Viral load down in Saskatoon, Prince Albert and North Battleford wastewater

Omicron BA.2 made up the biggest proportion of COVID-19 viral load in the wastewater of three cities in recent testing.

Omicron BA.2 makes up biggest proportion of viral load in wastewater of all three cities

Researchers take samples from water treatment plants across the province to see whether evidence of COVID-19 is increasing or decreasing. (Richard Agecoutay/CBC)

Researchers at the University of Saskatchewan have published the latest wastewater data, revealing a drop of viral load in the wastewater of several Saskatchewan cities.

Scientists from the university's Global Institute for Water Security continue to monitor wastewater from Saskatoon, North Battleford and Prince Albert for the viral RNA load of SARS-CoV-2, the virus that causes COVID-19.

Findings in Saskatoon from the latest reporting period up to March 25 showed a 74.4 per cent week-over-week decrease in viral RNA (ribonucleic acid) load in the city's wastewater, according to an email from University of Saskatchewan toxicologist John Giesy.

The drop in viral RNA load is indicating a potential decrease in SARS-CoV-2 infections in Saskatoon, which in a partially vaccinated population "may or may not be reflected by new case numbers in upcoming weeks," Giesy's email said.

The wastewater samples can help predict a rise or fall in positive cases seven to 10 days from the time they are taken, according to the Global Institute for Water Security.

Most people start shedding COVID-19 through their feces within 24 hours of being infected, the institute says on its website.

"We saw drops that were pretty substantial across all three major cities," said Markus Brinkmann, assistant professor at the University of Saskatchewan's school of environment and sustainability, member of the Global Institute for Water Security.

"It's a pretty hopeful kind of change of results, because last week it looked very different."

During the previous reporting period, evidence of COVID-19 in Saskatoon's wastewater had increased by 66 per cent compared with the previous week. 

This week's decrease might be an encouraging sign, but it cannot be called a downward trend yet, said Brinkmann.

"We would like to wait one more week or so to really call it a trend," he said.

"Across the entire Omicron wave it has been at pretty high levels consistently, and it did meander around quite a bit, but still staying at relatively high levels."

Viral load also down in Prince Albert and North Battleford

For North Battleford's wastewater, scientists noticed a drop of 56 per cent in viral RNA in the reporting period up to March 25 compared to the weekly average of the previous reporting span.

Recent wastewater statistics also look promising in Prince Albert. In his email, Giesy said viral RNA load in the city's wastewater has declined by almost 92 per cent, based on averages of three individual daily measurements in the reporting period up to last Friday.

Researchers are also monitoring wastewater for the type of SARS-CoV-2 RNA load.

In all three cities, the Omicron subvariant BA.2 was taking up the largest proportion, with almost 79 per cent in Saskatoon, 81.1 per cent in Prince Albert, and 68.6 per cent in North Battleford.

The other viral load detected in the cities' wastewater was Omicron BA.1, while other lineages took up 0 per cent.

BA.2 has replaced BA.1 in Saskatchewan and across Canada, according to Brinkmann.

"Normally what you see is that the more transmissible variants of concern will at some point sooner or later displace the less transmissible ones," said Brinkmann.

"That's certainly the case with B.A.2, which is the sub-lineage of Omicron and seems to be more transmissible than BA.1, which was the original Omicron strain that made its way across the globe."

The University of Regina had not released its most recent data for the Queen City by the time this article was published.