenza A detection counts; in these instances, total influenza A detection counts may not equal the sum of influenza A subtype detections. Total influenza A and B positive counts are used to calculate percentage of tests positive.
  • Testing for influenza and other respiratory viruses has been influenced by the COVID-19 pandemic. Changes in laboratory testing practices may affect the comparability of data to previous seasons.

Laboratory indicators

  1. Number of tests positive by week for influenza (National)
  2. Number of tests performed by week for influenza (National)
  3. Percentage of laboratory tests positive by week for influenza (National)

Case-level laboratory-confirmed influenza detections

  • Participating provincial and territorial public health laboratories provide the age and sex of influenza detections to monitor the impact of the viruses in different age-groups.
  • Not all provinces and territories provide case-level laboratory data for influenza.
    • 12/13 PTs, representing approximately 99% of the population in Canada, provide case-level laboratory data for influenza.
    • Sentinel hospital sites do not provide case-level laboratory data for influenza.
  • Case-level data represents a portion of laboratory-confirmed detections for influenza.

Case-level laboratory indicators

  1. Number of laboratory-confirmed detections of influenza by type/subtype and age-group (National)
  2. Proportion of laboratory-confirmed detections of influenza by type/subtype and age-group (National)

Influenza strain characterization

Antigenic characterization

Changes in circulating influenza viruses are monitored by antigenic characterization. Antigenic characterization results show how similar the circulating viruses are to reference viruses. Reference viruses represent strains included in the current seasonal influenza vaccine.

Influenza A(H1N1)

Influenza A(H3N2)

Influenza B

Genetic characterization

Genetic characterization is used to determine how similar gene sequences of circulating influenza viruses are to the sequences of the vaccine components used in the current seasonal influenza vaccine.

Table 1: Genetic characterization results of influenza A(H1N1), influenza A(H3N2), and influenza B in Canada, 2024-2025 season

Antiviral resistance

The National Microbiology Laboratory Branch (NMLB) also assesses the antiviral resistance of influenza viruses received from Canadian laboratories.

Table 2: Antiviral resistance results of influenza A(H1N1), influenza A(H3N2), and influenza B in Canada, 2024-2025 season
Influenza strain characterization and antiviral resistance: Data notes

The National Microbiology Laboratory Branch (NMLB) receives influenza isolates from participating provinces and territories throughout the year. The NMLB provides the FluWatch+ program with the strain characterization and antiviral resistance testing on a weekly basis.

Specimens tested by the NMLB represents a portion of laboratory-confirmed influenza detections. Provincial and Territorial public health laboratories are encouraged to submit a representative proportion (up to 10%) of positive specimens to the NMLB.

Not all provinces and territories submit specimens to the NMLB for characterization and antiviral testing.

Syndromic

See what is happening in your neighbourhood! Downloadable datasets are also available on Open Maps. The FluWatchers program is always looking for more volunteers: Sign up to be a FluWatcher.

Figure 6: Percentage of FluWatchers reporting cough and fever in Canada, season 2024-2025, compared to previous seasons

Figure 6: Text description

Figure 7: Percentage of tests positive for COVID-19, influenza, and RSV compared to the percentage of FluWatchers reporting cough and fever in Canada, 2023-2024 season

Figure 7: Text description

Outbreaks

Figure 8: Number of laboratory-confirmed outbreaks in Canada associated with influenza, by setting and report week, 2024-2025 season

Figure 8: Text description

Figure 9: Cumulative proportion of laboratory-confirmed outbreaks associated with influenza in Canada by in the 2024-2025 season

Figure 9: Text description
Influenza outbreaks section: Data notes

Outbreaks of laboratory-confirmed influenza in high-risk settings (long-term care facilities, acute care facilities, retirement facilities, remote and/or isolated communities and other settings) are reported from provincial and territorial public health departments. The distribution of outbreaks by setting provides a timely, sensitive measure of early influenza activity that is scalable from a local to national level. It provides evidence of the burden of influenza within various closed settings and at-risk populations.

  • Not all provinces and territories provide outbreak data.
    • 13/13 provinces and territories provide outbreaks data for influenza.
  • Note: the number of participating provinces and territories may fluctuate over the course of the season.
  • Outbreak definitions and facility types may not be uniformly applied across all regions/provinces and territories but serve as a rough operational definition across jurisdictions in Canada.
  • Not all provinces and territories conduct surveillance in all facility types.
  • Not all jurisdictions within a provinces or territory report outbreaks.
  • Due to data collection practices in some provinces and territories, some outbreaks cannot be confirmed to be due to a specific virus; thus, the terms “associated with” or “detected” are used when reporting outbreaks nationally.

