Overview of influenza monitoring in Canada

FluWatch is Canada's national surveillance system that monitors the spread of the flu and other flu-like illnesses on an ongoing basis. Flu reports that contain information on flu activity in Canada are posted online every Friday.

On this page

• Program objectives
• Seven components of influenza surveillance in Canada
  1. Geographic Spread of Influenza/Influenza-like Illness Activity
  2. Laboratory-Confirmed Detections
  3. Syndromic Surveillance
  4. Outbreak Surveillance
  5. Severe Outcomes Surveillance
  6. Strain Characterization and Antiviral Resistance Testing
  7. Vaccine Monitoring
• Definitions

Program objectives

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

• Detect: to detect and respond to outbreaks and other events of public health concern.
• Inform: to use the data and information to create, improve and apply to public health programs and policies to control the flu.
• Enable: to make sure that the information gathered on the flu in Canada supports international flu monitoring and is ready in case of a global outbreak. 

Seven parts of flu monitoring in Canada

1. Geographic spread of Flu and ILI activity

FluWatch keeps track of when and where flu and ILI is happening across Canada, and describes the groups of people that are being affected the most.

The level of flu or ILI activity for each region is determined by provincial and territorial ministries of health. The activity level assigned is based on lab confirmations of the flu, as well as increases in health care visits for flu or ILI and reported outbreak. Flu surveillance regions within the province or territory are defined by provincial and territorial ministries of health.

2. Laboratory-confirmed detections

FluWatch analyses the pattern of flu circulation in Canada, to determine the start, peak and end of the flu season, by tracking lab test results.

Provincial, regional and some hospital labs report the number of tests that doctors request each week and the number of positive tests for the flu virus (influenza) or other respiratory viruses. Flu tests for patients in the territories are sent to reference labs in the province to get the results.

Provincial public health labs send information to FluWatch on the age and sex of patients with a positive flu test for cases of the flu in order to monitor the impact of the flu in different age-groups. This case-level data represents a portion of laboratory-confirmed flu detections.

3. Syndromic surveillance

FluWatch gathers and uses flu and ILI data to look for signals of high or unusual flu activity and outbreaks by analysing the pattern of the flu in Canada. This process is called syndromic surveillance.

Syndromic surveillance can detect signals of higher levels of flu activity early (before flu cases get confirmed and reported to public health agencies).

The Sentinel Practitioners syndromic surveillance part of FluWatch is made up of more than 100 health care providers across Canada who report the proportion of patients seen in their clinic each week with flu-like symptoms.

The FluWatchers syndromic surveillance part of FluWatch is made up of more than 1,000 volunteers across Canada who report each week if they had any flu-like symptoms with an online questionnaire. Anyone in Canada can be a volunteer FluWatcher!

Visit our FluWatchers page for more info and to sign up. 

4. Outbreak surveillance

Tracking where and when outbreaks happen provides a timely, sensitive measure of early flu activity. It also provides an indicator of the burden of flu within certain at-risk groups 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.

5. Severe outcomes surveillance

FluWatch assesses the seriousness, impact and burden of seasonal flu through severe outcome surveillance.

The number of deaths due to the flu and number of people admitted to hospital with the flu (lab-confirmed cases) are reported by provincial and territorial ministries of health as well as 2 hospital networks that monitor severe outcomes due to the flu.

Provincial/Territorial flu hospitalizations and deaths

Each week, 9 provincial/territorial ministries of health (excluding British Columbia, Nunavut, Ontario and Québec) report the number of children and adults admitted to hospital due to the flu and the number of deaths caused by the flu to FluWatch.

Hospital admissions and/or deaths don’t have to be directly caused by the flu; a positive lab test is enough to be reported.

Only hospital admissions that need intensive medical care are reported by Saskatchewan.

Pediatric flu hospitalizations and deaths

Each week, the Immunization Monitoring Program Active (IMPACT) network reports the number of children admitted to hospital with the flu (paediatric cases) to FluWatch

Twelve paediatric hospitals across 8 provinces are part of the IMPACT network. These hospitals monitor for the flu by reporting the number of paediatric cases of the flu.

