What wastewater testing is telling us about COVID-19 in London, Ont.

After a year of testing London's wastewater for COVID-19, engineer Chris DeGroot thought he and his colleagues on a research team from Western University might get a bit of a break over the Christmas holidays. 

But the Omicron variant had other ideas. 

As cases continued to climb to the point where testing every suspected case became impossible — eventually forcing the province to scale back testing eligibility — the use of sewer water suddenly became crucial. 

"With the Omicron surge, wastewater became really the only way to tell what's going on in the community," said DeGroot.

Instead of slowing down testing over Christmas as planned, they ramped it up to ensure health officials had the most up-to-date data as the variant spread. 

"[Wastewater testing] really gained so much more value," said DeGroot. "The test numbers being reported by the health units and the province are no longer representative of the whole population, whereas wastewater testing is."

Since December 2020, DeGroot and the team from Western had been testing London's wastewater three times a week at the city's five treatment plants. Other Canadian cities have been doing similar testing. It works like this: An infected person sheds fragments of the virus in the fecal matter, which winds up at the sewage treatment plant. 

That's where DeGroot and his colleagues gather the samples, spinning them down to a solid pellet where a PCR analysis can detect the virus. From there, the number of copies of the virus per litre of waste water are calculated out and expressed as the viral load.   

With provincial funding in place to support the testing until at least March, the Western team is now continuing their testing regime and posting their data on this website with regular updates. 

Their most recent data suggests London may have passed the peak of the Omicron surge. 

On Jan. 6, the viral load detected in London was about 121 copies of the virus per cubic metre. In the Jan. 13 sample, that number had dropped to 33. DeGroot wants to see more samples to confirm the trend, but he believes the data suggests the presence of COVID-19 in the community is now moving in the right direction. 

The blue line, which spreads the data points over a seven-day average, also suggests a falling viral load.

Wastewater testing happening down the road in Kitchener-Waterloo suggests a similar trend unfolding there. And yesterday the province announced they expect the number of new COVID-19 cases to peak sometime this month.

Of course as we've learned in recent weeks things can change quickly when it comes to COIVD-19, but certainly wastewater testing has proven its utility as a testing tool.