Influenza (the flu) causes significant societal and healthcare burdens: it can rapidly spread and cause severe illness, exacerbate underlying medical conditions, and lead to hospitalization and death, especially among the youngest and oldest populations (see Note to readers).
Since 2020, Statistics Canada and the National Microbiology Laboratory from the Public Health Agency of Canada have been collaborating on the Canadian Wastewater Survey to monitor the spread of SARS-CoV-2 in participating cities across Canada. Testing for influenza and the respiratory syncytial virus (RSV) were added in 2022 to monitor trends and provide insights into recent flu seasons in selected cities. This includes both influenza A and B, the main influenza viruses that cause the seasonal outbreaks in humans.
The influenza season is a period with elevated influenza activity. The start of influenza season is declared when the percentage of positive laboratory tests on individuals potentially affected by influenza is above 5%. According to the Public Health Agency of Canada (see Note to readers), the current flu season started nationwide on the last week of November 2023, a bit ahead of the previous season.
The results of the wastewater analysis show that while all participating cities observed elevated flu levels at some point over the course of the winter of 2023-2024, they did not occur at the same time across cities or for the same duration. Flu A and flu B started circulating at sustained high levels earlier in the West of the country, first in Edmonton, and later moved East to Montréal and Halifax. Levels of flu A were consistently high although variable for longer stretches of time in Metro Vancouver and Toronto than in the other cities.
Contact information
For more information, or to enquire about the concepts, methods or data quality of this release, contact us (toll-free 1-800-263-1136; 514-283-8300; infostats@statcan.gc.ca) or Media Relations (statcan.mediahotline-ligneinfomedias.statcan@statcan.gc.ca).