Canada's official guidance on the novel coronavirus has been to test patients who recently travelled to affected areas, but some doctors and hospitals have expanded testing on their own, finding the first in a series of patients linked to Iran before the scale of the Iranian outbreak was known.
The Canadian approach, which let front-line staff exercise judgement in looking for the virus, diverged from the United States, which said only on Tuesday that any American could be tested.
One unlikely catch was British Columbia's sixth patient, a woman in her 30s whose test results were announced on February 20. She had recently travelled from Iran, but as the country had only disclosed its first cases on February 19, she would not have been flagged under federal guidelines in use at the time.
But the woman had been on multiple international flights, so a clinician in Vancouver tested anyway, said the province's health officer Bonnie Henry at a recent press conference.
"We have always said that if a clinician has a concern about somebody and they have symptoms that could be Covid-19, that we would allow that testing," she said.
The day after the case was found, Theresa Tam, Canada's chief medical officer, told reporters "imported cases linked to Iran could be an indicator that there is more widespread transmission than we know about."
By March 3, BC had found five more cases linked to Iran, and more were identified in Ontario.
Every case that is caught can prevent a chain of new infections. Even so, on Thursday BC said it had what could be Canada's first case of community spread. Canada has confirmed 45 cases by Friday.
Canada's federal government testing guidance is currently focused on travel to a list of locations that has lagged the spread of the virus. On Friday, Washington state was not listed, even as it battled an outbreak that has killed 12 people.
But provinces are not bound by the guideline. BC, which shares a border with Washington, is now telling healthcare providers that anyone who would usually be tested for influenza or respiratory syncytial virus, another common illness, should also be tested for the novel coronavirus.
Ontario has stuck with the federal government's list of affected areas, but says clinicians can test other patients they feel are at risk.
Surveillance testing, a separate process focused on patients who no one has identified as at risk, is also ramping up. BC has added the virus to its flu surveillance program, which tests a sample of patients seen by a selected group of clinicians to better understand how the flu spreads. Ontario is piloting a similar program.
Kevin Katz, medical director of Toronto's Shared Hospital Laboratory, who is participating in the Ontario pilot, said on Thursday his site had sent 20 to 30 samples a day for just under a week and so far all were negative, uncovering no evidence of widespread community transmission.
Lab capacity has made testing possible. Canada has three government labs that can confirm infection, and Ontario has said its lab alone could handle up to 1,000 samples a day. Washington state said on Wednesday its state lab can only test about 100 patients a day.
In Ontario, several major hospitals said they are also running diagnostic tests more broadly than the province requires.
"The people who are having to respond to this on the front lines are always going to have to be more nimble," said Susy Hota, director of infection control at the University Health Network.
"We're going to see things shifting a little bit quicker."