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Ontario’s record-breaking daily COVID-19 case numbers, positivity rate don't tell the whole story, doctor says

Elisabetta Bianchini
·4-min read
A map of Ontario shows a conceptual image of the spread of COVID-19 in the province. Dr. Sumon Chakrabarti, an infectious disease specialist, says the daily case numbers and positivity rate are important to keep in mind, but not the only way to track spread in the province.

All eyes are on daily COVID-19 case data, test positivity and the number of vaccine being administered as Canadians push through this third wave of the pandemic, but actually understanding what the data means is another important aspect of navigating COVID-19.

On Tuesday, Ontario's test positivity exceeded a record 10 per cent for the first time, with 42,167 tests completed, going back down to 8.6 per cent on Wednesday, with 54,211 tests completed in the past 24 hours, and eight per cent on Thursday, with 65,559 test completed in the last day. New confirmed COVID-19 cases on Thursday totalled, up from 4,156 the day before. The seven-day average for cases in Ontario is currently 4,208.

There are 1,932 people in Ontario hospitals with COVID-19, including 659 in ICU.

To date, 3,528,404 doses of COVID-19 vaccine have been administered in Canada, with 339,491 people fully vaccinated and 105,430 daily doses were administered as of Wednesday at 7:00 p.m.

How should we interpret the daily COVID-19 case counts and test positivity?

While the raw number of COVID-19 cases is reported daily, infectious disease expert Dr. Sumon Chakrabarti identified to Yahoo Canada that this number has to potential to have a "bias" or fluctuations if there are any large sweeps of testing performed for individuals in a particular setting.

For example, if cases start to be identified in meat processing plant, a factory, or another particular workplace, testing for those individuals in the same time period could lead to a significant increase in the daily reported case counts.

"I think people are looking at that raw number and they're using it as a surrogate for their own risk, where that's not necessarily the case," Dr. Chakrabarti said. "That's why I think per cent positivity is a good thing to look at as well."

While test positivity is something to be aware of, in conjunction with case count, it is also susceptible to day-over-day variability.

One example would be asymptomatic testing in schools. With spring break and schools closed for the foreseeable future, the gap in that data, with Dr. Chakrabarti identifying that the positivity rate for children has been relatively low, can impact that daily reported number.

Whether you're looking at case and/or test positivity data, the infectious disease expert stressed that the trend is more important than a single-day result.

"There's no doubt that the...cumulative trend is much more reliable," he said. "When the [data] is kind of trending upwards, you know that...even though the number might be this, there's probably a lot more that we are not detecting in the community."

He also identified that as we move through the COVID-19 pandemic, case counts will be a less significant metrics.

"We're already starting to see the case count and deaths are now starting to kind of decouple and eventually, we're going to see case counts and hospitalizations decouple as well," Dr. Chakrabarti said. 

"These are all kind of indicators that the vaccination is working."

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What should we consider when we look at the daily COVID-19 vaccine data?

Dr. Chakrabarti stressed that it is important to ramp up the number vaccines administered each day but added that looking at the communities receiving these vaccines is an important consideration when trying to understand this data.

For example, vaccinating seniors in long-term care homes has made a significant impact on the number of these individuals who have more recently been admitted to hospitals due COVID-19 complications.

"I think that what we do need to look at is who is getting vaccinated," Dr. Chakrabarti said. "We've given a significant number of community dwelling 70 and 80 year olds vaccine and...you're seeing [much less of them in hospitals] than you did in the first and second waves."

He added that moving forward with vaccinating higher risk populations in Ontario will lead to a core goal of dropping in the number of hospitalizations and deaths, which should lead to a loosening of restrictions.

"If we have a vaccine that prevents hospitalizations or at least significantly reduces it, this is our ticket out of restrictions," Dr. Chakrabarti said. "The reason we're doing any of these restrictions in the community is an attempt to try to slow transmission so the [hospitals] can actually deal with the load."

"Is the vaccine necessarily going to prevent you from getting COVID? No, because some people might get COVID but you're going to get a sore throat, you're gonna get a fever and you're in bed for one day, it's way better than being admitted to hospital for a week."