Ontario sewage tests suggest COVID-19 may have plateaued but levels are still high, experts say

Results from facilities testing sewage for COVID-19 across Ontario suggest infection rates may have plateaued, but levels of the omicron variant appear to remain high, experts say.

Andrea Kirkwood, an associate professor of life sciences at Ontario Tech University who is one of several researchers involved in the sewage COVID-19 monitoring project, said earlier this month that all of the sites they are monitoring “are up very sharply. “

Levels later fell from the peak, but researchers are still finding higher virus signaling in the Omicron variant compared to earlier variants, she said.

“But now it’s plateaued,” said Kirkwood, whose team monitors 11 wastewater sites including the Durham region and Simcoe-Muskoka.

Ever since the omicron surge overwhelmed available PCR tests in Ontario and other provinces, eyes have turned to sewage monitoring to get a relative sense of what’s happening with coronavirus infections in an area.

Even before an infected person shows COVID symptoms, they shed parts of the SARS-CoV-2 virus that causes the disease in their feces. This genetic material in the form of RNA can be detected and monitored in wastewater.

It’s not the kind of measure that accurately reflects anything like a case count, but it can help understand disease progression in a community when PCR testing isn’t available.

Now there are some signs that Omicron’s precipitous rise has at least halted, making Kirkwood and other researchers “cautiously optimistic.”

Optimistic with caveats

Robert Delatolla, an associate professor of civil engineering at the University of Ottawa who is co-leading research on wastewater testing for sites like Ottawa and Hamilton, said while the wastewater signal plateaus, it stagnates at “an elevated level.”

“We’re not the tallest signal we’ve ever seen, [but] There’s still a significant proportion of people who lose a viral load,” he said.

CLOCK | Why wastewater data could soon be more important than COVID-19 case numbers:

Why wastewater data could soon be more important than COVID-19 case numbers

Tyson Graber, co-lead of Ottawa’s COVID-19 sewage project, says sewage data could close the gap in official case counts as the Omicron variant outperforms health officials’ ability to test and report cases. 0:53

Lawrence Goodridge, a professor of food microbiology at the University of Guelph who also led the wastewater testing project at the school, agreed that the wastewater signal is “flattening out across the province”.

“However, I advise caution as most of the children have gone back to school this week. So I think some of these kids will get infected and therefore the sewage signal will go up again. So we’ll probably have to see it in a week or two.”

Not up, but no guarantee down

Claire Oswald, an associate professor of geography and environmental studies at Ryerson University who also heads a sewage monitoring network, said her research showed that the sewage signal in her sewage samples rose “quite quickly” in mid-December compared to earlier waves.

But her most recent data, she said, now points to a plateau.

Her team has been monitoring the Humber Wastewater Treatment Plant, which serves over 700,000 people in west Toronto.

“Personally, it’s too early for me to be confident that things will go back down. Effluent monitoring data varies widely,” she said.

“The more data we have, the more confident we will be about whether or not we start going back down. But I can definitely say it’s not on the way up anymore.”

CLOCK | How Wastewater Helps Monitor COVID-19:

How does wastewater help monitor COVID-19?

Ottawa has tested its sewage to better understand how much coronavirus is in the city’s sewage. The project’s co-leader explains how it helps with COVID-19 surveillance. 4:19

Other regions have reported similar results. at Waterloo, Tests show the Omicron variant COVID-19 has pushed infection numbers more than tenfold than ever before, but there are early signs that infections are beginning to weaken there too.

On Thursday, the Government of Ontario announced iShe would begin easing public health restrictions at the end of the month and plans to lift most of the remaining measures by mid-March.

This decision was based on data showing admissions to hospitals and intensive care units have slowed. Also, Public Health Ontario recorded a 15.9 percent positivity rate for COVID-19 from 42,907 PCR test samples, the lowest rate recorded in Ontario since Dec. 21.

dr Kieran Moore, Ontario’s chief medical officer of health, said positivity rates appear to be leveling off between 20 and 25 percent after climbing into the high 30s earlier this month.

CLOCK | A look inside Ottawa’s sewage treatment facility, where COVID-19 samples are collected:

A look inside Ottawa’s sewage treatment facility, where COVID-19 samples are collected

U of O researcher Robert Delatolla explains how people with COVID-19 shed the virus into city sewage. 0:36

PCR tests restricted

Of course, there are limits to what the PCR tests can show, as the criteria were narrowed down significantly in early January, including those in hospitals and those at high risk. The results may significantly underestimate the true number of infected people in the province.

Therefore some experts have said sewage monitoring could be a much more accurate indicator of COVID-19 rates.

“Now that the clinical data is less reliable, people are more interested in it [wastewater surveillance]’ said Oswald.

However, Oswald said the PCR tests and other provincial data just released “are similar to some of the sewage monitoring data that I’ve seen,” giving a stronger indication that the trends could be real.

CLOCK | Sewage samples indicate where COVID-19 cases are located:

Sewage samples indicate where COVID-19 cases are located

Sewage samples from sewage are used to determine the presence of COVID-19 in communities and could provide advance warning of where a second wave is looming. 2:03

‘Fine-tune the technique’

The wastewater monitoring initiative is sampling at over 170 sites covering more than 75 percent of Ontario’s population across all 34 public health units, Gary Wheeler, a spokesman for the Ontario Department of Environment, Conservation and Parks, said in an email to CBC News.

Samples are currently being collected from 117 municipal sites, including sewage treatment plants, pumping stations and lagoons. Samples will also be taken from 57 upstream high-risk locations: correctional facilities, hospitals, nursing homes, retirement homes, emergency shelters, university campuses and neighborhood sewers, Wheeler wrote.

“We are able to cover a good portion of the province’s population. And we’ve had the last year to really refine the technique,” Kirkwood said.

“We’ve been able to improve the technique to the point that we’re very confident in what the trends are showing us.”


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