With access to COVID-19 tests limited, several Ontario cities are using an additional method to track the virus — sampling wastewater from homes and businesses throughout the city.
And a researcher who’s been tracking what gets flushed down the toilet says she’s finding encouraging data.
“We’re hoping we’re at the peak of the Omicron wave, and the wastewater is really going to help us know when we start turning the corner,” said Elizabeth Edwards
The University of Toronto professor has been working with the City of Toronto and the province to collect COVID data through wastewater samples.
Sampling wastewater, or sewage, is a “relatively novel tool” used globally to help track the presence of the virus in a community without clinical testing, Toronto Medical Officer of Health Dr. Eileen de Villa said in the Toronto Board of Health Meeting on Jan. 17.
“This is a method that’s meant to complement traditional COVID-19 surveillance,” De Villa said.
Edwards said the wastewater treatment plants already test the water for other purposes.
“What we’re doing is piggybacking on that effort, getting a sample of the wastewater just before it enters the plant,” she said.
Edwards explained that when someone is infected with the virus, it can be detected in their waste even though it is no longer infectious at that point, allowing them to safely identify its presence in the wastewater.
“The sample contains all the microorganisms in that wastewater, and so we extract that and purify it, and then we can use specific probes to quantify how much of that material actually comes from the SARS-CoV- 2 virus.”
Edwards said this method is efficient because only one wastewater sample is needed to track COVID-19 data among all the people in that area, rather than having to test each person individually. It is also independent from clinical testing.
“There’s not as much testing going on, so you might not get a representative sample,” she said. “So this is where the wastewater becomes a really good, representative, unbiased sample.”
Since December, Edwards said they have seen a rapid increase in the concentration of the virus in wastewater samples, but the last few samples suggest it may be plateauing.
In other regions, such as Peel and Waterloo, cases seem to be plateauing as well, according to Waterloo University Professor Mark Servos.
“In York region, there’s a tendency to start to decline,” he said.
Servos said it is still too early to tell whether it will start to decline soon, but they sample five days a week and should have that data very soon.
Servos said another advantage of wastewater is the ability to detect different variants in its samples, allowing them to track which variants have been most prevalent. He also said the data collected from wastewater samples is more reliable at this time than clinical testing.
This data is an important factor in the decision-making process of the government’s COVID response plan.
York Region Medical Officer of Health Dr. Barry Pakes said the high number of Omicron cases makes it “impossible” to track all cases through clinical testing, the most common approach in Ontario.
“We are using other metrics like wastewater signals, positivity, hospital admissions, and others, as well as modelling, to guide our decision-making,” Pakes said.
De Villa said while this method is not particularly effective in detecting early warning signs of transmission, it is a useful tool that can help the city to track increases or decreases in the concentration of the virus within the community.