Use our map to see wastewater COVID trends in the GTA

With Ontario partway through its first week without mask mandates and a lack of widespread provincial testing, you may be wondering about the COVID-19 spread in your community.

In the absence of any official public database of COVID signals in the GTA’s sewage, the Toronto Star brings you its own COVID wastewater signal map to give you a sense as to whether cases are increasing, decreasing or remaining stable in your area.

The Star’s signal map uses data sourced from each GTA public health unit into one location, showing trends in sewersheds or wastewater catchment areas for each treatment plant across the region.

This week, levels are stable for most treatment plant catchment areas across the GTA, except four in Halton, and one each in Durham and York, where levels are increasing, according to the most up-to-date information from the health units. The Star asked Hamilton Public Health for its wastewater catchment area trends, but the agency did not provide the needed information.

For the Star’s signal map, the color red indicates that COVID cases in the sewershed or wastewater catchment area are rising, yellow means cases are stable (little to no change), and green / blue means the signal is going down.

Check back here every Thursday for the latest trends.

However, looking at Ontario as a whole, the picture is more bleak. New province-wide analysis from the COVID-19 Science Advisory Table shows the Ontario wastewater signal is increasing sharply. The science table’s scientific director, Dr. Peter Jüni, estimates there are between 20,000 and 25,000 daily infections based on the wastewater signal.

“We are now starting to see exponential growth again and what worries me is that it looks as if it will be relatively steep,” said Jüni. “It’s really important for people to take it slow and not get ahead of themselves with increasing their contacts, with going to crowded places and with dropping their masks.”

He added that the virus’s doubling time detected in wastewater is once again less than seven days, last seen during the second half of December 2021.

“The problem you’re seeing here is not BA.2,” Jüni said. “The challenge is the reopening step of March 1 and the resulting increased contact rates now followed by a potential decrease in masking.”

Wastewater surveillance has become the most accurate method for determining daily cases since the province suspended widespread polymerase chain reaction (PCR) testing at the end of last year.

“Prior to the Omicron wave, we had reasonably good testing in the province… that still gave us a good indication of what the peaks and troughs were,” said Eric Arts, Canada Research Chair in Viral Control and an immunology professor at Western University. “Now we don’t have that at all.”

Wastewater surveillance monitors the genetic fingerprint of SARS-CoV-2, the virus that causes COVID, in water carrying fecal matter that we flush down our toilets. The amount of fragments of the virus’s RNA detected in the wastewater water tells scientists whether cases are going up, down or staying stable in a particular wastewater catchment area.

“It has a good home, both in the intestines of people – the colon – and when it’s released from us into the wastewater,” Arts noted.

Robert Delatolla, a professor at the University of Ottawa whose lab tracks the virus in Ottawa wastewater, said the indicator has never been more important, particularly as COVID trends will show up there before they hit hospitals.

“It’s sort of like a smoke alarm for health resources.”


Conversations are opinions of our readers and are subject to the Code of Conduct. The Star does not endorse these opinions.


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