The total number of positive COVID-19 test results is unclear due to discrepancies between the public information put out by the provincial health ministry and the numbers posted by individual local health units.

A Star analysis found that in some cases the numbers reported by the province and local health units match, but in others the numbers are off by as many as one, nine — or in Toronto’s case, 39 — confirmed cases.

The discrepancies are raising concerns that health practitioners and officials, as well as the public, may not be getting the full picture of how the virus is behaving. Experts say robust and timely data is crucial to planning an effective response to the pandemic.

“Epidemiology is about understanding patterns of disease in terms of person, place and time. We want to understand these things so we can predict disease spread, and control it,” said Dr. David Fisman, an epidemiologist and professor at University of Toronto’s Dalla Lana School of Public Health. “This is an unprecedented health emergency; this is the moment that Public Health Ontario was created for after SARS.”

When the Star asked the province to explain the discrepancies, Hayley Chazan, a spokesperson for Health Minister Christine Elliott, said the cases reported on the province’s website are based on information provided by the Public Health Ontario laboratory and certain hospitals that are helping to expand testing capacity.

“While we make every effort to co-ordinate and validate with local public health units, there may in some cases be a lag in information sharing at time of posting,” she said.

The Star reported Wednesday that the number of confirmed and negative cases reported to the public in Ontario each day is roughly four days old or more and that the number of test results the province is waiting for is increasing.

Speaking to reporters Thursday, Premier Doug Ford, in response to a question about the conditions in provincial jails, stressed the importance of data to all his ministers.

“I want to see data because you can’t manage unless you measure,” Ford said, later adding in response to another question that officials need to be “singing off the same song sheet.”

Twice a day, the health ministry updates its website with new confirmed positive cases in Ontario, along with categories for patient age and gender, reporting public health unit, method of transmission and patient status, if available. To date, it has reported 258 confirmed positive cases. More than 100 contain incomplete information with several or all categories labelled “pending.”

But not all of those 258 cases are currently detailed on the province’s central COVID-19 website.

When the province updates the numbers for the first time each day, usually around 11 a.m., the previous day’s data is overwritten, including cases with information “pending,” leaving only details of the newly reported cases online and public, making past positive cases difficult, if not impossible, to track.

Was the patient hospitalized? Had they travelled? If so, where? Or did they have close contact with someone who already tested positive for the virus? None of these remaining questions surrounding the older confirmed cases are answered by the health ministry when it overwrites the previous day’s data.

For example, on Wednesday March 18, the provincial list included three confirmed positive cases in which all categories were listed as “pending.” The next day, all three cases disappeared, never to be updated, when the new cases were reported.

Provincial health officials have said that more than 90 per cent of cases are international travel-related and close contact with travel-related cases, but the information — coming from different places, such as press conferences and various websites — is not comprehensive or compiled in one place.

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The Star was able to rebuild the province’s reporting history by using the internet archive website Wayback Machine and by checking local media reports going back several weeks.

Waterloo resident Doug Johnson Hatlem, who has spent four years collecting public data as a hobby, has for a week also tracked the province’s positive COVID-19 cases as something to do after going into voluntary quarantine following a trip to the United States.

“The best practice in these awful times would be for the province to have a regularly updated full list of each case rather that overwriting the often incomplete initial data each day,” said Johnson Hatlem, who has built his own spreadsheet and made it public.

On Thursday, Toronto Public Health said on its website that it had a current total of 128 cases of COVID-19. Ministry of Health officials have to date reported 89 Toronto cases.

When the Star asked the City of Toronto if it could explain the discrepancy between its numbers and those being reported by the province, Dr. Michael Finkelstein, associate medical officer of health for the city, said in an email that the “number of individuals reported to Toronto Public Health who are infected with COVID-19 is changing quickly” and that the Star should “connect directly with the province on their numbers and process.”

When asked if the city had ever asked the province why its numbers don’t match those reported by the city, Finkelstein said: “We are actively engaged in conversation with the Ministry of Health to ensure consistency in reporting this quickly evolving information.”

To date, health ministry officials have reported 18 confirmed positive cases in York Region. But York’s website listed 27 cases on Thursday night.

Patrick Casey, director of corporate communications for York Region, said the cases on region’s website are “reflective of the cases we currently have.”

Peel Public Health reported on its website Thursday 26 confirmed positive cases. Adding up the cases reported by provincial health officials, that number is 25.

“We cannot speak to the case counts presented on the Ministry website,” said Dr. Lawrence Loh, acting medical officer of health for Region of Peel. “The Peel COVID-19 positive case numbers are accurate at the time of posting on the Region of Peel website.”

Tracey Lauriault, assistant professor of critical media and big data at Carleton University’s School of Journalism and Communication, said the province should provide a daily updated file that includes previous data.

Alison Thompson, a professor at the Leslie Dan Faculty of Pharmacy at U of T, says she suspects the discrepancies are the result of a time lag, a phenomenon that occurred during SARS and caused big problems for the World Health Organization hearing from doctors on the ground.

“It does speak to a problem in terms of the communications piece and they need to fix that because it’s going to engender mistrust. So it’s a good idea to get to the bottom of what is causing the discrepancy,” Thompson said. “Even a time delay can have a big impact on what kind of measures they implement.”