Overview of influenza monitoring in Canada

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FluWatch is Canada's national surveillance system that monitors the spread of influenza and influenza-like illnesses on an ongoing basis.

FluWatch reports, posted every Friday, contain information on flu activity in Canada.

The FluWatch program consists of a network of labs, hospitals, doctor's offices and provincial and territorial ministries of health. Program objectives are:

  • DETECT: Identify signals to detect, assess and respond to epidemics and other events of public health concern.
  • INFORM: Contribute to the evidence base necessary to plan, develop and implement health programs and policies for the control of influenza.
  • ENABLE: Support national infrastructure for influenza surveillance, including national and international collaborations related to surveillance and pandemic response.

FluWatch consists of seven surveillance systems components and together they provide a national picture of influenza activity in Canada.

Seven components of influenza surveillance in Canada

1. Geographic spread of influenza/influenza-like Illness activity

FluWatch monitors when and where influenza and influenza-like illness is occurring across Canada, and describes the groups of people that are being most affected through this surveillance component.

The level of influenza or influenza-like illness (ILI) activity for each region is determined by provincial and territorial ministries of health. The activity level assigned is based on laboratory confirmations of influenza, increases in health care visits for ILI and reported outbreaks of influenza or ILI. Influenza surveillance regions within the province or territory are defined by provincial and territorial ministries of health.

Influenza/ILI activity level definitions
No activity:
No laboratory tests positive for influenza in the reporting week, however, sporadically occurring ILI may be reported
Sporadic:
Sporadically occurring ILI and laboratory tests positive for influenza with no outbreaks detected within the influenza surveillance region
Localized:
Evidence of increased ILI; and laboratory tests positive for influenza; and outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance region
Widespread:
Evidence of increased ILI; and  laboratory tests positive for  influenza; and outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in greater than or equal to 50% of the influenza surveillance region

2. Laboratory-confirmed detections

FluWatch analyses the pattern of influenza circulation in Canada, to determine the beginning, peak and end of the season through this surveillance component.

Provincial, regional and some hospital laboratories report the weekly number of tests requested and the number of tests positive for influenza and other respiratory viruses. Specimens from the territories are sent to reference laboratories in the provinces for testing.

Provincial public health laboratories submit demographic information for cases of influenza in order to monitor the impact of circulating influenza strains in different age-groups. This case-level data represents a portion of laboratory-confirmed influenza detections.

Laboratory-confirmed influenza detection definition:

Isolation of influenza virus, demonstration of influenza virus antigen, or detection of influenza RNA, in an appropriate clinical specimen; or significant rise (e.g. fourfold or greater) in influenza IgG titre between acute and convalescent sera.

3. Syndromic surveillance

FluWatch analyses the pattern of influenza-like illness (ILI) circulation in Canada, to determine the beginning, peak and end of the season through this surveillance component. ILI, or syndromic surveillance is able to detect signals of increased influenza activity early, before formal diagnoses are confirmed and reported to public health agencies.

The Sentinel Practitioners syndromic surveillance component consists of more than 100 health care providers across Canada who report the proportion of patients seen in their clinic each week who had ILI symptoms.

The FluWatchers syndromic surveillance component consists of more than 1,000 volunteers across Canada who report each week if they experienced symptoms of an ILI via an online questionnaire.

Influenza-like-illness (ILI) definition:

Sudden onset of respiratory symptoms with fever and cough and with one or more of the following: sore throat, joint pain, muscle aches, or fatigue which is likely due to influenza. In children under 5 years of age, symptoms such as nausea, vomiting and diarrhea may also be present. In patients under 5 years of age or 65 years and older, fever may not be present.

4. Outbreak surveillance

Surveillance of the distribution of outbreaks by setting provides a timely, sensitive measure of early influenza activity and also provides an indicator of the burden of influenza within certain at-risk populations and settings.

Outbreaks of laboratory-confirmed influenza or ILI in different settings (long-term care facilities, nursing homes, acute care facilities, schools, daycares and remote and/or isolated communities) are reported from provinces and territories.

Outbreak definitions:
Setting Setting Definition Outbreak Definition

Long-Term Care Facilities, Nursing Homes:

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 where provincial/territorial public health is responsible for outbreak management under provincial legislation

Laboratory-confirmed influenza outbreak: two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case of influenza within a surveillance setting.

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).

Laboratory-confirmed influenza outbreak: two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case of influenza within a surveillance setting (e.g. floor, unit or ward).

Schools and Daycares:

Facilities that provide educational or childcare programs for children under the age of 18 years.

ILI outbreak in school: Greater than 10% absenteeism which is likely due to ILI.

