Open this photo in gallery Winnipeg paramedics dressed in protective clothing and wearing masks guide a stretcher carrying an ill woman from a Westjet flight from Vancouver to a waiting ambulance at Richardson International Airport in Winnipeg on Feb. 27, 2020. SHANNON VANRAES/Reuters

Top Canadian health officials say they are going to start actively looking for COVID-19 cases in communities, as mounting evidence suggests that the new coronavirus will soon start spreading more freely in Canada.

“We are actively having conversations right now with provinces and territories on some of the next steps,” Theresa Tam, Canada’s Chief Public Health Officer, said on Thursday. Officials didn’t offer a timeline for when the new surveillance systems will be activated, but infectious-disease experts say they are urgently needed.

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The change comes as COVID-19 cases rise in more countries worldwide. U.S. health officials announced Wednesday what they believe to be the country’s first case of “community spread" of COVID-19, the name of the disease caused by the new coronavirus. Community spread refers to a case that is not linked to recent travel to China, Iran or other countries experiencing an outbreak. And it’s significant because it’s the first concrete sign that the virus may be gaining a foothold in North America.

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Last week, B.C. officials announced a case of COVID-19 in a traveller returning from Iran, which came as a surprise as that country had not reported many cases of the disease. As of Thursday, several people with links to travel to Iran have tested positive for the virus in Canada.

Thursday night, Quebec Health Minister Danielle McCann announced the province’s first presumptive case.

Open this photo in gallery Chief Public Health Officer of Canada Dr. Theresa Tam speaks at a press conference in Ottawa, on Sunday, Jan. 26, 2020. Justin Tang/The Canadian Press

The evolution of the outbreak signals that provinces must shift from passive testing on patients who approach the health-care system with symptoms of the disease, to an active surveillance model. Under an active approach, all patients with severe respiratory disease whose cause is unknown could be tested. Provinces could also set up sentinel surveillance sites, where patients who visit clinics in virus hot spots, such as Vancouver and Toronto, would be tested for the disease.

“It’s basically canary in the coal mine surveillance,” said David Fisman, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health. “You pick a few places you think are likely to be where the thing shows up and you focus on them.”

Allison McGeer, director of infection control at Toronto’s Mount Sinai Hospital, said one of the main challenges in setting up an active surveillance system is ensuring laboratories aren’t overwhelmed and vital testing equipment is conserved.

“It’s a real challenge to try to balance all of those things,” Dr. McGeer said.

In an interview on Thursday, B.C.'s provincial health officer Bonnie Henry said she’s working with colleagues to determine what that active surveillance system should look like. Officials are still focused on detecting and containing the spread of the virus, so they must balance that priority with the importance of looking for potential cases in the community, Dr. Henry said.

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Open this photo in gallery British MColumbia Minister of Health Adrian Dix and Dr. Bonnie Henry, provincial health officer, speak to the media on the novel coronavirus in Vancouver, British Columbia, January 31, 2020. DON MACKINNON/AFP/Getty Images

“We are looking at how do we maintain our focus, intense focus, on containing and delaying, but having a better sense of … is there community transmission that’s ongoing?”

Dr. Henry said officials may add COVID-19 testing to the province’s existing influenza surveillance networks, under which a certain number of patients are tested to detect the spread of viral infections. The province is also considering automatically testing anyone who is admitted to the hospital with a severe respiratory illness.

In the meantime, the province will continue testing anyone with symptoms who has a link to recent international travel, she said.

Dr. Henry said it’s unlikely that COVID-19 is already spreading widely in Canada, as existing surveillance networks likely would have detected that new pattern.

Ontario’s Medical Officer of Health David Williams said Thursday that provincial and federal officials were discussing the logistics of expanding the number of people being tested for the disease, such as moving to testing more people with flu-like symptoms who show up at hospitals or clinics.

Open this photo in gallery Dr. David Williams, the Chief Medical Officer of Ontario (C) speaks as Dr. Eileen de Villa, Medical Officer of Health for the City of Toronto (L) and Dr. Barbara Yaffe, Ontario's Associate Chief Medical Officer of Health (R) listen during a press briefing on the coronavirus at Queens Park on January 27, 2020 in Toronto, Canada. Cole Burston/Getty Images

The number of tests is going up now regardless, he said, as more countries are added to the list of those reporting new cases. He said the province is testing about 50 or 60 cases a day now, but can handle 1,000 tests a day if needed.

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“You want to be planning ahead, not reacting to it,” Dr. Williams said at a briefing.

The need to actively look for cases in Canada is growing more urgent, Dr. Fisman said, especially considering the virus may be spreading at the community level in the U.S. While there’s only been one unconfirmed instance of possible community transmission, Dr. Fisman said there’s good reason to be concerned. For instance, the U.S. has experienced problems with its testing kits, meaning very few people have been tested for the virus there, in comparison with other countries.

“Our major vulnerability is not Iran. It’s the United States,” Dr. Fisman said.

With a report from Jeff Gray and The Canadian Press

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