Ontario Influenza Bulletins

Ontario Influenza Bulletins from 2011 onward can be found on Public Health Ontario's Influenza Bulletin page.

Ontario Influenza Bulletins prior to 2011 can be found in the Public Health Commons collaboration community located on the portal (requires login). You must be employed by a public health unit to access to Public Health Commons. If you are employed by a public health unit and require a password and username for Public Health Commons, please contact

If you are not employed by a public health unit and would like access to an archived flu bulletin, please contact

These publications are available in English only due to their technical nature. To obtain more information, please contact ServiceOntario INFOline.

Influenza has been a reportable disease in Ontario since 1923. A highly contagious acute viral disease of the respiratory tract, influenza continues to be a major cause of preventable morbidity and mortality in Ontario. Influenza viruses are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness. It is estimated that annually influenza and community-acquired pneumonia account for 60,000 hospitalizations and 8,000 deaths, most of which occur among elderly persons1. Groups at increased risk for influenza complications include the elderly, immuno-compromised and persons with chronic medical conditions. In Canada, on average, 500-1,500 deaths every year are due to influenza alone. Annual incidence rates in Canada range from 10 to 20 per cent each year and can be considerably higher in epidemics. Current control measures in Canada include vaccination and chemoprophylaxis with anti-virals. The antigenic characteristics of the circulating strains provide the basis for selecting the strains that are included in the annual influenza vaccine.

Definitions for Influenza Activity Levels

*Confirmation of influenza within the surveillance region at any time within the prior week
†Sub-regions within the province or territory as defined by the provincial/territorial epidemiologist

Influenza-Like Illness (ILI) Definitions :

A) ILI in the general population :
Acute onset of respiratory illness with fever and cough, and with one or more of the following-- sore throat, arthralgia, myalgia, or prostration which could be due to influenza virus. In children under 5, gastrointestinal symptoms may also be present. In patients under 5 or 65 and older, fever may not be prominent.

B) ILI/Influenza outbreaks:
Schools and work sites : greater than 10% absenteeism on any day, most likely due to ILI.
Residential institutions : two or more cases of ILI within a seven-day period, including at least one laboratory-confirmed case.

For More Information

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