Testing of wastewater for COVID-19 has begun in Sault

An initiative to test wastewater for signs of COVID-19 positivity has begun in Sault Ste. Marie and in other municipalities across the country.

The testing of wastewater can't nail down case counts, but it can help public health agencies to spot trends, said Dr. Lawrence Goodridge, who heads the wastewater management project for University of Guelph's Ontario Agriculture College.

Thirteen academic and research institutions in Ontario are working together to test the wastewater samples from communities across the province. U of G is responsible for testing in the Niagara region, Sault Ste. Marie, Sudbury, Guelph, as well as Wellington and Dufferin counties, among others.

Goodridge said some public health units signed on to the project soon after it was announced last spring. Ottawa, Chatham-Kent and Windsor were early adopters of the initiative.

“The ones who didn’t see the utility basically said ‘we are doing clinical testing so why do we need wastewater testing?'" said Goodridge. “It has taken a long time to get the public health units collectively to see the utility, however that has changed with Omicron."

What has changed, said Goodridge, is the current lack of testing being done because of a shortage of polymerase chain reaction (PCR) tests available.

"I think why more public health units are starting to look at wastewater surveillance now because there’s no other indicator," he said.

Samples in Sault Ste. Marie are being collected and sent to Health Sciences North Research Institute to completes the PCR test for COVID-19, before the samples are forwarded to U of G for genomic sequencing.

Goodridge said data from wastewater surveillance can be used alongside traditional testing methods.

“This is just one more piece of data you can use. Clinical testing tells you about individuals, while wastewater testing tells you collectively about a community."

Algoma Public Health's wastewater surveillance is still in a very limited and developmental phase, said APH spokesperson Leo Vecchio by email. 

Goodridge said wastewater surveillance samples are most often taken directly in the wastewater treatment plants.

“They are always collecting samples for their own analysis of how the wastewater treatment process is working, so we just get some of those samples, we process it and isolate the RNA and test it by PCR — the same type that is used for clinical testing — and then we also do genomic sequencing," said Goodridge.

The PCR tests show COVID-positivity in the wastewater and results are available almost immediately, said Goodridge, while the genomic sequencing takes about eight to 10 days to complete.

It may take longer, but that genomic sequencing shows much more information than just positivity in the samples, including which strain is present in the wastewater.

“The PCR won’t tell you that, but the sequencing will. We will see different strains or different variants," said Goodridge.

In some municipalities, the wastewater surveillance is being completed in a much more focused way by taking samples from directly from the wastewater lines of long-term care homes, correctional facilities of university residences.

Goodridge's team used this method to test the different residences at U of G separately to avoid having to lockdown the entire campus in case of positive cases being detected from just one building.

“If you sample and find a signal, you can then test the residents and find out who is infected and quarantine them, thereby stopping an outbreak,” he said.