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Omicron not showing up in wastewater like Delta, despite surging cases

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Wastewater testing in London is showing unexpectedly lower levels of virus despite an Omicron surge that drove the local and provincial case counts to new single-day records Wednesday, Western University researchers say.

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Jennifer Bieman

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Dec 29, 2021  •  4 hours ago  •  2 minute read Eric Arts is a professor of microbiology and immunology at Western’s Schulich School of Medicine and Dentistry and the project lead of a Western team analyzing wastewater for the virus that causes COVID-19. Researchers have found the viral loads in wastewater collected from five local sewage treatment plants lower than anticipated despite a record-breaking surge in COVID-19 cases.  (Mike Hensen/The London Free Press) Eric Arts is a professor of microbiology and immunology at Western’s Schulich School of Medicine and Dentistry and the project lead of a Western team analyzing wastewater for the virus that causes COVID-19. Researchers have found the viral loads in wastewater collected from five local sewage treatment plants lower than anticipated despite a record-breaking surge in COVID-19 cases.  (Mike Hensen/The London Free Press)

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Wastewater testing in London is showing unexpectedly lower levels of virus despite an Omicron surge that drove the local and provincial case counts to new single-day records Wednesday, Western University researchers say.

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With Omicron now the dominant strain in the London area and across the province, the Western team has noticed the viral levels in wastewater collected from five local sewage treatment plants are lower than anticipated despite the record-breaking number of reported cases.

“In wastewater, how much quantity we have (of the virus) doesn’t look as high as what we saw with Delta,” said Eric Arts, project lead and professor of microbiology and immunology at Western’s Schulich School of Medicine and Dentistry.

The disconnect requires further study, he said, but it could be that Omicron – while much more contagious than other strains – isn’t making people sick enough to generate large viral loads that end up in sewage.

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“If the virus is less virulent, it is quite possible that less virus is being shed through the intestinal tract and with fecal material into the wastewater supply,” said Arts, who is also the Canada research chair in HIV pathogenesis and viral control.

Ontario’s daily COVID-19 tally reached a record 10,436 new cases Wednesday , days after it surpassed the 10,000 mark for the first time since the pandemic began.

The Middlesex-London Health Unit reported 378 new COVID-19 cases, surpassing the record daily case count of 357 set Christmas Day.

The London-area health unit also announced one additional COVID-19 death, a centenarian woman who didn’t live in a long-term care or retirement home.

With testing capacity strained by the most recent case surge, Arts said the wastewater data is a more accurate indicator of the scale of COVID-19 spread in the community.

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“Wastewater is a really good predictor of what’s to come,” he said Wednesday.

“I put a little more stock in the wastewater data now and going forward, because if gives a better indicator of the (viral) load in the population.”

The wastewater data can capture asymptomatic infections or people with mild symptoms who forgo testing, Arts said.

The Western team began testing wastewater for the virus late last year but expanded the program in early 2021. Western and other research partners are  tracking the virus’s genetic material in wastewater from communities across Ontario, from Windsor to Cornwall and west to Thunder Bay, Arts said.

The team began testing the samples for variants in the fall, Arts said.

The Western team started seeing a rapid switch from the Delta variant to the Omicron variant in Greater Toronto Area wastewater samples starting around Dec. 10, Arts said. A week later, Omicron represented 50 to 60 per cent of the SARS-COV-2 virus the team identified in the wastewater samples.

It took a little longer for Omicron to become the dominant variant in wastewater samples from Windsor and London, which had a high-profile Omicron cluster identified Dec. 6, Arts said.

London’s case surge has set daily records five times in the last week.

The number of COVID-19 patients at London Health Sciences Centre rose to 22 Wednesday, up from 17 the day before. Of those, eight are in intensive care.

The hospital reported 113 COVID-19 cases among staff Wednesday, up from 104 the previous day.

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