Ontario quietly changed the way it reports COVID-19 testing data. Here’s why you should care

Ontario has changed the way it's reporting COVID-19 testing data in the midst of the pandemic in a move experts say may skew the true picture of how the virus is spreading in people across the province.

Until this week, the Ministry of Health had been reporting the total number of patients tested for the coronavirus each day. On Wednesday, the reporting changed to include only the number of samples tested per day, and because more than one sample is taken from some patients, it was no longer possible to know how many people had been tested.

This means it is now harder to know the important measure of Ontario's test positivity rate, said Todd Coleman, epidemiologist and assistant professor in health sciences at Wilfrid Laurier University.

Switching how tests are reported changes the positivity rate "very significantly," he said, adding that the province should report both the number of samples tested and patients "to give us an accurate representation of what's happening."

The positive rate - the percentage of people tested for a disease who are found to actually have it - can give a picture of an epidemic's spread, experts say. Over time, as more people become infected, the positive rate should be expected to go up.

But after the switch to the reported data, Ontario's positive rate has fallen sharply. Nearly 10 per cent of patients reported tested Tuesday were positive; that number was less than 6 per cent for samples reported Thursday.

Why does this matter? "Because that's how the disease works," Coleman said. "It's not dependent on each test. Each test that comes back positive doesn't mean a new case."

The reporting change came on the same day that Premier Doug Ford pledged testing in Ontario would hit the 8,000-per-day mark after weeks of falling short of that number, even as provincial labs expanded capacity to meet increasing demand. On Thursday, the Health Ministry reported that 9,001 tests had indeed been completed - up significantly from previous days. But because of the reporting change, it was unclear whether many more people had actually been tested, or if the jump was merely the result of the switch.

"Well, today we're at over 9,000 COVID-19 tests. We've hit our first target," Ford said at his daily news conference Thursday.

The premier did not explain that the provincial tracking data - publicly available online - had been quietly changed until he was pressed by a reporter.

"First of all, they're accurate numbers and I'm going let the minister explain it," Ford said, turning to Minister of Health Christine Elliott.

"We're testing some people a couple of times, maybe a week later. But they should still count as a test and that all depends on their situation but I'll pass this over to the minister," he said.

Elliott downplayed the data change.

"The number of people who have been tested more than one time are not significant," she said.

"What's more important is we've really expanded the number of people we're testing in different locations; in long-term health care homes; front-line health care workers; working with Indigenous communities, working now with essential service workers."

Colin Furness, an infection control epidemiologist at the University of Toronto, said Ontario's data flip-flop was a "political decision" to showcase its newly increased testing ability.

"It's odd because what you are actually presenting, in a sense, is less data by saying we're going to count the number of tests but not the number of people tested," said Furness, who has expertise in vulnerable populations and systemic issues in long-term-care facilities.

"You're deliberately saying, 'We've got these two data points and we're only going to hand you one.' Less information is never a good thing," he continued.

"It seems to me it's a political decision to report the larger of the two numbers, to say, 'Look at all the testing we've done,' because there's been a lot of discussion around testing capacity. So I think the premier's office may want to demonstrate, 'We've built this testing capacity and now we're using this testing capacity,' and I think it's a political consideration."

At the news conference, Elliott also said the data change brings Ontario "more in line with what most other provinces are doing and the way they're reporting, principally British Columbia."

Canadian provinces are not uniform in their data collection. Some use totals for people tested, some use total samples tested. Alberta and Saskatchewan track both.

"Both are important," said Isaac Bogoch, an infectious disease expert based out of Toronto General Hospital.

"I bet that data (in Ontario) is available and I think it would be helpful to have both, because some people are testing multiple times a) because they tested negative but they still have symptoms so they get tested again; b) some people are health-care providers and need to get tested more than once to make sure that they test negative so they can go back to work," Bogoch said.

"People tested is important because we want to know how many people have this infection. Samples tested is important because that gives us an understanding of what the lab capacity is. So I think they're both important and I'd want both data points."

Kenyon Wallace is a Toronto-based investigative reporter. Follow him on Twitter: @KenyonWallace or reach him via email: kwallace@thestar.ca

Mary Ormsby is a reporter and feature writer based in Toronto. Reach her via email: mormsby@thestar.ca