COVID-19 Wastewater Surveillance in Ontario

The COVID-19 Wastewater Surveillance in Ontario report is updated Fridays at 11:30 a.m.

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.

This report provides an overview of COVID-19 wastewater signals in Ontario and 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.

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).

The province-wide COVID-19 wastewater signal for Ontario is a weighted mean of standardized, biomarker-normalized concentrations of SARS-CoV-2 gene copies across 103 wastewater treatment plants, pumping stations and sewersheds in the 34 public health units. Each series of concentrations of N1 and N2 genes found in the wastewater of each location was standardized using the gene and location specific standard deviation. Standardized concentrations of N1 and N2 genes were first converted to standard deviation units and then log transformed. Restricted cubic splines with knots located every 10 days were fitted separately for each gene in each location to estimate daily log transformed standardized values.

Fixed-effects meta-analyses were used to calculate daily inverse-variance weighted means of log transformed estimates within each public health unit. Daily inverse-variance weighted means were then combined in a fixed-effects analysis across public health units using population size of public health units as analytical weight. Resulting daily weighted means were exponentiated and therefore represent standard deviation units.

*The dotted orange line and the lighter shaded area represent incomplete data (less than 90% of data available on a given date). The line thus represents the currently available best estimates using the statistical approaches above to account for not yet available data, but are provisional. As such they may be under- or over-estimates and may change when more data become available.

To account for the proportion of the wastewater that is from humans and the proportion that is rain water, snow melt, etc., N1 and N2 gene concentrations are normalized using the seasonally stable fecal biomarker pepper mild mottle virus (PMMoV). Samples are typically taken 3 times per week at each location. There is a 5 to 7 day lag between the detection of SARS-CoV-2 gene copies in the wastewater, and the diagnosis and reporting of COVID-19 cases. The wastewater signal on January 21, for example, is reflected in reported COVID-19 cases around January 26 to 28.

The data is extracted weekly at 1PM on Wednesdays.

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).

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. 

Wastewater signals peaked in early January 2022 (wave 5), mid-April 2022 (wave 6), and mid-August 2022 (wave 7).

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).

 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), and early August 2022 (wave 7). Signals decreased from early August to mid-August before increasing again to a plateau from early September.

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).

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).

See notes under province-wide figure for explanations of the methods used to derive region specific COVID-19 wastewater signals.

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

*The dotted orange line and the lighter shaded area represent incomplete data (less than 90% of data available on a given date). The line thus represents the currently available best estimates using the statistical approaches above to account for not yet available data, but are provisional. As such they may be under- or over-estimates and may change when more data become available.

Data sources include but are not limited to:
Ontario. Ministry of Environment, Conservation, and Parks. Ontario – extended aggregated WSI dataset [unpublished data table]. Toronto, ON: King’s Printer for Ontario; 2022.

Jüni P, da Costa BR, Maltsev A, Katz GM, Perkhun A, Yan S, et al. Briefs of the Ontario COVID-19 Science Advisory Table: Ontario dashboard: tracking Omicron [Internet]. Toronto, ON: Ontario COVID-19 Science Advisory Table; 2021 [cited 2022 Sep 4]. Available from: https://doi.org/10.47326/ocsat.dashboard.2021.1.0

Ontario’s wastewater surveillance is coordinated and hosted by the Ministry of the Environment, Conservation and Parks. Laboratory analyses are done by Carleton University, University of Guelph, Health Sciences North Research Institute, McMaster University, National Microbiology Laboratory, Ontario Tech University, University of Ottawa, Queen’s University, Ryerson University, University of Toronto, Trent University, University of Waterloo, University of Western Ontario and University of Windsor.

The data used to produce the wastewater signal graphs is based on the latest available data but may be subject to change due to:

  • Incorporation of newly received results that were not available in previous weeks due to occasional shipping and laboratory processing delays. This may result in minor virus signal changes compared to previous weeks. 
  • Revisions to previously submitted data. Examples include updates to analytical methods made at testing laboratories and re-processing of previously tested samples.

 

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; 2022. 

Updated 30 Sep 2022