Legionellosis is a disease caused by the bacteria Legionella pneumophila. There are two distinct illnesses: Pontiac fever (a milder illness) and Legionnaires’ disease (a more severe illness). Symptoms of both can include fever, headache, pain in one or more muscle groups, loss of appetite, and a general sense of not feeling well. Abdominal pain and diarrhea may also occur. The most severe cases of Legionnaires’ disease can develop pneumonia which can lead to death. Legionellosis most commonly affects people over 50 years old, people with compromised immune systems and/or who have chronic lung disease.
Legionellosis is not spread from person to person. Legionella bacteria are found naturally in the environment, usually in water, including hot water tanks, air conditioning cooling towers, humidifiers, whirlpools, spas, hot tubs and decorative fountains. People are exposed to the bacteria when they breathe in air with small droplets of water that have been contaminated. It is not spread by drinking contaminated water. For more information, see the health unit’s fact sheet on legionellosis.
Simcoe Muskoka
Ontario
Technical Notes
Simcoe Muskoka
The following graph shows the number of legionellosis cases in Simcoe Muskoka between 2000 and 2021. There have been between zero and twenty cases of legionellosis every year in Simcoe Muskoka since 2000. In 2021, 10 cases of legionellosis were reported in Simcoe Muskoka.
The increase observed in 2019 was due to local outbreaks.
Ontario
The following graph shows the incidence rate of legionellosis in Simcoe Muskoka and Ontario between 2000 and 2021. The Ontario rate increased by an average of 40% each year between 2009 and 2013. Clusters of cases were identified in the Greater Toronto Area in 2006, 2008 and 2010. The environmental source of contamination is rarely identified. Simcoe Muskoka has also had more cases in recent years with no common sources identified. Changes in testing protocols and weather patterns may also play a role in legionellosis incidence rates. In 2021, the Simcoe Muskoka rate was 1.6 cases per 100,000 population and the Ontario rate was 2.7 cases per 100,000 population.
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 August 19, 2022