University of Saskatchewan (USask) researchers in partnership with the City of Saskatoon and the Saskatchewan Health Authority are using wastewater-based epidemiology to monitor Saskatoon’s wastewater for SARS-CoV-2 (the virus causing COVID-19), providing early warning of infection outbreaks.
Most people with COVID-19 start shedding SARS-CoV-2 within 24 hours of being infected through their feces. This “viral signal” detected in wastewater helps provide population-level estimates of the rate of infection in a city, indicating whether the number of infected people in Saskatoon is increasing, decreasing or staying the same. This signal is a leading indicator of impending surges in number of active cases by 7 to 10 days following sample collection. To learn more, please see below.
Understanding the data
- The following figures provide the most recent data for the City of Saskatoon (July 20, 2020 to May 5, 2021).
- When interpreting these data, increases in the viral signal in the wastewater are roughly indicative of increases in new positive cases in the following 7-10 days, and decreases are roughly indicative of anticipated decreases in new positive cases.
- It is important to note that the magnitudes of these changes are not always proportional, i.e., a four-fold increase in the viral signal does not always correspond to a four-fold increase in case numbers; it should rather be seen as a gauge for the direction of change.
- This variant tracking data should be seen merely as an indicator of trends that need to be verified using sequencing technology through the Public Health Agency of Canada.
- While detecting trends through wastewater surveillance can help inform modelling of COVID-19 spread, residents should rely on provincial COVID-19 updates as their primary source of information and follow all provincial COVID-19 prevention health orders and guidelines.
This graph shows the five-day moving average of new COVID-19 cases in Saskatoon, SK (blue line; source Saskatchewan's COVID-19 dashboard) and wastewater surveillance data (orange bars), which is a normalized virus load per 100 millilitres of wastewater. These results were generated using an RT-qPCR test for the viral nucleocapsid (N2) gene and adjusted for the extraction efficiency of viral RNA.
The graph shows the percentage of the D3L mutation in the viral nucleocapsid gene found in wastewater that distinguishes the B.1.1.7 (UK) variant of concern (VOC) from wild-type SARS-CoV-2 and other VOCs. These results were generated using an RT-qPCR test. Results will be verified using sequencing technology through PHAC.
Status and Trends Through May 5, 2021:
- From April 28 – May 5, a 25% increase in viral RNA load in Saskatoon’s wastewater was observed compared to the previous week (up to April 27).
- This increase in viral RNA load is predictive of a moderate increase in the number of new cases in Saskatoon in the upcoming week(s).
- Currently, 53% of the viral RNA load in wastewater is contributed by the B.1.1.7 (UK) variant of concern, which corresponds to an 18% decrease compared to the previous week (up to April 27).
- The presence of P.1 (Brazil) was confirmed in the wastewater, while B.1.351 (South African) was not present. Tests for variants were done using RT-qPCR.
- All data has been shared with Saskatchewan health authorities.
NOTE: One value from the previous reporting period (April 27) was removed due to a labelling issue.
Data will be updated on the site every Monday afternoon.
COVID-19 & Wastewater
Join us in our free online academic forum focused on the topic of COVID-19 and our wastewater systems.
Dr. Jay Famiglietti, Global Institute for Water Security
Dr. Marcus Brinkmann, University of Saskatchewan,
Bernadette Conant, CEO of Canadian Water Network
Measuring Virus Indicators in Wastewater as an Early Warning of COVID-19 Outbreaks
Most people with COVID-19 start shedding SARS-CoV-2 through their stool within 24 hours of being infected. This “viral signal” detected in wastewater helps provide population-level estimates of the rate of infection in a municipality, indicating whether the number of infected people in Saskatoon is increasing, decreasing or staying the same. Even a few days of early warning in communities can be critical to the success of pandemic preparedness measures, especially for rapidly evolving variants.
The viral wastewater signal is a leading indicator of impending surges in numbers of active cases that precede increases in new positive cases by seven to 10 days. By gathering this information which in effect surveys all of the individuals connected to the wastewater collection system, the team and its partners are able to warn of upcoming increases in positive cases (see news releases below).
This information on the level of the coronavirus genetic material (known as RNA) complements testing performed on individuals (swab testing) that is the centerpiece of COVID-19 surveillance strategies globally.
