What wastewater can tell us about where Omicron is heading

Stool a key tool in helping scientists track COVID-19 trends.

Thestar.com
Jan. 18, 2022
May Warren

There are some early signals that Omicron may have plateaued in Toronto and several other cities in Ontario, found in what residents are flushing down the toilet.

Experts caution that the return to school might change this, and it may only be a temporary response to public health restrictions.

But there is some cautious optimism to be found in fragments of SARS‑CoV‑2, the virus that causes COVID-19, collected from wastewater treatment plants.

“There may be evidence of a potential plateau or even a decline in virus detected at the four watershed sites,” Toronto’s Medical Officer of Health Dr. Eileen de Villa said at a virtual meeting of the city’s Board of Health on Monday. Those sites are: Ashbridges Bay, Highland Creek, Humber and North Toronto.

“That’s very early on and we’re looking to confirm this,” she said, adding they’ll continue to monitor this indicator closely.

Wastewater sampling is being done at all 34 health units in Ontario, covering about 75 per cent of the province, through a collaboration with academic and research institutions, the Ministry of Health and the Ministry of Environment, Conservation and Parks, according to a spokesperson for the latter.

It’s a relatively novel method of COVID surveillance, but with the traditional testing system overwhelmed, and months of data collection under their belts, researchers are providing input to public health units that’s arguably more important now than ever.

Academics at Ryerson University have been working with the city on COVID wastewater, a method of detecting viral surges that has been used in many other countries, as well as by public health units across the province.

When people get COVID they shed viral fragments in their stool that can be detected in sewage at wastewater treatment plants, even if they never got a test or don’t have symptoms.

In past pandemic waves, wastewater signals have served as an early warning that the virus is rising in a community, even before it starts to show up in tests.

Toronto has not made this data public before. But de Villa said they hope to translate work from its pilot program into a format that’s publicly available as part of its COVID dashboard “as early as next week.” She added it doesn’t seem to be currently valuable as an early warning tool, but does show potential to confirm trends from other data sources.

The Toronto trend is in line with what some other Ontario cities are seeing. According to Peel Public Health’s Jan. 14 epidemiological update, the wastewater signals at both the Clarkson and G.E. Booth wastewater treatment plants have begun to plateau, suggesting that the wave is slowing down.

Prior to that, the most recent peak was nine to 13 times higher than the spring 2021 wave.

In Ottawa, it’s too soon to say that COVID in the wastewater is declining, but researchers are “pretty confident that it’s plateaued,” said Robert Delatolla, a professor at the University of Ottawa whose lab collects wastewater samples to share with Ottawa Public Health.

Over the past almost two years of wastewater testing, his team has found levels stop rising when public health restrictions are in place. But the return to in-person learning may cause them to go up again, he said.

Now that the public lab-testing system has collapsed and polymerase chain reaction (PCR) tests for COVID-19 are restricted to people in high-risk settings, wastewater surveillance becomes even more vital.

“I really feel like as a province and even as a country we really have an opportunity now to leverage all the work we’ve done with wastewater and to really provide a guiding light,” Delatolla said.

In Windsor, Mike McKay, executive director of the University of Windsor’s Great Lakes Institute for Environmental Research, said they were seeing a plateau over recent days, but then saw data go up again Monday. But since the southwestern Ontario region was “late to the party” when it came to Omicron, it may be taking longer to drop there.

His team has stepped up sampling in response to the Omicron-induced restrictions on testing.

“We’ve been at this now for the better part of a year and a half,” he said, “so there’s been quite a community built around this. It’s grown to a point where we are quite confident in the data now.” Looking at past waves, the wastewater levels “track well” with cases.

Researchers have always seen the approach as “just another tool that public health can use in the toolbox that’s available to them, well that toolbox is becoming depleted,” he added.

While officials are closely watching hospitalizations, ICU admissions and deaths, (which continue to rise), these are lagging indicators, he noted.

In certain U.S. cities such as Boston, Omicron seems to be on its way down in wastewater, he added, even though it’s too soon to tell exactly what’s happening here.

“The signal is compressed, not long and drawn out like we’ve seen some of the other waves and resurgences of the virus,” McKay added. “So that’s optimistic.”