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Latest wastewater surveillance data shows slight decrease in presence of Omicron

Unpredictability of virus means it's too early to tell if it indicates Omicron has plateaued in Waterloo region, said professor leading study

Tracking the rise in cases of the Omicron variant hasn’t been as clear cut since the province reduced access to PCR testing to prioritize vulnerable populations.

It means case counts issued daily by public health are no longer reflective of the complete picture in terms of how many people are infected with the virus.

But a complementary approach to monitoring COVID’s impact in the region has been in play for over a year and is providing the public health unit with an effective independent tool to monitor infections in the community.

Over the next few weeks, it’s expected to be particularly useful in tracking the decline of the Omicron wave, said University of Waterloo biology professor Mark Servos in last week’s community update from public health.

The Canada Research Chair in Water Quality Protection is leading local municipal wastewater surveillance for the virus with a team of researchers from the university.

They do it by counting fragments of the virus found in samples collected from wastewater plants in Cambridge, Kitchener and Waterloo. 

Specific variants in the wastewater are tracked by looking for identifying genetic markers.

“Any individual that contributes to the wastewater system, ie. anybody that uses a toilet, is essentially going to get captured in that wastewater signal,” Servos explained during last week’s community update.

That capture is made regardless of whether you’re symptomatic, whether you’ve had a vaccine, or your ability or willingness to be tested, he said.

The first sign Omicron's decline may be on the horizon came with Thursday’s wastewater signal update for Cambridge.

The updated graph on the region’s website shows a slight dip in the seven-day moving average for raw copies of the virus collected at the Galt wastewater treatment plant.

A peak seven-day moving average of 329.51 copies per millilitre of the raw SARS-CoV-2 N-gene signal in samples collected Jan. 6, drops to 266.85 copies per mL on Jan. 8.

Kitchener's wastewater surveillance shows a similar drop, from a seven-day moving average of 664 copies of the gene signal per mL sampled on Jan. 7, to 553 copies per mL sampled on Jan. 8.

Is the apparent plateau an indication the province’s restrictions are having an impact on the spread of the virus?

Servos said it’s hard to say, adding what is clear is that restrictions play a key role in controlling the spread.

Everyone’s actions now are critical to protecting hospital capacity and ensuring we avoid a crisis, he said.

He remains cautious, however, on what the latest signal means in terms of a decline.

“The wastewater starting to plateau is an indication that this wave may be peaking but this virus has been unpredictable,” he told CambridgeToday in an email response. 

“In a few days we should have a good idea about the trends and this will inform and support our Public Health officials.”

The wastewater surveillance tool is updated every Thursday at 1:30 p.m. on the region's website where it's measured against the seven-day moving average in positive case counts.

Up until a few weeks ago, before testing capacity was limited, clinical case reports closely followed the seven day reporting average for the wastewater signal.

That signal has seen a dramatic increase since mid December and "it's very clear Omicron is driving this very incredible increase," Servos said.

Up until a month ago, the Delta variant of the SARS-CoV-2 virus represented over 80 per cent of the signal.

Omicron now represents close to 100 per cent of the COVID signal in the region’s wastewater.

“It is as much as ten times higher than any values that we have reported in the previous waves,” Servos said, adding it supports the conclusion that there is “very widespread community exposure to the virus at this point in time and it’s continuing to increase.”