Map of Simcoe Muskoka

Infectious Diseases

Influenza (the 'flu')

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 "Cold vs. Flu".

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 flu 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

Simcoe Muskoka

The following graph shows the number of influenza cases in Simcoe Muskoka between 1999-00 and 2018-19. There have been between 28 and 949 influenza cases every season since 1999-00. In the 2018-19 flu season, 712 cases of flu were reported in Simcoe Muskoka.  Increased testing and more sensitive tests may partially explain the increased incidence in recent years.

Influenza_Counts

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 flu season and the 2013-14 season. In the 2017-18 flu season, 59% (564) of influenza cases in Simcoe Muskoka were influenza A, while 41% (385 cases) of influenza cases were influenza B.  The 2018-19 flu season saw influenza A as the main circulating strain.

20150831InfluenzaCasesSubTypeSimcoeMuskoka

Ontario

The following graph shows the incidence rate of influenza in Simcoe Muskoka and Ontario between 1999-00 and 2018-19. The Simcoe Muskoka rate is comparable to the Ontario rate. However, the five most recent seasons have had higher rates locally than at the provincial level. There are many factors that affect the number of reported influenza cases. For the 2018-19 flu season, the Simcoe Muskoka rate was 121.9 cases per 100,000 population and the Ontario rate was 90.9 cases per 100,000 population.

Influenza_Rates

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 2018-19. 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 2018-19 season, both H1N1 and H3N2 strains of influenza circulated, affecting both the very young and old, as well as middle-aged populations.
inf_agegroup

20150831InfluenzaAgeSpecificRateSimcoeMuskoka

By Sex

The following graph shows the sex-specific incidence rate of influenza in Simcoe Muskoka and Ontario between 2005-06 and 2018-19. 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.

20150831InfluenzaSexSpecificRateSimcoeMuskoka

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.