Influenza is a disease caused by the influenza virus. Symptoms of influenza include sudden onset of headache, chills and cough followed by a fever, appetite loss, muscle aches and tiredness. Influenza is a cause of outbreaks in long-term care homes. For more information, see the health unit's fact sheet on "Influenza".
Influenza surveillance begins on September 1 each year and ends on August 31 of the following year. The majority of influenza cases occur between November and April. From November to April, a weekly bulletin is released by the health unit. For the most recent weekly flu bulletin, see the health unit’s respiratory virus surveillance webpage.
Influenza vaccines are available to protect again some of the strains of influenza.
For more information, see the health unit’s fact sheets on the flu vaccine for both adults and children.
Simcoe Muskoka
Ontario
By Age Group
By Sex
Technical Notes
The following graph shows the number of influenza cases in Simcoe Muskoka between 1999-00 and 2021-2022. There have been between 28 and 949 influenza cases every season since 1999-00, excluding 2020-21 season. Where zero local cases were reported despite conducting almost 500 tests for influenza. In 2021-22 season, 38 cases of influenza were reported in Simcoe Muskoka.
While cases of influenza A and influenza B are generally reported every year, influenza A is usually the main circulating subtype. Influenza B made up a larger percentage of cases in the 2011-12, 2013-14 and 2016-17 seasons. In the 2021-22 flu season, 100% of influenza cases in Simcoe Muskoka were influenza A.
The following graph shows the incidence rate of influenza in Simcoe Muskoka and Ontario between 1999-00 and 2021-22. The Simcoe Muskoka rate is comparable to the Ontario rate. However, the six consecutive seasons prior to the pandemic had higher rates locally than at the provincial level. There are many factors that affect the number of reported influenza cases. For the 2021-22 flu season, the Simcoe Muskoka rate was 5.8 cases per 100,000 population and the Ontario rate was 11.4 cases per 100,000 population.
By Age Group
The following graphs shows the breakdown of influenza cases across age groups as well as the age-specific incidence rate of influenza in Simcoe Muskoka between 1999-2000 and 2021-22. The age-specific rates are influenced by which subtype and strains of influenza are circulating in each season. For example, the dominant strain in the 2014-15, 2016-17 and 2017-18 seasons was influenza A(H3N2) which generally infects and affects people who are 75 years and older more severely. In the 2019-20 season, both H1N1 and H3N2 strains of influenza circulated, affecting both the very young and old, as well as middle-aged populations. The number of influenza cases in 2021-22 season was very low, making it difficult to interpret age-trends.
By Sex
The following graph shows the sex-specific incidence rate of influenza in Simcoe Muskoka and Ontario between 2005-06 and 2021-22. The incidence rate of influenza is similar for males and females. The increased incidence in females in 2014-15, 2016-17 and 2017-18 is likely because females make up a larger proportion of older adults. The dominant strain in the 2014-15, 2016-17 and 2017-18 seasons was influenza A(H3N2) which generally infects and affects people who are 75 years and older more severely.
More detailed data for Ontario and each health unit can be found on Public Health Ontario’s interactive Reportable Disease Trends in Ontario tool.
Technical Notes
There are many factors that influence how many cases are reported to the health unit, as explained on the Infectious Diseases page.
It is unclear to what extent the global COVID-19 pandemic has influenced the reporting and spread of other infectious diseases - counts and rates of disease since 2020 should be interpreted with caution.
Page last updated October 25, 2022