Today, Toronto Public Health (TPH) has made wastewater surveillance data available to the public as part of its regular COVID-19 surveillance reporting. Wastewater surveillance data for Toronto is now available on the City of Toronto’s COVID-19: Wastewater Surveillance webpage.
TPH monitors COVID-19 activity in the community using a number of different data sources. With recent changes to the provincial testing strategy, TPH has reviewed the use of additional sources of data to better understand the changes in COVID-19 activity. Wastewater surveillance involves testing for the virus in sewage and monitoring changes over time, which can help TPH understand the presence of COVID-19 in a community independent of other methods of COVID-19 testing.
Ontario’s wastewater surveillance is coordinated and hosted by the Ministry of the Environment, Conservation and Parks (MECP). Ryerson University and the University of Toronto complete laboratory analyses on wastewater samples collected by the City. The wastewater surveillance data on the City’s website are analyzed at the provincial level through MECP, who then summarizes the data from the four wastewater treatment plants in Toronto. TPH will update the wastewater surveillance report on Wednesdays.
Wastewater surveillance is a relatively novel way to confirm community trends of COVID-19. It is particularly useful when access to PCR testing is limited, and captures virus that is shed from people both with and without symptoms. This method of surveillance is relatively new and is being implemented in many places around the world such as Ottawa, Vancouver, the United States, France, Spain and Australia.
As with any source of data, there are some limitations to consider. There can be variation in the wastewater data due to environmental factors which can affect the wastewater samples. There is also a large variation in the proportion of Toronto’s population that each wastewater treatment plant serves. Combined with environmental factors, this may dilute or concentrate the amount of virus that is detected.
Wastewater surveillance does not replace traditional COVID-19 testing, but can provide a broader understanding of COVID-19 activity.
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