COVID-19 wastewater monitoring dashboard: Technical notes

This dashboard provides data about the levels of COVID-19 and variants found in the wastewater (sewage) of different communities across Canada. This information can help assess 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 continue to improve methods for detecting and measuring COVID-19 in wastewater. 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. The results shown on this page were obtained by PCR testing and genomic sequencing.

Scientists use genomic sequencing to decipher the different genetic fragments of the virus found in the wastewater samples. Once the sequencing reaction is complete, they analyze the sequenced pieces using special software. These programs provide information on the variants and the relative amount of each variant detected in a wastewater sample.

We’ve compared wastewater signal trends 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 wastewater viral load testing as a 7-day rolling average. This is 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 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 more context to COVID-19 signals, we’ve developed a signal level metric to compare recent COVID-19 levels to historical levels. For each sampling location, we use viral loads from all samples collected since December 1, 2021, to:

Values below the 25th percentile are classified as low, values above the 75th percentile are classified as high, and the rest are classified as medium.

At least 10 samples are needed to calculate the trend and level metrics. For the signal level metric, sites are marked as new if:

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.

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.
2023-12-15 Surveillance data for Bathurst, Campbellton, Fredericton, Miramichi and Moncton has been replaced by data originating from Vitalité Health Network in New Brunswick. Historical data analyzed by the National Microbiology Laboratory is still available for download.
2023-12-15 Historical data for Edmundston and Saint John have been updated with a new quantification method to more accurately reflect the laboratory process.
2024-02-23 Wastewater activity updates for the following Saskatchewan sites are on hold due to a pause in samples sent to PHAC:
  • Canora
  • Pasqua FN
  • Prince Albert
  • Watrous

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