Canadian Wastewater Survey, December 2021 to January 2022
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Released: 2022-02-18
Measuring the COVID-19 virus (SARS-CoV-2) through wastewater analysis
With the emergence of the Omicron variant, Canada finds itself in the midst of another wave of the COVID-19 pandemic, and confirmed cases of COVID-19 have been at an all-time high in most provinces and territories. Since fall 2020, Statistics Canada has partnered with the National Microbiology Laboratory from the Public Health Agency of Canada to develop methods that detect and monitor levels of SARS-CoV-2, the virus that causes COVID-19, in the wastewater of five cities (Metro Vancouver, Edmonton, Toronto, Montréal and Halifax).
In its commitment to keep Canadians informed, Statistics Canada is now releasing a preliminary dataset from the Canadian Wastewater Survey, covering the period from April 1, 2021 to January 31, 2022. Genomic sequencing shows the Omicron variant in Canada was reported towards the end of November 2021. Statistics Canada will continue to update wastewater data on a regular basis, as results become available.
Analysis of wastewater results from the most recent reference period available (December 2021 to January 2022) shows that in Metro Vancouver and Edmonton, wastewater viral loads continued to increase after clinical case counts peaked. For Toronto and Montréal, these two indicators peaked at approximately the same time, but the levels of SARS-CoV-2 in wastewater do not drop off as quickly. In Halifax, wastewater viral load peaked before clinical case counts.
In the absence of reliable confirmed COVID-19 case data when polymerase chain reaction (PCR) testing was limited, these results demonstrate that regular monitoring of the levels of the virus in wastewater can be used in conjunction with other public health metrics (such as hospitalizations, intensive care unit admissions, and test positivity rates) to provide valuable insights into the disease burden on a community. As the science continues to evolve, we will continue to monitor these changes and update wastewater data regularly.
Omicron put a strain on clinical testing, but wastewater data provide another source of timely and consistent data
Soon after Omicron's detection in late November 2021, both clinical (PCR-based) cases and levels of the SARS-CoV-2 virus in wastewater started to increase quite rapidly. Although health region boundaries do not align exactly with the areas served by the wastewater treatment plants, the comparative analysis between wastewater data and confirmed cases shows that the two data sources paint a similar picture of the pattern of infections. However, when the Omicron wave hit Canada in early December 2021, clinical testing capacity soon became overwhelmed in all five cities. Many provinces and territories moved to limit clinical testing (both PCR and rapid antigen), and instead relied on other indicators of disease burden such as hospitalizations, deaths, test positivity rates, and wastewater.
In Edmonton, the Omicron wave began to be reflected in both wastewater viral loads and confirmed clinical cases around December 12, 2021. Restrictions to PCR testing began on December 23, but didn't result in an immediate drop off in case numbers. Clinical cases peaked on January 13, 2022, however, whereas levels in wastewater were still showing an upward trend until January 20, and subsequently began to decline.
Infographic 1
SARS-CoV-2 levels in wastewater and daily COVID-19 cases in Edmonton
According to wastewater results in Toronto, there was not a large difference between the trends in wastewater viral loads and clinical cases. Confirmed cases peaked on December 30, 2021 while the wastewater signal peaked on January 1, 2022, just as restrictions to PCR testing were put in place, and both case numbers and levels in wastewater had begun to decline when further public health restrictions were put in place on January 9. The levels of the virus in wastewater showed a slower decline, but by January 23, 2022, both clinical cases and levels in wastewater had returned to similar levels compared with mid-December 2021.
Infographic 2
SARS-CoV-2 levels in wastewater and daily COVID-19 cases in Toronto
In Montréal, the trends between clinical cases and levels of the virus found in wastewater were also quite similar to start. Both started increasing in early December 2021, after the first detection of the Omicron variant, and peaked around December 29, 2021. Clinical cases, however, show a consistent decline after this date whereas levels of the virus in wastewater remained relatively high. Levels of the virus in wastewater on January 22, 2022 were some of the highest levels seen since the start of the pandemic, but showed a sharp decline the following week.
Infographic 3
SARS-CoV-2 levels in wastewater and daily COVID-19 cases in Montréal
Halifax is another city where levels in wastewater versus clinical cases were trending in the same direction in early December 2021, and both started to increase after the first detection of the Omicron variant. After restrictions were made to PCR testing on December 27, however, the trends started to diverge. Clinical cases peaked on January 3, 2022, and decreased significantly in the weeks following, whereas the wastewater signal is quite variable over the same period.