Indicator

  1. Number of laboratory-confirmed influenza outbreaks

Definitions

Setting Setting definition Outbreak definition
Long-term care facilities Facilities that provide living accommodation for people who require on-site delivery of 24 hour, 7 days a week supervised care, including professional health services, personal care and services such as meals, laundry and housekeeping or other residential care facilities. Provincial/territorial public health is responsible for outbreak management under provincial legislation for these facilities. 2 or more cases of ILI within 7 days, and at least 1 laboratory-confirmed case of influenza in the same setting (on the same floor, or in the same unity or ward).
Acute care facilities Publicly funded facilities providing medical and/or surgical treatment and acute nursing care for sick or injured people, through inpatient services. (i.e. hospitals including inpatient rehabilitation and mental facilities). Unusual or unexpected number of ILI cases within 7 days and at least 1 laboratory-confirmed case of influenza.
Retirement facilities A residential complex, or part of a residential complex that is: occupied primarily by persons who are 65 years of age or older, occupied by at least six persons not related to the operator, AND where the operator makes at least two care services available to residents. The residential complex provides accommodation, meals, housekeeping, linen and recreational services for residents that are able to move independently or with the assistance of one other person. Residents are medically and physically stable, who may be living with physical disability, mental health diagnoses, or mild dementia. Example facilities:
  • retirement homes
  • retirement residences
  • senior living facilities
  • designated supported living facilities (occupied primarily by persons who are 65 years of age or older)
 2 or more cases of ILI within 7 days, and at least 1 laboratory-confirmed case of influenza.
Note: Specific to setting as determined by reporting province
Remote and/or isolated communities A community that is physically and/or socially separated from the surrounding population. For example, communities that are geographically isolated due to limited transportation links. 2 or more cases of ILI within 7 days, and at least 1 laboratory-confirmed case of influenza in the same setting (on the same floor, or in the same unity or ward).
Other Any other locations/facilities not previously identified in which an outbreak of the influenza, RSV, COVID-19 or ILI occurs. Example facilities:
  • assisted living or hospice settings
  • private hospitals/clinics
  • correctional facilities
  • colleges/universities
  • schools/daycares
  • adult education centres
  • shelters
  • group homes
  • workplaces
  • supported living facilities/supportive housing/assisted living facilities for individuals with disabilities
  • group homes
  • residential treatment centres
 Unusual or unexpected number of ILI cases within 7 days and at least 1 laboratory-confirmed case of influenza.

Severe outcomes

Influenza severe outcomes surveillance

Influenza severe outcomes: Data notes

Provincial/territorial severe outcomes surveillance

Hospitalizations, ICU admissions, and deaths associated with influenza (influenza type/subtype), by age or age group, are reported from provincial and territorial public health departments.

  • Not all provinces and territories provide severe outcomes data.
    • 9/13 PTs, representing approximately 25% of the population in Canada, provide severe outcomes data for influenza.
    • Note: the number of participating PTs may fluctuate over the course of the season.
  • Hospital admissions and/or deaths don't have to be directly caused by influenza; a positive test is sufficient for reporting.

Indicators

  1. Cumulative rate (per 100,000 population) of influenza-associated hospitalizations by age-group, by week.
  2. Weekly rate of influenza-associated hospitalizations by age-group, by week.
  3. Cumulative number of influenza-associated hospitalizations, ICU admissions, and deaths.
  4. Cumulative rate (per 100,000 population) of influenza-associated ICU admissions, by week.

Definitions

Hospitalizations
Any person admitted to hospital with laboratory-confirmed influenza.
ICU admissions
Any person with laboratory-confirmed influenza admitted to an intensive care unit (ICU) or requiring mechanical ventilation.
Deaths
A death occurring in any person with laboratory-confirmed influenza with no period of complete recovery between illness and death.

Influenza vaccine monitoring

Vaccine monitoring refers to activities related to the monitoring of influenza vaccine coverage and vaccine effectiveness.

Vaccine coverage
Influenza vaccine coverage estimates for the 2024-2025 season are anticipated to be available in February or March 2025.
Vaccine effectiveness
Influenza vaccine effectiveness estimates for the 2024-2025 season are anticipated to be available in February or March 2025.

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