Why the numbers we hear about COVID-19 don’t tell the whole story

Story by CBC Kids News • 2020-05-14 14:55

Expert says it’s not a perfect science

Every day, provinces and territories in Canada release new information about the number of new cases of COVID-19.

We are also getting a regular tally of deaths.

But it’s important to be aware that individual numbers aren’t giving us a clear picture of how the virus is spreading and whether we have it under control.

CBC Kids News spoke to Raywat Deonandan, an epidemiologist and professor at the University of Ottawa, to find out more.

Raywat Deonandan is an epidemiologist, someone who studies diseases in order to prevent them from spreading. (Submitted by Raywat Deonandan)

An epidemiologist studies epidemics (like COVID-19) using math and other types of nonmedical tools.

“We look at the ways that the disease spreads across the population,” he said.

Things to keep in mind

Just because you hear that a certain number of people have tested positive for COVID-19 on any given day doesn’t mean that’s the absolute number of new cases.

There are a few reasons for that:

 Time: It takes time for the tests to come back from the lab so there could be more cases that we don’t have the results for yet.  Some people are asymptomatic: People could be walking around with the virus and not even know they have it.  New testing: It’s also important to note that the testing criteria evolved over time. “If you look at the early days of the epidemic, we didn't have a lot of testing kits,” Deonandan said.  Not all provinces have the same testing criteria: Some provinces are testing more people than others. Alberta, Nova Scotia and Quebec are testing a high proportion of the population. More testing equals more cases.

A man is tested at a mobile COVID-19 testing clinic in Montreal. (Ryan Remiorz/The Canadian Press)

Why the hype around flattening the curve?

We heard that we need to flatten the curve so the hospital system doesn't get overwhelmed.

A good way to know if that’s working is by looking at the number of new cases every day, over time, said Deonandan.

But even this doesn’t tell the whole story, as you can see in this graph.

There was a sudden spike in numbers on May 3 because there was a technical problem in reporting numbers in Quebec that day.

“What matters is over the course of several days, what is the trend in producing new cases,” said Deonandan.

What about the number of deaths?

Some people are looking at the number of deaths, but there are problems with that as well, said Deonandan.

For example, some people may have died of COVID-19 before Canada started aggressively testing people.

A patient is pulled off an ambulance on a stretcher in front of a hospital

Hospitals in Canada have been treating COVID-19 patients, but some people with the disease may never be tested. (Darryl Dyck/The Canadian Press)

Also, some people may have died without seeking medical attention and we wouldn’t know they died from COVID-19.

Other factors to consider

Deonandan also pointed out that testing isn’t a “pure science” and some specific groups of the population may be forgotten.

He used Singapore as an example.

People wearing face masks cross a road along a popular shopping belt in Singapore on May 6. (Roslan RAHMAN/AFP via Getty Images)

“They thought they had their caseload under control. It turns out they're ignoring their entire migrant worker population. And that's where their next outbreak occurred.”

In Canada, Saskatchewan appeared to have very few cases and suddenly there was an outbreak in a northern community.

A person wearing personal protective equipment holding a test tube and a clipboard

Health workers perform COVID-19 tests on residents of the remote First Nations community of Gull Bay, Ont. (David Jackson/Reuters)

At the end of the day, the more people who are tested, the better we will understand the spread. 

Looking for more information on the coronavirus? Check out these videos:

With files from CBC News

TOP PHOTO: (Philip Street/CBC)

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