Canada has tested more than 50,000 people for Covid-19. Is that enough?

In Ottawa on Wednesday, chief public health officer Dr. Theresa Tam once again stressed the need to flatten the curve of the virus' spread, pointing to a "sharp rise in cases" during the past week. "This is a signal there is some degree of community spread," she said. "Our time to act is now."

As of Wednesday evening, Canada had recorded nearly 730 confirmed and presumptive cases of Covid-19 and nine deaths, including a first death reported in Quebec earlier that day.

Though the numbers are clearly increasing, health experts say it's hard to know how many cases there actually are in Canada, since not everyone with symptoms is being tested. Butthey disagree about how much the real numbers matter. Some point out that the available data shows the rate of spread, if not the total number of people infected, and say as long as people with symptoms self-isolate, Canada has a chance to slow transmission of the virus and prevent hospitals from being overwhelmed.

Others counter that people are less likely to self-isolate if they don't know whether they have Covid-19, and argue it's much harder to control the virus when you don't know exactly where it is.

David Fisman, a professor of epidemiology at the University of Toronto's Dalla Lana School of Public Health, said testing is the best way to get control of an epidemic early. By the time people start to die, he said, there have likely been generations of transmission that have gone undetected. "And that's how you get completely hosed by this," he said.

"The testing is kind of our eyes and ears in terms of what's happening. ... I think we're missing a ton of this stuff."

Fisman said the real number of cases in Canada could be much larger than the number on the books. "We have the sense that our positives are increasing exponentially," he said. "The question is what fraction of the true total cases does that represent."

Moreover, the cases being confirmed today are likely people who got sick a week ago or more, said University of Toronto epidemiologist Dr. Jeff Kwong. "In an ideal world, we would be testing everybody," he said. "It's just the reality is we don't have the resources to do that."

Ottawa's medical officer of health, Dr. Vera Etches, has warned there could be hundreds of undiagnosed cases in the city, though there is still no proof of community transmission. Fisman said that may well be the case in many Canadian cities.

Even if the confirmed cases are a significant underestimate, though, they still give a sense of the virus' trajectory, said Dr. Brian Conway, medical director of the Vancouver Infectious Diseases Centre. "I think that as long as we keep doing the same thing ... the numbers from one day to the next are telling us something about how the epidemic is growing," he said.

Canada is "actually doing a really good job" at testing, given limited resources, said Jason Kindrachuk, assistant professor at the University of Manitoba and Canada Research Chair in emerging viruses. "I don't think the overall accuracy of the definitive numbers is really important at this stage," he said, pointing instead to the importance of social distancing and self-isolation to flatten the curve of the virus' spread.

Still, Dr. William Cherniak, an emergency room physician who has been testing patients for Covid-19 for about a month, said the ideal solution would be a test that people could administer themselves. "My thing is always that knowledge is power," he said. Self-isolation would be effective "if people really stayed at home for 14 days if they had the symptoms," he said. But if they haven't been diagnosed with Covid-19, he believes, they're less likely to take those instructions seriously.

On Wednesday, Health Minister Patty Hajdu announced Canada has approved two new diagnostic tests to allow provincial labs to expand testing."Early diagnosis is a critical component of slowing down the spread of the illness and Canadians can be encouraged that Canada has been leading in terms of our testing capacity," she said.

Certainly, Canada has been doing more testing than the U.S., relative to population size. Tam said Wednesday that more than 50,000 people have been tested for Covid-19 in Canada. Meanwhile, the COVID Tracking Project, a volunteer-run accounting of every coronavirus test administered in the U.S., was reporting a total of about 76,000 tests on Wednesday evening, for a population 10 times the size of Canada's. Still, Canada's efforts don't compare to the work being done in South Korea, which now has the ability to test up to 20,000 people a day.

What many Canadians are watching for these days is whether this country is on the same trajectory as Italy was a few weeks ago, before its hospitals were flooded with patients needing emergency care.

If Canada has any chance of avoiding that, Kindrachuk said, now is the time to take social distancing seriously, regardless of the exact number of cases. "It's the calm before the storm in a lot of ways. We cannot become complacent," he said. "If we don't do anything different, we know where this is going."