Ottawa's wastewater suggests COVID-19 levels are plateauing

·4 min read
Ottawa's wastewater suggests COVID-19 levels are plateauing
Ottawa's wastewater suggests COVID-19 levels are plateauing

Scientists measuring the levels of COVID-19 in Ottawa's wastewater say data suggests the recent surge of new infections in the city may be slowing, even plateauing.

Tyson Graber, associate research scientist at CHEO Research Institute and co-lead investigator on the wastewater monitoring project, says the level of SARS-CoV-2 genetic material is levelling off in local samples.

"The good news aspect of the last week or so has been that we may have reached a spike in the wastewater data and also the clinical data, and it seems to be plateauing," said Graber on Thursday. "We would like to see a few more days before we can say for sure."

On Tuesday, Ottawa's medical officer of health Dr. Vera Etches had a similar analysis.

"The wastewater shows that we had a peak I would say about two weeks ago. Beginning in October, we started seeing a steep rise in the level of COVID showing up in the wastewater, and then about two weeks ago that started to come down, and then it's gone back up a bit again," she said.

"The wastewater shows that we're stabilizing perhaps at a higher level. We'll have to keep watching the trend."

While Etches was careful to say the wastewater levels aren't as low as Ottawa Public Health would like them to be, "this idea of COVID being slowed down is there," she said.

Science improving at breakneck speed

When Ottawa first began taking samples of wastewater and measuring fragments of SARS-CoV-2 viral RNA — in other words, genetic material — the city was one of only a handful worldwide doing this research, said Graber.

Now, sampling wastewater has "ballooned," he said, especially as cities like Ottawa showed the data from wastewater correlated to reported cases from nasal swabs. As more scientists get involved, techniques are being fine-tuned in real time.

Mike Crawley/CBC
Mike Crawley/CBC

The City of Ottawa now uses underground plumbing to extract six samples of sediment or sludge each day, four hours apart. The samples are then taken to a University of Ottawa lab and analyzed. It's a far cry from March, when samples were removed from cylindrical tanks, or clarifiers, using buckets and brought to the CHEO lab.

The researchers now use a control which helps filter out results that might be off because of weather.

The CHEO team uses the presence of a harmless virus most of us shed in our stool from peppers, called pepper mild mottle virus, to help standardize the amount of COVID-19 reported in its findings.

"You can imagine that if there's a big rain event in Ottawa that goes in the sewers ... that will dilute any signal that's coming through the wastewater plant," Graber said.

"But we can follow this [pepper virus] in the stool, and so this allows us to normalize or standardize so we can account for changes in the amount of water that's going through the treatment plant on any one day."

Rick Bowmer/Associated Press
Rick Bowmer/Associated Press

Graber is also measuring the amount of SARS-CoV-2 protein in the wastewater, something he said no one else is doing at the moment. As the protein is more stable, there's more of it, adding to the accuracy of the analysis, he said.

Lasting legacy

There's still a lot of "crawling in the dark" when it comes to wastewater testing, Graber said. For example, there's still no consensus on whether it can predict surges ahead of regular testing, and it's not clear how to control for superspreaders who may shed more of the virus in their feces and skew results.

Still, Graber has growing confidence the technique will prove to be a legacy of the pandemic.

"The power in wastewater testing is that we're actually surveying the entire population of Ottawa. That's not hyperbole," he said.

"It was very, very exciting for me, and I think everybody on the team, to see that this is really working as it should, as we expected, but it's also a very powerful and a new tool."

Graber hopes the province will soon look at creating a program to standardize wastewater sampling across Ontario and expand the reach of testing.

In an email to CBC, a spokesperson for the province's Environment Ministry said the government is looking at wastewater testing as a promising indicator to "safeguard" both communities and the economy.

"That's why the ministry is working closely with the Ministry of Health and Public Health Ontario to explore opportunities to further this research," said department spokesperson Gary Wheeler.