Open this photo in gallery People walk towards a Covid-19 Assessment Centre at Michael Garron Hospital, in Toronto, on March 15, 2020. Christopher Katsarov/The Globe and Mail

The move by more provinces to reserve COVID-19 testing for the highest risk cases, such as people with severe illness or health-care workers, could complicate Canada’s fight to stop the spread of the disease here, according to some infectious-disease experts. If health officials aren’t going to do broad testing, they say, then the country needs to get more serious about ensuring people self-isolate and avoid others in order to reduce the impact of the coronavirus.

Until now, Canada has focused most of its testing on individuals with COVID-19 symptoms, such as fever and cough, who travelled out of the country or who were close contacts of those who tested positive. This weekend, however, British Columbia and Ontario officials said they were narrowing testing to a more select group, including people sick enough to require hospitalization, long-term care residents, health-care workers or people who live on a First Nations reserve. Public Health Ontario said on its website part of the reason for the shift is to ensure there is no shortage of test kits.

Michael Gardam, chief of staff at Toronto’s Humber River Hospital and an infection-control expert, said the change signals health officials believe the opportunity for containing the disease has passed and that the best course of action is to aggressively push social-distancing policies.

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“That window is largely closed,” Dr. Gardam said. “Now, it’s really about the social distancing and keeping people away.”

But others say testing remains a key component in reducing transmission of COVID-19. On Monday, the director-general of the World Health Organization admonished countries for failing to scale up testing in a way that could help them mitigate and control outbreaks.

“You cannot fight a fire blindfolded and we cannot stop this pandemic if we don’t know who is infected,” Tedros Adhanom Ghebreyesus said.

Peter Phillips, an infectious-diseases physician at St. Paul’s Hospital in Vancouver and a clinical professor at the University of British Columbia, said Canada should be testing more people, including those with mild respiratory symptoms who haven’t travelled outside Canada or come into contact with someone who has tested positive for COVID-19.

“If we let this continue to spread in the community and we’re not going after these individuals with aggressive testing, we’re not going to have a handle on it,” Dr. Phillips said. “You cannot contain it if you don’t know where it is.”

Canada had administered about 25,000 COVID-19 tests as of Sunday, said Theresa Tam, the country’s Chief Public Health Officer. The numbers vary by province, with Ontario approving nearly 10,200 people for testing as of Monday morning. Ontario also ran 1,542 tests as part of a “sentinel surveillance” program, which looks for COVID-19 in patients who are experiencing flu-like symptoms. B.C. had tested 6,326 people as of Friday. Saskatchewan had only performed 499 tests as of Saturday, while Newfoundland and Labrador had done 161 as of Monday.

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In the United States, only about 37,000 tests have been done as of Monday, even though its population is 10 times the size of Canada’s.

Despite this, Canada’s testing figures are nothing to celebrate, according to some experts. For instance, they’re a far cry from South Korea, which is able to do 10,000 tests a day, an approach that is credited with helping the country contain the outbreak and avoid the type of spike in cases seen in places such as Italy.

David Fisman, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health, has argued for weeks that the limited testing being done in Canada would put the country at a severe disadvantage. And that means officials must adopt population-wide strategies to stop the spread of disease, primarily by focusing on social distancing, he said.

Barbara Yaffe, Ontario’s deputy chief medical officer of health, said in an interview Friday that it isn’t necessary to identify every mild case of COVID-19, especially if a possible shortage of testing supplies becomes a real one.

“There’s no specific treatment for COVID-19,” Dr. Yaffe said. “[Testing] won’t make much difference to their particular treatment or what’s done for them.”

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It’s imperative, she added, that anyone who develops a fever and dry cough, the telltale symptoms of COVID-19, stay home and self-isolate for 14 days unless they become so sick they need hospital care, regardless of whether they are able to get tested.

“If they’re not over 60 and they don’t have underlying health conditions, they’re probably going to ride it out and be fine,” Dr. Yaffe said. “But they shouldn’t go out. If you’re sick, don’t go out.”

It’s unclear whether those messages are trickling down to the public. In recent days, many people have continued flooding provincial health lines with calls about whether they should be tested and testing sites have been swamped with requests.