Wastewater data shows shutdown may be improving COVID-19 numbers
B117 variant makes up 60 to 70 per cent of Ottawa's wastewater signal
COVID-19 in Ottawa's wastewater data is on the rise, but it's also showing a possible plateau that might indicate the provincewide shutdown is starting to bring numbers under control.
The amount of COVID-19 in the city's wastewater has been rising rapidly since the beginning of March — except for a short but sudden drop mid last month — but the number may be levelling off.
"We saw [the] wastewater signal increasing at the beginning of March, continuing to increase and really, in the middle of March, increasing to a point where it was getting a little scary," said Tyson Graber, associate research scientist and co-lead investigator on the wastewater monitoring project in Ottawa.
"I'd like to say that we're maybe reaching a plateau now, this week. We'll see in the next few days."
He suspects the recent high numbers are a result of the Easter long weekend, and the plateau might be because of the provincewide shutdown which came into effect on April 3, five days before the province also issued a stay-at-home order.
But he cautioned, with the variants of concern, we can't rely on what we learned from past lockdowns.
"We saw an effect on the wastewater probably about 10 days after lockdown," he said.
"We're in a different pandemic now. This is a different variant of the virus that has very different transmission kinetics, so how it flows through the population is quite a bit faster and so we might expect that lockdowns may not work the same way."
This wastewater data is also telling a different story, one in which the B117 variant, first detected in the U.K., makes up the vast majority of the city's wastewater signal — 60 to 70 per cent of it.
Snowmelt may have affected data
COVID-19 detection in the city's wastewater is an "open science project" as Graber calls it, and one that everyone is watching.
Given the newness of it, those monitoring the data are figuring out some things as they go along — like how snowmelt might affect the data.
Graber said they're "pretty positive" a mid-March thaw caused a suppression of the COVID-19 signal, essentially diluting how much of the virus could be detected in our poop.
While he said they aren't certain why the signal was suppressed, it could be a result of the city's combined sewage storage tunnel brought online late last year and holds back some wastewater during the spring melt so the wastewater treatment plant isn't overwhelmed.
With files from CBC's Hillary Johnstone and The Canadian Press