Health·Second Opinion

Why doctors say we need to cast a wider net for COVID-19 in Canada

Canada's first case of coronavirus not linked to travel suggests we need to expand our surveillance systems to prevent an explosion of new cases, infectious disease experts say.

Community transmission of the virus in Canada signals a new stage in the outbreak

Airline crew members wear masks at Toronto Pearson International Airport on Jan. 26. Non-travel-related COVID-19 cases are now occurring under the radar of Canada's surveillance system, doctors say. (Evan Mitsui/CBC)

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Canada's first case of coronavirus not linked to travel suggests we need to expand our surveillance systems to prevent an explosion of new cases, infectious disease experts say.

The latest case of COVID-19 in British Columbia, a woman in her 50s who has no recent travel history to affected regions worldwide or contact with infected individuals, signals a shift in the spread of the virus in Canada. 

"There's likely at least one other person out there who has this disease or had this disease, and we need to find them," B.C. provincial health officer Dr. Bonnie Henry said Thursday.

Dr. Isaac Bogoch, an infectious disease physician at Toronto General Hospital, said this means there could be more cases in the province that are likely being missed by current screening measures. 

"There is some degree of transmission in B.C.," he said. "We don't know the size and scale of it, but it's definitely there and the goal for surveillance systems would be to help shed light on what the degree of community transmission is." 

B.C.'s provincial health officer, Dr. Bonnie Henry, said health officials are looking for at least one other person in the community who has or had the illness. (Ben Nelms/CBC)

Bogoch said Friday that while it's been important to have systems in place to screen for patients travelling from affected regions, the concern now is how sensitive those systems are at picking up new cases in the community. 

"Clearly something is happening under the radar of the surveillance system," he said. 

"It doesn't mean the surveillance system is bad, it just means that there might be low levels of transmission or the surveillance system has not cast a wide enough net yet." 

Currently, most health-care workers in Canada are screening only people who show up with flu-like symptoms such as fever and dry cough and say they've travelled to any of seven places  — China, Japan, Hong Kong, Italy, Iran, Singapore and South Korea.

An ambulance transports a patient from the Life Care Center of Kirkland, the long-term care facility linked to confirmed coronavirus cases in Washington state. (David Ryder/Reuters)

"We've been looking for people coming into the country with it; we have not been doing widespread community screening," said Dr. Michael Gardam, an infectious disease specialist at Humber River Hospital in Toronto. 

"But, with the announcement from British Columbia, obviously that is going to continue to ramp up." 

U.S. case a concern for Canada

Given B.C.'s proximity to Washington state, provincial health officials are working closely with their U.S. counterparts. 

Henry, the provincial medical officer of health, said one of the eight new cases in B.C. is a resident of Seattle who was visiting relatives in the Fraser Health region when she tested positive. 

"Clearly that is of concern with us," she said. 

But part of what Henry calls the "disease detective work" to trace where the visitor may have contracted COVID-19 south of the border also depends on decoding the genetic sequence of the virus from Washington state's "patient zero" — the initial patient. 

The traditional public-health approach relies on finding cases by interviewing someone who is infected and tracing those they've been in close contact with. Now, scientists also use genetic fingerprinting of the virus to complement efforts to find and isolate patients quickly. 

"If all community-based transmission can be traced back to a patient zero early on in an outbreak, that's usually a good sign," said Matthew Miller, who studies viruses and the immune responses to them at McMaster University in Hamilton, Ont.

The problem is that once the virus is spreading without a clear link to the source of the disease, tracking patient zero becomes less useful for containment purposes.

Canada isn't there yet, Miller said, which is why community surveillance for COVID-19 takes on more importance right now. That's why some hospitals across the country are moving toward testing all patients with flu-like symptoms.

Bogoch said expanding the list of countries to screen travellers from would be ineffective compared to community screening, because the list of places will become unmanageable. 

"It's just going to be an extreme challenge to be able to detect all the imported cases," he said. 

"At which point we're just going to see more and more community-acquired cases in Canada." 

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Dr. Jerome Leis, medical director of infection prevention and control at Toronto's Sunnybrook Hospital, led a study in the Canadian Medical Association Journal Friday on what the early Canadian experience screening for COVID-19 shows us about how to prepare for a pandemic.

Leis said curbing community spread limits the number of infections and reduces the proportion of patients who fall critically ill.

"Hospitals throughout Ontario have stepped up the surveillance … and so we're testing individuals that have not travelled," Leis said. "I think we should be stepping it up further."

In the event of a pandemic with widespread community spread, it's "simply not feasible, nor is it safe," to test everyone, he said. 

"It will lead to overcrowding of hospitals and emergency departments," he added. "That could just further increase the risk of exposure as people are diverted to hallways and have long wait times to be seen."

Instead, Leis recommends building capacity both in hospitals for those who are critically ill with COVID-19 as well as in the community for the majority who have mild illness. 

"Hospitals are not the best place to be assessed and tested for COVID-19," said Leis. 

"We really need to be changing the conversation from a hospital-driven model for people that are concerned about COVID-19, to one that is better supported in the community for the people who don't need hospitalizations." 


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About the Author

Adam Miller

Senior Writer

Adam Miller is senior digital writer with CBC News. He's covered health, politics and breaking news extensively in Canada, in addition to several years reporting on news and current affairs throughout Asia.

With files from CBC's Christine Birak