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COVID-19 Wastewater Surveillance in Ontario

COVID-19 Wastewater Surveillance in Ontario

Wastewater surveillance is used by public health experts to track and monitor diseases, including COVID-19. This is done by testing community wastewater for the presence of SARS-CoV-2 from infected individuals —called the wastewater signal. This report presents the wastewater signal for Ontario, as well as its sub-regions.

Acknowledgement: The COVID-19 Wastewater Surveillance in Ontario report is based on the original work of the Ontario COVID-19 Science Advisory Table entitled, Wastewater Signals in Ontario, September 6, 2022.

Updates to COVID-19 Wastewater Surveillance Report as of April 13, 2023:

The COVID-19 Wastewater Surveillance in Ontario report has been updated to align with the Government of Ontario’s changes to the Wastewater Surveillance Initiative's sampling location strategy and updates to PHO’s analytic approach including:

  • A change in statistical software used to run the analysis to a more flexible and sustainable system
  • Changing the population source used to weight the signals from the entire public health unit population to sewershed populations.

As a result, there may be changes to how the wastewater graphs are presented.

Learn more about these updates

This is a line graph of the estimated COVID-19 wastewater signal for Ontario. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Wastewater signals peaked in early January 2022 (wave 5), mid-April 2022 (wave 6), and mid- to late-July 2022 (wave 7). Wastewater signals began slowly increasing in mid-September.

This report is updated Thursdays at 4:30 p.m. ET (based on data extracted on Wednesdays)

For information on source data, citations, definitions, methods and more see our Technical Notes.

To view an archived version of the report, see Archived Graphs.

This is a line graph of the estimated COVID-19 wastewater signal for the North region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Wastewater signals peaked twice during wave 5, in early January 2022 and in early February 2022. Signals peaked again in mid-April 2022 (wave 6) and late July 2022 (wave 7). Wastewater signals began slowly increasing in mid-September 2022.

This is a line graph of the estimated COVID-19 wastewater signal for the North region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Wastewater signals peaked twice during wave 5, in early January 2022 and in early February 2022. Signals peaked again in mid-April 2022 (wave 6) and late July 2022 (wave 7). Wastewater signals began slowly increasing in mid-September 2022.

This is a line graph of the estimated COVID-19 wastewater signal for the Eastern region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Wastewater signals peaked in early January 2022 (wave 5), mid-April 2022 (wave 6), and late July 2022 (wave 7). Wastewater signals fluctuated through August and September 2022, then peaked again in early October 2022.

This is a line graph of the estimated COVID-19 wastewater signal for the Central East (excluding the GTA) region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Estimates highlighted with a grey background, covering the most recent three weeks, are more likely to change. Wastewater signals peaked in April 2022, and September 2022. A smaller wastewater signal peak occurred in December 2022. Wastewater signals appear to be declining until mid-January.

This is a line graph of the estimated COVID-19 wastewater signal for the GTA region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Wastewater signals peaked in early January 2022 (wave 5), in early April 2022 (wave 6), and mid-July 2022 (wave 7). Wastewater signals began increasing in mid-September.

This is a line graph of the estimated COVID-19 wastewater signal for the South West region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Wastewater signals peaked in mid-January 2022 (wave 5), mid-April 2022 (wave 6). Wave 7 has seen three smaller peaks, in early August, early September, and late September 2022.

This is a line graph of the estimated COVID-19 wastewater signal for the Central West (excluding the GTA) region. On the X axis is sample date. On the Y axis is standardized concentration of SARS-CoV-2 Gene Copies. Wastewater signals peaked in mid-January 2022 (wave 5), mid-April 2022 (wave 6), and from mid- to late-July 2022 (wave 7). Wastewater signals have fluctuated since August 2022, with a small peak apparent peak in mid-September 2022 before declining until mid-October. Wastewater signal have been increasing since mid-October.

Grey Background: The dotted portion of the curves highlighted with a grey background should be interpreted with caution. These estimates have a higher likelihood of changing in future updates due to a combination of reasons, including but not limited to the analytical approach used, new data submissions for recent days or updates to previously reported data.

Ontario sub-regions: These refer to the following geographical groupings of public health units:

  • North West: Northwestern Health Unit and Thunder Bay District Health Unit.
  • North East: Algoma Public Health; North Bay Parry Sound District Health Unit; Porcupine Health Unit; Public Health Sudbury & Districts; and Timiskaming Health Unit.
  • Eastern: Eastern Ontario Health Unit; Hastings Prince Edward Public Health; Kingston, Frontenac and Lennox & Addington Public Health; Leeds, Grenville & Lanark District Public Health; Ottawa Public Health; and Renfrew County and District Health Unit.
  • Central East, excluding GTA: Haliburton, Kawartha, and Pine Ridge District Health Unit; Peterborough Public Health; and Simcoe Muskoka District Health Unit.
  • Greater Toronto Area (GTA): Durham Region Health Department; Halton Region Public Health; Peel Public Health; Toronto Public Health; and York Region Public Health
  • South West: Chatham-Kent Public Health; Grey Bruce Health Unit; Huron Perth Public Health; Lambton Public Health; Middlesex-London Health Unit; Southwestern Public Health; and Windsor-Essex County Health Unit.
  • Central West, excluding GTA: Brant County Health Unit; Haldimand-Norfolk Health Unit; City of Hamilton Public Health Services; Niagara Region Public Health; Region of Waterloo Public Health and Emergency Services; and Wellington-Dufferin-Guelph Public Health.

How to cite this page: Ontario Agency for Health Protection and Promotion (Public Health Ontario). COVID-19 wastewater surveillance in Ontario. Toronto, ON: King's Printer for Ontario; 2023.

Updated 1 June 2023
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