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Infectious Diseases

COVID-19 Wastewater Surveillance

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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 four local wastewater treatment plants in Barrie, Collingwood, Midland and Orillia 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.
  • Normalized and raw SARS-CoV-2 levels in wastewater are compared against COVID-19 cases reported among people residing in the communities of Barrie, Collingwood, Midland and Orillia, by symptom onset date and reported date.Symptom onset date more closely approximates the date of infection and therefore transmission patterns compared to reported date which represents the date that a case became known to public health.
  • 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.
  • 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.
  • 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.

Summary

  • Recent wastewater data support information from reported cases of COVID-19, showing sustained low levels of COVID-19 infection through the summer and increasing cases over recent weeks.
  • Since late July there have been increases in reported cases in Barrie and Orillia, accompanied by slight increases in SARS-C0V-2 wastwater signal.
  • In early September, both Collingwood and Midland have seen incrases in both community cases and wastwater SARS-C0V-2 levels.
  • Signals in wastewater may act as a lead indicator for changes in community infection levels, however, given the overall variability and the low number of cases in Collingwood, Midland and Orillia 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.
  • Changes in wastewater viral RNA signals in Collingwood, Midland and Orillia should be interpreted with caution as viral RNA levels in these regions are near the lower level of detection of the viral RNA test.
  • Short-term changes in wastewater viral RNA signals may not always correspond to changes in reported COVID-19 cases in the community. This can be seen in late May in Barrie, where one unusually high sampling day suggests a spike that was not reflected in an increased case count.
  • Please note that in the more recent data, there has been a decrease in Pepper Mild Mottle Virus (PPMoV) levels. It is unclear at this time whether this reflects changes in what is moving through the wastewater system, or whether it is 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.
  • Due this combination of low PPMoV levels and low SARS-CoV-2 viral RNA levels, the raw viral data is presented first, rather than the normalized viral signal.

City of Barrie: wastewater viral signal and reported COVID-19 cases

Town of Collingwood: wastewater viral signal and reported COVID-19 cases

Town of Midland: wastewater viral signal and reported COVID-19 cases

City of Orillia: wastewater viral signal and reported COVID-19 cases