Swab tests are limited by the fact that COVID-19 symptoms might not appear for as many as five days after infection. These tests do not capture cases of people who are already infected but do not yet show symptoms (pre-symptomatic), or those who show no symptoms at all (asymptomatic), or only very mild ones (oligosymptomatic). As well, not everyone with COVID-19 is tested, and obtaining results can take time.
The research team has also begun to screen Saskatoon’s wastewater for the B.1.1.7 variant of concern (VOC) first detected in the U.K. in September of 2020. Additional variants will be added to the panel as the situation evolves.
This variant tracking data should be seen merely as an indicator of trends which need to be verified using sequencing technology through the Public Health Agency of Canada. Because individuals are at varying stages of infection when shedding the virus, the variant levels detected in sewage are not necessarily directly comparable to the proportion of variant cases found in individual swab samples confirmed through provincial genetic sequencing efforts.
USask is now designated as the Prairie Node of PHACs Canada-wide WBE efforts and has expanded to testing wastewater from other communities in Saskatchewan, including five First Nations in collaboration with the Indigenous Technical Services Cooperative. The team has also successfully participated in an interlab comparison study coordinated by the Canadian Water Network.
Some guidelines for interpreting wastewater data are available from US CDC here.
Researchers and Funding
USask researchers Prof. John P. Giesy (Toxicology Centre and Western College of Veterinary Medicine), Kerry McPhedran (College of Engineering), and Markus Brinkmann (School of Environment and Sustainability, Global Institute for Water Security, and Toxicology Centre), in partnership with the City of Saskatoon and the Saskatchewan Health Authority, have turned to wastewater-based epidemiology (WBE) to monitor Saskatoon's wastewater for SARS-CoV-2, the virus causing COVID-19. The team also includes toxicologist Paul Jones, program manager Dr. Yuwei Xie, engineering PhD student Mohsen Asadi, and Toxicology Centre research associates Dr. Femi Oloye and Jenna Cantin.
This research has initially been funded through the Global Water Futures (GWF) program and has received dedicated funding support from the Public Health Agency of Canada in February. The team has successfully participated in an interlab comparison study coordinated by the Canadian Water Network. The team is grateful for the continued in-kind support through the City of Saskatoon, particularly staff at the City's wastewater treatment plant who provide wastewater samples.
Related USask News Releases
USask partners with Indigenous communities and City of Saskatoon on COVID-19 wastewater study funded by the Public Health Agency of Canada
(USask Research Profile and Impact, Feb 22, 2021)
Imminent surge in new COVID-19 cases in Saskatoon: USask wastewater data
(USask Research Profile and Impact, November 19, 2020)
COVID-19 levels in Saskatoon’s wastewater point to upcoming increase in cases
(USask Research Profile and Impact, October 30, 2020)
For more information, contact:
Victoria Dinh , USask Media Relations
Frequently Asked Questions
In the best case, a vaccinated person would be protected and not get infected with the virus in the first place, thereby preventing any shedding altogether. But data from Israel show that in the relatively rare case that vaccinated individuals contract COVID-19, the cases are usually mild and go alongside a reduction in shedding of the virus, which leads to a reduced infectiousness.
We provide weekly reports to the City of Saskatoon, the Saskatchewan Health Authority, and as well as the Public Health Agency of Canada.
Data from other jurisdictions show that fluctuations in the wastewater collection and treatment system, e.g., influx of water and road salts during snowmelt, can have a considerable impact on the viral signal in wastewater. In Saskatoon, domestic sewers and storm sewers are separate, and average daily flows, water temperatures, dissolved and particulate matter, as well as pH, are remarkably stable throughout the year. All of these factors contribute to the exceptionally high predictive value of wastewater-based surveillance in Saskatoon.
It has been proposed that individual stool samples could be used to test whether a patient tests positive for SARS-CoV-2. However, some studies indicate that not all patients will consistently shed the virus through their feces. Thus, nasopharyngeal swab testing is still considered the gold standard for individual patient testing. Thus, while wastewater data shows the trend of overall infected cases at the municipal level, it is not a diagnosis tool for individuals. Anyone who thinks he or she might have COVID or who has been exposed to someone with COVID should follow Saskatchewan Health Authority instructions and get a swab test.
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