Remote and/ or Isolated communities:

A community that is physically and/or socially separated from the surrounding population (e.g., communities that are geographically isolated due to limited transportation links,  communities whose members have very limited interactions outside their community).

Laboratory-confirmed influenza outbreak: Unusual or unexpected number of ILI cases in a seven day period including at least one laboratory confirmed case of influenza.

Other:

Any locations not identified on this list in which an outbreak of influenza or ILI occurs (e.g., retirement homes, assisted living or hospice settings, private hospitals/clinics, correctional facilities, colleges/universities, adult education centres, shelters, group homes, and workplaces)

Note: Specific to setting as determined by reporting province

Laboratory-confirmed influenza outbreak: two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case of influenza within a surveillance setting.

ILI outbreak: two or more cases of ILI within a seven-day period.

ILI outbreak in workplaces: Greater than 10% absenteeism which is likely due to ILI.

5. Severe outcomes surveillance

FluWatch assesses the burden and impact of seasonal influenza through this system component.
Hospitalizations and deaths of patients with influenza (confirmed by a laboratory test) are reported by provincial and territorial ministries of health and two hospital sentinel networks.

Provincial/Territorial influenza hospitalizations and deaths

Hospitalizations and deaths in children and adults with influenza are reported by 8 provincial and territorial ministries of health (excluding British Columbia, Nunavut, Ontario and Quebec). The hospitalization or death does not have to be directly caused by influenza; a positive laboratory test is sufficient for reporting. Only hospitalizations that require intensive medical care are reported by Saskatchewan.

Pediatric influenza hospitalizations and deaths

The Immunization Monitoring Program Active (IMPACT) network reports the weekly number of hospitalizations with influenza among children admitted to one of the 12 participating paediatric hospitals in 8 provinces. These sentinel hospitals represent a portion of all influenza-associated pediatric hospitalizations in Canada.

Adult influenza hospitalizations and deaths

The Canadian Immunization Research Network (CIRN) reports the weekly number of hospitalizations with influenza among adults admitted to one of at least 5 participating sentinel hospitals in Ontario, Quebec, British Columbia or Alberta, Saskatchewan or Manitoba, and an Atlantic province (i.e., New Brunswick or Newfoundland and Labrador or Prince Edward Island, or Nova Scotia). These sentinel hospitals represent a portion of all influenza-associated adult hospitalizations in Canada.

6. Influenza strain characterization and antiviral resistance testing

Through this surveillance component, FluWatch receives a weekly analysis from the National Microbiology Laboratory that identifies the specific strains of influenza that are circulating; compares them to the viruses contained in the seasonal influenza vaccine, and looks for resistance to antivirals used to treat influenza. Through this component, FluWatch also maintains the capacity to detect unusual strains of influenza or other emerging respiratory viruses.

Provincial public health laboratories grow the influenza virus from some specimens and send these viruses to the National Microbiology Laboratory for strain characterization and antiviral resistance testing. These represent a portion of all influenza positive tests in Canada. The proportion of viruses of each influenza type and subtype is not necessarily representative of viruses circulating in the community.

Identifying the specific influenza strain of each virus is done by looking at how well antibodies that recognize the influenza strains used in the vaccine will recognize the sample virus. The test used for antigenic strain characterization is the hemagglutination inhibition (HI) test. The genetic sequence of the viral hemagglutinin (HA) gene is also compared to the influenza strains used in the vaccine.

7. Vaccine monitoring

The FluWatch program introduced a vaccine monitoring component for the 2018/2019 influenza season. Through this surveillance component, FluWatch provides evidence to support public health interventions and their evaluation.  New indicators for vaccine coverage, effectiveness and links to vaccine safety surveillance are reported. Results of these surveillance indicators are included in the FluWatch report as they become available.

Vaccine coverage

The Public Health Agency of Canada conducts a National Influenza Immunization Coverage Survey to collect information on uptake of the influenza vaccine each season.

Vaccine effectiveness

FluWatch is building and supporting capacity to routinely monitor influenza vaccine effectiveness in community and hospital settings.
Provinces and Territories provide FluWatch with community-based surveillance data to estimate the effectiveness of the seasonal influenza vaccine among patients who seek medical care from sentinel primary care practitioners.  The Canadian Sentinel Practitioners Surveillance Network provides community-based estimates of the effectiveness of the seasonal influenza vaccine among patients who seek medical care from sentinel primary care practitioners.
The Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network provides estimates of the effectiveness of the seasonal influenza vaccine in preventing hospitalization.

Vaccine safety monitoring

The Public Health Agency of Canada monitors reports of adverse events following immunization (AEFI) for all vaccines, including the influenza vaccine.

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