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Individual flights arriving from China at Vancouver International Airport and Toronto Pearson International Airport will have their sewage pumped and tested for COVID-19.DARRYL DYCK/The Canadian Press

Flights landing at Vancouver’s and Toronto’s international airports from China and Hong Kong will have their wastewater removed and tested for COVID-19 starting later this month, a move Ottawa says will help Canada gauge the prevalence of the virus arriving from the region as well as detect new mutations.

A year ago, the Public Health Agency of Canada began partnering with Toronto’s Pearson International Airport and researchers at three Ontario universities to analyze the sewage from all aircraft arriving at the main terminals. That wastewater is still being collected and screened with genomic sequencing to identify the subvariants of Omicron and new strains.

Now, individual planes at Pearson and Vancouver International Airport will have their sewage pumped to allow test results to be broken down by flight as part of twin projects due to start later this month, PHAC said in a statement. Vancouver’s airport, the main flight hub in British Columbia, will also have the sewage from all its other flights collected directly from its terminal and tested, like with Pearson’s year-old system, PHAC added.

The agency did not say how long this “short-term” targeted testing would occur, but, starting Thursday for the next month, passengers on these same flights must obey a new federal rule that requires a negative COVID-19 test before boarding a plane bound for Canada. Australia, Britain, France and the United States have imposed similar testing requirements in response to a surge of COVID-19 cases in China, where the government has moved away from a long-standing zero-COVID policy.

Last week, the World Health Organization urged Chinese officials to regularly share specific and real-time COVID-19 data. The WHO previously has said that Beijing may be struggling to keep a tally of infections, and the U.S. government has attributed its test requirement to a lack of information around variants in China and concern that the surge of new cases could result in new mutations being developed.

On Tuesday, the British Columbia Centre for Disease Control confirmed it had found five cases of the XBB.1.5 subvariant of Omicron, which is believed to have become the most dominant strain of COVID-19 in the United States over the holidays.

Tori Gass, a spokesperson with the Greater Toronto Airports Authority, the non-profit that runs Pearson, said the current testing regime acts as an “early warning system” for these variants and subvariants as well as other infectious diseases that endanger public health, such as monkeypox and polio.

After the first wave of Omicron swamped many of the free public testing regimes across the country and then provincial governments stopped offering this service widely, sampling sewage to find population-level transmission trends became one of the most reliable methods of tracking the spread of COVID-19.

But estimating the prevalence of the virus among passengers at Canada’s busiest airport is very difficult under the current regime at Pearson, according to Lawrence Goodridge, director at the Canadian Research Institute for Food Safety at Guelph University, whose team is helping analyze these samples. That’s because people shed different levels of the virus and the DNA from the COVID-19 strains is often spliced as it mixes in the sewage, Dr. Goodridge said.

“I’ve always made it clear it is not a panacea, it does not replace clinical testing,” he told The Globe and Mail.

The scientific value of the airport sewage testing, Dr. Goodridge said, is to identify dangerous subvariants of Omicron entering Canada, which is being done “from a single sample testing all the planes” from the terminals’ sewage system. (His lab had to shut down over the university’s winter holidays so this week it is still testing samples taken after Christmas for subvariants such as XBB.1.5, he said.)

Targeting individual Chinese flights is less useful, Dr. Goodridge said, because people can leave that country and connect through any number of other airports to enter Canada.

His colleague Robert Delatolla disagrees. Dr. Delatolla, a professor of environmental engineering running a University of Ottawa lab that has been analyzing local sewage for COVID-19 since April, 2020, said testing individual flights could increase the lead time that this “smoke signal” provides for the authorities to prepare for the next variant or subvariant.

“It’s not going to change anything, it’s going to come regardless,” he said. “But seeing it ahead of time allows those institutions to plan.”

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