The number of children admitted to hospital with the flu reported by the IMPACT network represent a portion of all flu-related paediatric hospital admissions in Canada.

Adult flu hospitalizations and deaths

The Canadian Immunization Research Network (CIRN) reports the number of adults admitted to the hospital with the flu each week from participating hospitals across Canada.

The number of adults admitted to the hospital with the flu reported by participating hospitals represents a portion of all flu-related adult hospital admissions in Canada.

6. Flu strain characterization and antiviral resistance testing

There are hundreds of different strains of the flu virus that can infect people. These are classified into 2 main types: influenza A and B.

Other types of the flu virus like influenza C and D, may cause very mild illness or do not infect people at all.

Influenza A viruses can also be classified into subtypes, like H1N1, and influenza B viruses can be classified by lineages, like Yamagata lineage (origin of the virus).

FluWatch receives information each week from the National Microbiology Laboratory on:

• the specific strains of the flu virus (influenza) that are circulating in people in Canada
• how those strains compare to the flu viruses that the seasonal flu shot can protect against
• whether circulating strains are resistant to the antiviral medicines that doctors prescribe to prevent and treat flu

With this information, FluWatch is able to detect unusual strains and changes in the flu virus.

Provincial public health labs grow the flu viruses from patient samples and send them to the National Microbiology Laboratory for the strains to be identified and tested against the antivirals that prevent and treat the flu.

These represent a portion of all positive flu tests in Canada.

The proportion of each flu type and subtype is a good indicator of which flu viruses are circulating in Canada during each flu season, but they are not always perfectly representative.

Identifying the specific flu strain of each virus is done by looking at how well antibodies that recognize the flu strains used in the vaccine (flu shot) will recognize the sample virus.

The test used for antigenic strain characterization is the hemagglutination inhibition (HI) test. The genetic sequence of the flu virus’s hemagglutinin (HA) gene is also compared to the flu strains used in the vaccine (flu shot).

7. Vaccine (flu shot) monitoring

The FluWatch program introduced a vaccine monitoring component for the 2018/2019 flu season. Through this monitoring, FluWatch provides evidence to support public health interventions and their evaluation.  Results of monitoring activities related to vaccine coverage and effectiveness are included in the FluWatch reports.

The Public Health Agency of Canada also keeps track of adverse events following immunization (AEFI) for all vaccines, including the flu vaccine. These data are not included in the weekly FluWatch report. However, more information about this surveillance program can be found here.

Vaccine (Flu shot) coverage

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

Vaccine effectiveness

FluWatch is building and supporting capacity to routinely monitor influenza vaccine effectiveness in community and hospital settings.

Vaccine effectiveness is a measure of how well the flu vaccine is able to prevent the flu. Throughout the flu season, surveillance networks estimate how well the flu vaccine is working. Estimates can vary depending on things like the study methods; the population, setting and outcomes that are being studied; the type and mix of vaccine products; the stage of the season and the kinds of flu viruses that are circulating when the study is conducted.

The Canadian Sentinel Practitioners Surveillance Network (SPSN) provides estimates of how well the flu shot is able to prevent primary care visits for the flu.

The Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network estimates how effective the seasonal flu shot is in preventing hospitalization in adults.

Definitions

The flu

A sudden illness with fever and cough that happens when your respiratory system—your nose, throat and lungs—get infected with a virus called influenza virus.

• It can happen over a short period of 2 days or less.
• Influenza is commonly called the “flu” and it is not the same as the “stomach flu” which has different symptoms and is caused by different viruses. 

Influenza

The name of the flu virus.

Flu-like illness

The sudden onset (over 2 days or less) of flu symptoms with fever and cough and with one or more of the following: sore throat, joint pain, muscle aches, or fatigue that is likely due to the flu, but not confirmed by a lab test. This is referred to as ILI (“influenza-like illness”).

ILI

Short form for “influenza-like illness”.