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Infectious Diseases

COVID-19 Wastewater Surveillance

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Summary

  • The Ontario Science Advisory Table is sharing regional results of wastewater surveillance data on their Ontario COVID-19 dashboard. Recent results for the Central East region (which includes Simcoe Muskoka) showed an increase trend in the wastewater signal starting early March and peaking in late April, with levels well above those seen in December 2021 (peak of wave 5). The most recent data suggests a downward trend back toward the levels observed in early March.
  • The health unit has received results of genome sequencing of SARS-CoV-2 from wastewater surveillance. The Delta variant was the dominant VOC in samples from Barrie, Midland and Orillia in late November through mid-December. The Omicron variant dominated the wastewater signal in January and February in Barrie and Midland, with small proportions of the BA.2 sub-variant of Omicron becoming evident in the most recent samples from mid-February.
  • Recent samples collected in Barrie suggest transmission may be decreasing in this community.
  • The wastewater signals in Collingwood, Midland and Orillia appear to have reached their peak and begun to plateau, COVID-19 hospital admissions in these communities have stopped increasing as well.
  • Overall, wastewater signals have been variable within local communities with short term fluctuations in recent weeks.
  • There was a large spike in a recent sample from Collingwood. It is difficult to interpret individual samples in isolation; however, previous spikes in the wastewater signal in Collingwood have been accompanied by increases in the number of COVID-19 patients at the local hospital.
  • 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.

Wastewater SARS-CoV-2 signal trends

City of Barrie: wastewater viral signal and COVID-19 patients at Royal Victoria Hospital

Town of Collingwood: wastewater viral signal and COVID-19 patients at Collingwood General and Marine Hospital

Town of Midland: wastewater viral signal and COVID-19 patients at Georgian Bay General Hospital - Midland site

City of Orillia: wastewater viral signal and COVID-19 patients at Orillia Soldiers' Memorial Hospital

About Wastewater Surveillance

  • Wastewater sample collection in Collingwood has increased from once per week to three times per week starting the week of April 10, 2022. This increase sampling frequency will help us interpret trends in the wastewater signal in this community.
  • Samples are being collected five times per week in Barrie in 2022, an increase from the three times per week schedule in 2021.
  • 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.
  • 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 the number of COVID-19 admitted hospitalizations at Royal Victoria Regional Health Centre (Barrie), Collingwood General and Marine Hospital (Collingwood), Georgian Bay General Hospital (Midland) and Orillia Soldiers’ Memorial Hospital (Orillia). This includes both patients hospitalized because of COVID-19 (causal) and patients who are hospitalized and also have COVID-19 (incidental).
  • Hospital admissions data for COVID-19 patients is as reported by hospitals to the Ministry of Health, regardless of where the patient normally resides. Hospital catchment areas do not align directly with wastewater catchment areas. Royal Victoria Regional Health Centre in Barrie and Orillia Soldiers’ Memorial Hospital in Orillia are larger hospitals with more acute and ICU beds, and as such may receive a larger number of patients from communities further from the wastewater catchment. This may also include patients who are resident outside of the health unit region who would not be considered local cases. Similarly, the Town of Collingwood represents approximately one-third of the local South Georgian Bay population served by Collingwood General and Marine Hospital. The comparison of bed census data (COVID-19 patients in hospital) should be considered with this in mind.
  • 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.
  • 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.