COVID-19: Wastewater monitoring dashboard:

This dashboard provides trend data about the levels of COVID-19 in the wastewater (sewage) of different communities and settings across Canada. This can reflect the levels of COVID-19 in those communities.

This page has information about how we conduct wastewater testing and the limitations of the data. It also includes definitions for some of the scientific terms used in this dashboard.

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Methodology

Scientists across the country provide wastewater monitoring data through their provincial and territorial networks. To detect SARS-CoV-2 at the community or institutional level, samples are collected at a central collection point, such as a wastewater treatment plant or pumping station. This method only captures the presence of COVID-19 in the community or institution. It can’t be used to identify single cases or households.

Scientists are still learning about how to detect and measure COVID-19 in wastewater. While there are different ways of doing this, the scientific community, including the Public Health Agency of Canada, is working together to build a standard that will help everyone understand, compare and share data about COVID-19 in wastewater.

We’ve compared the trends of wastewater signals when the same sites are tested by both the National Microbiology Laboratory and provincial and territorial networks. We found that the trends are broadly consistent across labs. Differences in the strength of the wastewater signals are mostly due to differences in processing methods.

We present COVID-19 viral load as a 7-day rolling average because high levels on a single day don’t show the broader trend. Our approach helps us to understand the overall trends while giving you better information to make your own health decisions. Generally, we test sites twice weekly. Exceptions are Alberton and Winnipeg which are tested 1 and 5 times per week, respectively.

We monitor the rise and fall of COVID-19 signals using a technique developed by the Ontario Ministry of the Environment, Conservation and Parks as a part of their provincial wastewater monitoring initiative. The wastewater monitoring 7-day average data is broken into segments over time. The daily change in the viral signal is determined for each segment. Rises and falls of the wastewater signal are judged based on their consistency over time.

For more information, please refer to: Quantitative Trend Analysis of SARS-CoV-2 RNA in Municipal Wastewater Exemplified with Sewershed-Specific COVID-19 Clinical Case Counts.

To provide additional context to COVID-19 signals, we have developed a signal level metric to compare recent COVID-19 levels to historical levels. For each sampling location, we use SARS-CoV-2 levels from all samples collected since December 1, 2021, to calculate the 25th and 75th percentiles and establish lower and upper cutoff values. For newly onboarded sites, we use historical data from similar sites to estimate thresholds. Values below the 25th percentile are classified as low, values above the 75th percentile are classified as high, and values between the two thresholds are classified as medium. Sites are marked as ‘New Site’ if the wastewater testing was established after December 1, 2021 and historical data for the complete post-Omicron period does not exist to establish cutoff values.

At least 10 samples are required to calculate the SARS-CoV-2 trend and level metrics. A site is marked as ‘New Site’ if fewer than 10 samples are reported.

Limitations

While wastewater monitoring offers many advantages, it does have some limitations.

The accuracy of the wastewater signal can be affected by various factors, including the composition of wastewater, which varies by community. For example, ground or surface water can make the COVID-19 wastewater signal stronger or weaker. This can be an issue during seasonal snow-melt and large rain events.

The wastewater signal can also be affected by:

We’re working with our partners to identify other issues with wastewater monitoring and developing measures to reduce the effects.

Wastewater monitoring also detects people with or without symptoms. Considering the above limitations, we’re not sure how much virus is shed with each wave. For this reason we don’t recommend comparing wastewater monitoring data from different waves of COVID-19 to estimate the number of cases in a community.

Definitions

To learn more about wastewater monitoring, please refer to Harnessing the power of wastewater testing to detect COVID-19 outbreaks.

Data changes

Date Notes
2023-05-02 We have temporarily removed Saint John from the dashboard, due to possible issues affecting data accuracy. Once these issues have been investigated and resolved, Saint John will once again be included in the dashboard.
2023-05-12 In January 2023, The National Microbiology Laboratory (NML) updated its protocol to include quantification of standard reference samples to improve accuracy. This change affects data points between July 6, 2022 and February 3, 2023. Data points have been retroactively updated to reflect this change. The updated NML wastewater quantification protocol includes a confirmation of standard reference samples’ concentration via digital PCR.
2023-09-08 Saint John, New Brunswick, has been reincluded in the dashboard with data originating from Dr. Georges-L.-Dumont University Laboratory.

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