Interpreting COVID Caseload In Canada

"I think minimizing right now is a real mistake. People are not wanting to believe that this is a thing, because I think they don't want to return to the state we were living in earlier in the year. That's a dangerous path to take."

"The threshold for what we consider high on percent-positivity probably should be considered different now than it was in the spring."

Dr.Lynora Saxinger, University of Alberta

"We are still screening asymptomatic people, but these are people we have a reason to believe were exposed, and that seems to capture most of the cases."

"So we have to always be reacting to what is coming and not necessarily what's happening today."

Dr.Craig Jenne, infectious diseases researcher, University of Calgary

"There's been a definite increase in the number of people who are infected. It isn't just because they're testing more."

"That's kind of the tip of the iceberg [hospitalizations creeping into triple digits]. It ... tells you there's way more community transmission than you might expect."
Dr.Ameeta Singh, infectious diseases specialist, Royal Alexandra Hospital / University of Alberta

 

"[There is a host of] very clear, accelerating trends [in places like Toronto, Peel and Ottawa. Ontario is now imposing stricter measures in those regions to clamp down on the situation, as a record 939 new cases were recorded Friday]."

"The curve continues to increase in terms of its steepness."

"[The province is seeing] a dramatic growth in the percent of tests that are positive."

"In worst-case scenarios, it crosses other thresholds that lead to the reduction of access to hospital care."

"It's there in that older population [the increased positivity rate] where the consequences for health and the consequences for the health system are most severe."  

Dr. Adalsteinn Brown, adviser to Ontario government

 

"There's not a perfect, single metric that's going to give you a perfect sense of what's happening in terms of transmission."
"We certainly shouldn't be looking at the reported case numbers alone. They've become very difficult to interpret."

"The challenge with all of these is you can't really look at them in isolation. But I think the signal we're seeing right now in terms of increases in hospitalizations and people being admitted to ICUs really are indicators that cases are increasing in the community."

"So basically, [it means] you're at a point where you are going to be struggling to understand and identify where people are getting infected." 

Ashleigh Tuite, epidemiologist, University of Toronto's Dalla Lana School of Public Health

Ontario instituted measures like shutting down indoor dining in some areas of the province Friday in an effort to curb the spread of COVID-19. (Evan Mitsui/CBC)

A recent surge in COVID-19 cases surpassing a spike that occurred last spring, warns infectious disease specialists, must not be given short shrift as representing a mere byproduct of increased testing. Data publicly posted in Alberta, British Columbia, Ontario and Quebec over the week ending April 21 for that specific single week, and another ending October 6 meant to obtain a sense of just how the two case surges compare was compiled by the Canadian Press. The results do not inspire confidence.

In Alberta daily cases are now two percent higher in the most recent period in comparison to the week in April, while Ontario's were 13 percent higher, Quebec's 14 percent higher and cases in British Columbia were more than tripled the mid-to-low, double-digit numbers experienced in that province in April. As an early leader in increased testing Alberta took close to four times as many swabs during the week of October than in the April week, while B.C.'s daily testing grew eightfold, Ontario and Quebec performed roughly 4.5 times as many weekly swabs in the fall week as compared to the spring.

The positivity rate representing the percentage of tests coming back positive, in all four provinces dropped markedly between spring and fall surges. Quebec averaged some 6,300 daily tests and 930 new cases in April with a positivity rate during that period of about 15 percent. More recently in October as Quebec coped with five consecutive days of new cases in quadruple digits, its positivity rate sat at about four percent.

In Ontario, dealing with a large backlog of swabs awaiting analyzing, the province posted an official daily positivity rate of two percent for October 7, reduced from the roughly six percent range it had posted in mid-April. The positivity rate in Alberta dropped to one percent from close to five percent, and B.C.'s fell to 1.3 percent from four percent. Yet experts indicate that the lower positivity rates are no cause for comfort. They point out that early testing was largely limited to people with specific symptoms and those who came into close contact with them.

Test now tend to service a much broader portion of the population, many with mild symptoms or asymptomatic cases. Testing among people with no suspected exposure or symptoms in Alberta over the summer unearthed very few new cases, pointed out infectious diseases researcher Dr. Crag Jenne, at the University of Calgary. Testing has since been tightened to those at higher risk, or with upcoming travel, by the province. Yet, pointed out Dr.Jenne, today's results reflect viral transmission of ten to 14 days earlier.

Trends in hospitalization are seen as a lagging indicator eyed with concern by experts. For example, in Ontario, hospitalization began creeping into the triple digits roughly two weeks earlier. The percentage of people testing positive grows in a "very sharp way", according to Dr.Brown, against the backdrop of "relatively strong" testing numbers. According to provincial data released Friday, some regions in Ontario are far above the three percent positivity rate, recognized as an international benchmark reflecting a serious problem.

People wait in long lineups for a COVID-19 test at a drive-thru testing centre in Toronto on Sept. 28. The province has since moved to an appointment-only testing model, though a testing backlog remains. (Evan Mitsui/CBC)