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Our sewage isn’t as healthy as we might like – even by sewage standards.

While far lower than the viral load recorded in January, levels of SARS-CoV-2 detected in wastewater have increased significantly since the mask mandate was lifted earlier this spring, according to data recently released by Metro Vancouver.

On March 10, provincial health officer Dr. Bonnie Henry announced the mask mandate was being lifted.

The decision was being made, Henry explained, due to a drop in rates of transmissions as well as a “consistent decrease” of the virus in wastewater.

Two months later, we thought it would be a good idea to take a quick look at the rates of virus in the wastewater at the Annacis Island treatment and see where the rates were and where they are. But first, a quick explanation of how it’s done.

How it’s done

Three times a week, researchers from the B.C. Centre for Disease Control and UBC examine untreated wastewater, testing what they find to track rates and possible mutations in COVID-19.

“Studies have demonstrated that approximately 50 percent of COVID-19 cases have the virus in their feces,” said Dr. Natalie Prystajecky, program head of environmental microbiology at the BCCDC Public Health Laboratory while speaking to Environmental Science & Engineering Magazine.

By getting separate data from each wastewater treatment plants, the information can be an early indicator of COVID-19 within the community, lead researcher Dr Melissa Glier told the Burnaby Beacon.

“It’s most informative for establishing trends—to see the increasing or if it’s stable or decreasing within the incidence in community cases,” Glier said.

At the beginning of the pandemic, researchers detected SARS-CoV-2 in the city of Amersfoort before any COVID-19 cases had been confirmed in the city.

The data can serve as a tool for health authorities to judge whether the health measures being used are effective. However, the testing can’t offer a definitive account of the number of British Columbians who are infected or contagious, according to a release from Metro Vancouver.

Where we were

In early January, when daily case counts in Fraser Health were roughly in the 1,600 range, researchers found 406,000 billion gene copies of SARS-CoV-2 in one day’s worth of wastewater.

By Valentine’s Day, that figure had plummeted to 53,000 billion copies, a drop of nearly 87 percent. By that point, daily case counts in Fraser Health were in the 500-800 range.

Judging by wastewater reports at Annacis Island, the viral load continued to decrease through early spring, dropping to 29,000 billion copies by March 7, just before Henry moved to ease restrictions.

Through March and April

The viral load stayed low throughout most of March but researchers recorded 57,000 billion copies on April 2 – nearly twice as many as the previous month.

While inconsistent, the figures generally increased through April, reaching 127,000 billion copies by April 23, the highest since the mask mandate was lifted.

The most recent numbers

A May 2 test showed a viral load of 121,000 billion copies.

The most recent test, conducted on May 9, dropped to 84,682 billion copies, a drop of 30 percent from the May 2 test.

Three-day totals

Cumulatively, three tests recorded between May 4 and May 9 found approximately 250,000 billion copies.

That total represents a 20 percent decline compared to three tests recorded between April 27 and May 2.

However, the most recent three-day total represents nearly three times the viral load documented in early March.

Three tests undertaken between March 9 and 14 showed 85,500 billion copies. The viral load increased to approximately 104,500 billion copies in three tests taken between March 16 and 21.

Numbers from the province

There were 742 COVID-19 cases reported in the Fraser Health region from May to May 7, a dip of 14 percent from the previous week. The trend in Fraser Health followed a province-wide decline in both hospital admissions and cases reported.

Across B.C., there were 331 hospital admissions due to COVID-19 between May 1 and May 7. There were 434 admissions between April 24 and 30.