Ontario sewage tests indicate slow decline of COVID-19 infection rates

Results from over 80 facilities testing sewage for COVID-19 across Ontarioreveal that infection rates in the provincehave slowly declined following a peak at the beginning of the month.

But scientists, while expressingcautious optimism, say the reopening of schools and loosening of restrictions could send those rates back up.

"Of course it'sgood news, but we just we shouldn't get ahead of ourselves," Dr. Peter Juni,scientific director of Ontario's COVID-19 Science Advisory Table, who is involved in the wastewater surveillance project, said Friday night.

"It's really decreasing slowly which makes me cautiously optimistic. But we should be careful not to undo the progress we're making right now."

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 showsCOVIDsymptoms, 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.

While the wastewater data is not as exact as case counts, it can help understand the trajectory of disease in a community when PCR testing isn't available.

The results from 84 wastewater treatment plants in 33 public health unitshavebeen published on Ontario'sCOVID-19 Science Advisory Table's onlinedashboard. Thedata shows a peak of virus concentration in wastewater around Jan. 4, then falling by about a quarter by Jan. 17.

Junicautioned that the decrease in the infection rate is not a natural wavebut caused by "changing our behaviour" due to publichealth measures that came inafter New Years.

"This is notthe steep increaseand then decrease as we saw it in South Africa, for example. It goesmuch slower right now because this is us flattening the wave."

"It means we need to be slow with reopening and fast with vaccinating," he said.

Levels still high

Although the provincial data shows an overallslow decline, some researchers have recorded a plateau of infection ratesthat remain at a high level.

Andrea Kirkwood, an associate professor of biological science at Ontario Tech University who is one of a number of researchers involved in thewastewater COVID-19surveillanceproject, said at the beginning of the month, all the sites they were monitoring "spiked really high."

Levels subsequently came down from the peak, butresearchers arestill detecting a higher virus signal with the Omicron variant compared to previous variants, she said.

"But now it's plateaued," said Kirkwood, whose teammonitors 11 wastewatersites, which include Durham Regionand Simcoe-Muskoka.

RobertDelatolla,an associateprofessor 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.

WATCH | Why wastewater data might soon be more important than COVID-19 case counts:

Why wastewater data might soon be more important than COVID-19 case counts

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Tyson Graber, co-lead investigator on the COVID-19 wastewater project in Ottawa, says wastewater data may fill the gap in official case counts as the Omicron variant outpaces the ability of public health officials to test and report cases.

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, Iurge 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 goback up. So we'll have to see in probablya week or two."

Not up, but no guarantee of down

Claire Oswald,a Ryerson University associateprofessor in geography and environmental studies, who is also leading awastewater surveillance monitoring network, said their research indicated that inmid-December, the wastewater signalin theirsewage samples wentup "quite rapidly" compared to previous waves.

But their most recent data, she said, nowindicate a plateau.

Her team has been monitoring the HumberWastewater 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."

WATCH | How does wastewater help with surveillance of COVID-19:

How does wastewater help with surveillance of COVID-19?

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Ottawa has been testing its wastewater to get a better understanding of how much of the coronavirus is in the city's sewage. The project's co-lead investigator explains how it helps with surveilling COVID-19.

Other regions have reported similar results. In Waterloo, testing showsthe 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 publichealth restrictions at the end of the month, andplan to lift most remaining measures by mid-March.

That decision was based on data that shownew admissions to hospital and ICUs havebegun 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 health, saidthat positivity rates appear to be flattening between 20 and 25 per cent, after climbing into the high30s earlier this month.

WATCH |A look inside Ottawa's wastewater facility where COVID-19 samples are collected:

A look inside Ottawa's wastewater facility where COVID-19 samples are collected

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U of O researcher Robert Delatolla explains how people with COVID-19 shed the virus into the city's wastewater.

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 andhigh-risk individuals. Results may significantly underplay theactual number of people in theprovince who areinfected.

That's whysome experts have said wastewater surveillance may be amuch more accurate indicator of COVID-19 rates.

"Now that the clinical data is less reliable,peopleare 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 thePCR testsand 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.

WATCH |Wastewater samples point to where COVID-19 cases are:

Wastewater samples point to where COVID-19 cases are

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Wastewater samples from sewage are being used to determine the existence of COVID-19 in communities and could give advance warning of where a second wave is taking shape.

'Fine tune the technique'

The wastewater surveillance initiative is sampling at over 170 locations covering more than 75 per centof Ontario's population across all 34 public health units, said Gary Wheeler, a spokesperson for the OntarioMinistry 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 campusesand neighbourhood sewersheds, Wheelerwrote.

"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 toreally improve the technique to the point that we're very confident in what the trends are showing us."