Infographic 4
SARS-CoV-2 levels in wastewater and daily COVID-19 cases in Halifax
In Metro Vancouver, confirmed cases reached their peak on December 30, 2021 just as PCR testing was reserved for high-risk groups. However, wastewater results show the upward trend continued for at least another week. The subsequent decline might reflect the public health measures put in place on December 23, 2021. Flooding may also have impacted the wastewater results. Typically, wastewater-based surveillance accounts for normal weather events such as rain or snowfall. However, the 2021 Pacific Southwest floods from November 17, 2021 to January 11, 2022 were caused by an atmospheric river that brought heavy rain and a series of floods to parts of southern British Columbia, including Metro Vancouver. The excess storm water may have led to dilution of the wastewater which could have resulted in lower levels of the SARS-CoV-2 virus being detected in the samples collected during this period.
Infographic 5
SARS-CoV-2 levels in wastewater and daily COVID-19 cases in Metro Vancouver
Collaboration with Public Health Agency of Canada allows for surveillance of pandemic trends
Through the partnership with the Public Health Agency of Canada (PHAC), the analysis of wastewater data covering the emergence of the Omicron wave demonstrates that wastewater analysis is an efficient approach that can serve as an important complementary indicator to help augment various public health metrics, and inform of emerging local pandemic trends at the population level.
Other release products
PHAC COVID-19 wastewater results are being released through the National Collaborating Centre for Infectious Disease (NCCID) website. The NCCID specializes in forging connections between those who generate and those who use infectious disease public health knowledge, and is hosted by the University of Manitoba. Working across disciplines, sectors and jurisdictions, they are uniquely situated to facilitate the creation and operation of networks and partnerships.
Note to readers
The Canadian Wastewater Survey (CWS) has been estimating levels of various licit and illicit drugs in the wastewater of five Canadian cities since 2019. Wastewater-based epidemiology is an emerging field that applies analytical techniques to wastewater in order to estimate consumption of substances, exposure to pollutants, and/or levels of pathogens or antimicrobial resistance at the community level.
At the onset of the COVID-19 pandemic in early 2020, it quickly became apparent to the scientific community that, due to the shedding of the virus in human stools, SARS-CoV-2 could be detected and quantified in wastewater. Indeed, individuals infected with SARS-CoV-2, even when asymptomatic, often shed the virus in their stool.
Since fall 2020, Statistics Canada has collaborated with the Public Health Agency of Canada on a wastewater-based epidemiology program to detect and monitor levels of SARS-CoV-2 in the wastewater of the same five Canadian cities as the CWS, representing close to 8.7 million Canadians.
Wastewater analysis can complement other epidemiological indicators on the burden of COVID-19 (such as number of hospitalizations) while being timely, cost effective (one test per community versus many tests) and easy to deploy, especially to remote areas where resources to carry on systematic clinical testing can be limited. It continues to be an important indicator of the course of the pandemic that complements clinical data.
Limitations
Despite the advantages listed above, there are some methodological and analytical limitations to the approach, meaning the results should be interpreted with caution:
- Samples are only collected twice weekly which, while maintaining accuracy regarding overall trends, can limit data interpretation and trend modelling in narrow time frames.
- There are limitations associated with analytical aspects:
- 1) Estimates of viral load are greatly affected by normalization techniques when using different indicators of the levels of fecal content in the wastewater. Data presented here were not normalized as researchers are still debating the best approach.
- 2) Some variability has been observed when different fractions of the same wastewater sample are repeatedly analyzed.
- 3) External factors such as the weather can have important effects. Year-long differences in ambient temperature will affect how stable the virus genomic particles are in wastewater, impacting accuracy during warm months. Snowmelt, flooding, excess rainfall, and drought conditions will contribute to dilution/concentration of viral signal.
Given the nature of these limitations, results between individual cities should not be compared at face value. The results shown in Infographics 1 to 5 of this article are scaled from zero to the highest measured level of SARS-CoV-2 in wastewater in their respective city during the current reference period. The results shown are not normalized to a specific parameter due to the continued challenges with respect to the methodologies.
Products
The Canadian Wastewater Survey data for the period from April 1, 2021 to January 31, 2022 are now available as part of the Monitoring the COVID-19 virus in wastewater through the Canadian Wastewater Survey: preliminary data release dataset.
Contact information
For more information, or to enquire about the concepts, methods or data quality of this release, contact us (toll-free 1-800-263-1136; 514-283-8300; infostats@statcan.gc.ca) or Media Relations (statcan.mediahotline-ligneinfomedias.statcan@statcan.gc.ca).
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