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Infectious Diseases

COVID-19 Wastewater Surveillance

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Summary

  • Public Health Ontario is sharing data for COVID-19 Wastewater Surveillance in Ontario. The Central East region (which includes Simcoe Muskoka) wastewater signal is showing a decreasing trend since late January.
  • There are no significant trends in the wastewater signals in Barrie, Bracebridge, Collingwood, or Midland.
  • There is a significant decreasing trend in Orillia and Penetanguishene. This follows an elevated signal in Penetanguishene in early March.
  • There was one sample from Barrie last week with elevated levels, but subsequent samples have returned to a lower level consistent with previous between-wave troughs.
  • The BA.5 subvariant of Omicron (and its sublineages) was the dominant variant detected in wastewater samples across local sites through the second half of 2022. The proportion of BA.5 (and its sublineages) detected in our samples has been decreasing since early January, and is non-detectable across most sites in recent samples. Recent evidence suggests other subvariants are currently dominant across the province. 
  • Signals in wastewater may act as a lead indicator for changes in community infection levels, however, given the overall variability it is unclear how strong of a predictor wastewater surveillance for COVID-19 is. In many sewersheds where wastewater surveillance is performed, changes in wastewater levels can give 5-10 days warning before changes in reported cases are seen, although this is not always the case.
  • Hospital admissions can be expected to peak later than increases in community transmission, as there is a delay between initial infection (and beginning of shedding into wastewater) and development of infection severe enough to require hospitalization. This may be less evident in smaller communities with fewer hospitalizations.

Wastewater SARS-CoV-2 signal trends

City of Barrie: wastewater viral signal and COVID-19 Hospitalizations among Barrie residents

Town of Bracebridge: wastewater viral signal and COVID-19 hospitalizations among Bracebridge residents

Town of Collingwood: wastewater viral signal and COVID-19 hospitalizations among Collingwood residents

Town of Midland: wastewater viral signal and COVID-19 hospitalizations among Midland residents
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City of Orillia: wastewater viral signal and COVID-19 hospitalizations among Orillia residents

Town of Penetanguishene: wastewater viral signals and COVID-19 hospitalizations among Penetanguishene residents

About Wastewater Surveillance

  • People with COVID-19 infection can shed SARS-CoV-2 virus RNA in their stool. This shedding occurs in people with and without symptoms, although the amount can vary from person to person.
  • Levels of SARS-CoV-2 viral RNA in wastewater can be measured to estimate patterns of COVID-19 infection in the community, whether or not people receive a COVID-19 test or are diagnosed with COVID-19 infection. This can help us understand COVID-19 transmission in the community, in conjunction with other public health data such as COVID-19 testing, reported cases, hospitalizations and outbreaks.
  • We are continually learning more about wastewater surveillance for COVID-19, sampling strategies and testing methods, and how the results can be used as a tool for public health. This is a rapidly evolving field, and there are still many unknowns in how to interpret the connection between SARS-CoV-2 in wastewater and COVID-19 infection in the community.
  • Wastewater surveillance for COVID-19 is being conducted at six local wastewater treatment plants in Barrie, Bracebridge, Collingwood, Midland, Orillia and Penetanguishene under the Ontario Ministry of the Environment, Conservation and Parks Wastewater Surveillance Initiative and in conjunction with Ontario Tech University.
  • Samples collected from participating wastewater treatment plants are analyzed by Ontario Tech University to detect viral RNA fragments from the SARS-CoV-2 virus responsible for COVID-19 infection.
  • Concentrations of Pepper Mild Mottle Virus (PPMoV) in wastewater are used to normalize the viral RNA levels detected in wastewater. The PPMoV virus is harmless and is commonly shed by humans. It helps us to understand the proportion of wastewater from human (fecal) waste compared to other sources such as kitchen water or commercial input.
  • Given changes to the provincial COVID-19 testing strategy and to case management, locally reported cases by residence no longer provides an accurate picture of community transmission.
  • Raw and normalized SARS-CoV-2 RNA levels in wastewater are now compared against patients hospitalized with COVID-19 from participating communities. This includes cases among local residents who are admitted to hospitals outside of our local area. This represents patients hospitalized because of COVID-19 (causal) and excludes patients who are hospitalized who also have COVID-19 (incidental)
  • Increases in SARS-CoV-2 RNA levels in wastewater over multiple samples may indicate increasing transmission within the community, while individual samples with unusually high levels are likely to be outliers.
  • The ability of wastewater surveillance to represent residents of a community is impacted by the ways in which people travel in and out of these communities for work and leisure.
  • The sewersheds sampled cover the majority of residents of participating communities, however, samples collected at the wastewater treatment plants may also include inputs from other sources, such as from septic tanks in neighbouring communities.
  • Absolute levels of SARS-CoV-2 RNA virus in wastewater are not comparable across municipal sewersheds due to the differences in the systems themselves, including the inputs into the system (residential, industrial, commercial), the population served, the distance wastewater travels to reach the treatment plant, and physical components of the wastewater systems.Results should only be compared within each system to understand patterns or trends.
  • Please note that during summer 2021, there was a decrease in Pepper Mild Mottle Virus (PPMoV) levels. It is unclear whether this reflected changes in what is moving through the wastewater system, or whether it was related to other environmental impacts. The normalized viral RNA signal should be interpreted with caution, as shifts in the normalized signal may not represent shifts in SARS-CoV-2 viral RNA levels. As a result, the raw viral data is presented first, rather than the normalized viral signal.
  • Emerging research suggests that in wastewater plants that serve smaller communities (such as Midland and Collingwood), a higher level of infection in the community is required to detect SARS-CoV-2 patterns in wastewater samples.

Technical Notes and Definitions

Please see Technical Notes and Definitions here.

For more information about wastewater surveillance:

Last Updated: March 23, 2023