Ottawa COVID-19 wastewater surveillance

Wastewater plots last updated: 15 November, 2022, 09:57:41

Wastewater samples collected up to: 09 November, 2022

Reported date up to: 15 November, 2022

The website is updated Monday to Friday at approximately 5 p.m. Updates can be delayed if measurements do not pass quality assurance and quality control checks.

Samples that are collected from Monday to Thursday are processed the day after collection. The website and plots are updated the day after processing. Samples that are collected from Friday to Sunday are processed on Monday and thus are posted to the website on Tuesday at 5 p.m.

People with COVID-19 shed the causative SARS-CoV-2 virus in their stool, regardless of whether they have symptoms, receive a COVID-19 test or ever are diagnosed. Thus, in contrast to assessing community COVID-19 levels by measuring the number of active cases, which may miss asymptomatic infections as well as be subject to limited test availability, wastewater surveillance consistently captures most of the population with COVID-19 given that everyone goes to the washroom. In addition to serving as a valuable confirmatory data source for COVID-19 levels, wastewater can also serve as early indicator for possible outbreaks, as described below.


For mobile users, dragging the plot while in landscape mode will allow you to view current data. Using the display options at the top allows you to modify the view by zooming in and out of the plot.

Data last reported 2022-11-10. Click here for more details on wastewater data reporting.

*Rolling mean viral signal omits dates (coloured in blue) flagged by wastewater researchers with potential data concerns. Data is currently being studied for effects of snow melt and other diluting factors on RNA signal.


The next plot illustrates the 7-day rolling mean in daily COVID-19 wastewater viral signal. This number is the average of a week’s readings; today’s reading with the previous six days. Also on the graph are various comparators (e.g. reported daily COVID-19 cases, hospitalization count), which can be individually selected by toggling the menu on the right.



Wastewater Projections

Preliminary projections forecasting viral signal are shown below. Projections forecast normalized viral copies per copy based on observed signal data. Caution is encouraged when interpreting results. Methods have not been peer-reviewed, and validation is ongoing.


Current growth estimates for the amount of virus in wastewater

measure estimate
Expected change in viral amount Unsure
Rate of growth 0.0046 (-0.06 – 0.076)
Doubling/halving time (days) 150 (9.1 – -12)

Variants of Concern

The figure below illustrates the proportion of variants of concern (VOC) found in Ottawa wastewater.


Overall viral signal

  • Standard curves R 2 ≥ 0.95.

  • Primer efficiency between 90%-130%.

  • No template controls are negative.


Influenza virus

Samples are screened for influenza A virus (IAV) once a week during the summer period (April to September). Samples are screened daily for IAV and influenza B virus (IBV) during the winter period (October to March). The website and plots are updated the day after processing.

The next plot illustrate the 7-day rolling mean in daily IAV wastewater viral signal. This number is the average of a week’s daily readings.

Respiratory Syncytial Virus Infection (RSV)

Samples are screened daily for respiratory syncytial virus (RSV) during the winter period (October to March). This test does not differentiate between RSV A and RSV B strains. The website and plots are updated the day after processing.

The next plots illustrate the 7-day rolling mean in daily RSV wastewater viral signal. This number is the average of a week’s daily readings. RSV is not a reportable disease, meaning that it does not fall under the list of diseases of public health significance in Ontario as designated by the Minister of Health\(^1\). Nevertheless, RSV has been identified as a disease that could benefit from wastewater-based surveillance given its contribution to seasonal emergency department visits and hospitalizations among young children and to outbreaks in healthcare institutions such as long-term care homes. Visit Respiratory Virus Detections in Canada for more information on RSV surveillance.

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Interpretation cautions

The accuracy and reliability of SARS-CoV-2, influenza and RSV wastewater testing is improving as scientists understand the role of factors such as differences in sewage systems and laboratory protocols. Nonetheless, we recommend caution when interpreting daily or less then 3-day variation in the viral signal while evaluation of the methodology in public health surveillance is ongoing. Research is underway to arrive at a more precise estimate of sensitivity. For influenza and RSV, the level of detection is currently unknown as less than a year’s worth of data has been collected, but evaluation is ongoing. Thus, direct comparisons between wastewater signal levels for the 3 viruses is not recommended at this time. COVID-19, influenza and RSV wastewater signal is helpful when interpreted alongside other surveillance measures, taking into consideration the strengths and limitations of each measure. It is most promising as an early indicator\(^2\) of community viral activity and illness and may serve as a warning in advance of increased care-seeking, outbreaks and hospitalizations.

Visit the Ottawa Public Health Respiratory and Enteric Surveillance Report for more information on Ottawa’s public health surveillance of respiratory and enteric viruses.

For more information on wastewater testing in Ottawa, please see the contact page.

Citations:

  1. Health Protection and Promotion Act, R.S.O. 1990, c. H.7. https://www.ontario.ca/laws/statute/90h07?search=diseases+of+public+health+significance.

  2. Mercier, É. et al. Wastewater surveillance of influenza activity: Early detection, surveillance, and subtyping in city and neighbourhood communities (preprint). (2022) doi:10.1101/2022.06.28.22276884.


See the Methods page for more information on how the samples were collected, access to the data, and how the plots were created. The plots are currently for research only and presented to the public for discussion.

You can learn more about wastewater epidemiology and its role in COVID-19 surveillance on Ottawa Public Health’s website.

Definitions

* A 7-day average is generated by averaging the levels from a given day with the six previous days. The average is termed “rolling” as it changes each day.

* For new cases, the reported date is the day the test result is reported by the laboratory. Episode date is the approximate date of COVID-19 infection estimated from information available: the date of symptom onset, test date, or the reported date.

* Percent positivity refers to the percentage of individuals tested for either COVID-19 infection or influenza A infection in a given day that test positive.

* A central question in wastewater epidemiology is determining the proportion of the wastewater that is actually from humans and the proportion that is rain water, snow melt etc. To address this issue, viral copy data is thus normalized using a seasonally stable fecal biomarker; pepper mild mottle virus (PMMoV). See methods for more details.

^ Percent change in 7-day average is calculated by comparing the 7-day average (previous day 1 to 7) with a lagged 7-day average (days 8 to 14).