Results from facilities testing sewage for COVID-19 across Ontario indicate that infection rates may have plateaued, yet levels of the Omicron variant appear to remain high, experts say.
Andrea Kirkwood, an associate professor of biological science at Ontario Tech University who is one of a number of researchers involved in the wastewater COVID-19 surveillance project, said at the beginning of the month, all the sites they were monitoring "spiked really high."
Levels subsequently came down from the peak, but researchers are still detecting a higher virus signal with the Omicron variant compared to previous variants, she said.
"But now it's plateaued," said Kirkwood, whose team monitors 11 wastewater sites, which include Durham Region and Simcoe-Muskoka.
Since the Omicron surge overwhelmed available PCR testing in Ontario and other provinces, eyes have turned to wastewater monitoring for a relative sense of what's happening with coronavirus infections in an area.
Even before an infected person shows COVID symptoms, they shed bits of the SARS-CoV-2 virus, which causes the disease, in their feces. That genetic material in the form of RNA can be detected and monitored in wastewater.
It's not the kind of measure that gives something exact like a case count, but it can help understand the trajectory of disease in a community when PCR testing isn't available.
Now, there are a few signs that Omicron's steep climb has at least paused, leaving Kirkwood and other researchers "cautiously optimistic."
Optimistic, with caveats
Robert Delatolla, an associate professor of civil engineering at the University of Ottawa, who co-leads the research into wastewater testing for sites that include Ottawa and Hamilton, said while the wastewater signal is plateauing, it's plateauing at "an elevated level."
"We're not the highest signal we've ever seen, [but] there is still a significant proportion of people that are shedding a viral load," he said.
Lawrence Goodridge, a professor of food microbiology at the University of Guelph, who has also been leading the wastewater testing project at the school, agreed the wastewater signal is "flattening across the province."
"However, I urge caution with this because most kids went back to school this week. So I think some of those kids will get infected and therefore the wastewater signal is going to go back up. So we'll have to see in probably a week or two"
Not up, but no guarantee of down
Claire Oswald, a Ryerson University associate professor in geography and environmental studies, who is also leading a wastewater surveillance monitoring network, said their research indicated that in mid-December, the wastewater signal in their sewage samples went up "quite rapidly" compared to previous waves.
But their most recent data, she said, now indicate a plateau.
Her team has been monitoring the Humber Wastewater Treatment Plant, which serves over 700,000 people in the west side of Toronto.
"Personally, it's too early for me to feel confident that it's going to go back down.There's a lot of variability in wastewater surveillance data," she said.
"The more data we have, the more confident we're going to feel about whether or not we're starting to head back down. But I definitely can say it's not heading back up anymore."
Other regions have reported similar results. In Waterloo, testing shows the Omicron variant of COVID-19 has pushed infection levels to more than 10 times higher than ever before but there are early indications that infections may be starting to level off there too.
On Thursday, the Ontario government announced it would begin easing public health restrictions at the end of the month, and plan to lift most remaining measures by mid-March.
That decision was based on data that show new admissions to hospital and ICUs have begun to slow. As well, Public Health Ontario logged a 15.9 per cent positivity rate of COVID-19 on 42,907 PCR test samples, the lowest rate recorded in Ontario since Dec. 21.
Dr. Kieran Moore, Ontario's chief medical officer of healh, said that positivity rates appear to be flattening between 20 and 25 per cent, after climbing into the high 30s earlier this month.
PCR testing restricted
There are, of course, limits to what the PCR tests can show since criteria was significantly restricted in early January, including those in hospitals and high-risk individuals. Results may significantly underplay the actual number of people in the province who are infected.
That's why some experts have said wastewater surveillance may be a much more accurate indicator of COVID-19 rates.
"Now that the clinical data is less reliable, people are more interested in [wastewater surveillance],"Oswald said.".And I think there's potential for it to give us a clearer picture of what's going on."
But Oswald said the PCR tests and other provincial data just released "do look similar to some of the wastewater surveillance data that I've seen," giving a stronger suggestion the trends may be real.
'Fine tune the technique'
The wastewater surveillance initiative is sampling at over 170 locations covering more than 75 per cent of Ontario's population across all 34 public health units, said Gary Wheeler, a spokesperson for the Ontario Ministry of the Environment, Conservation and Parks, in an email to CBC News.
Currently, samples are collected from 117 community sites, which include wastewater treatment plants, pumping stations and lagoons. Samples are also taken from 57 upstream high-risk congregate locations: correctional facilities, hospitals, long-term care homes, retirement homes, shelters, university campuses and neighbourhood sewersheds, Wheeler wrote.
"We're able to capture a good chunk of the population of the province. And we had the last year to really fine tune the technique," Kirkwood said.
"We were able to to really correct to improve the technique to the point that we're very confident in what the trends are showing us."
ABOUT THE AUTHOR
Mark Gollom is a Toronto-based reporter with CBC News. He covers Canadian and U.S. politics and current affairs.
With files from Emily Chung, Jackie Sharkey
Credit belongs to : www.cbc.ca