Why coronavirus testing strategies are changing as numbers spike

After months of effort to increase testing capabilities in Canada, some provinces have moved to restrict coronavirus testing as cases soar in many regions.

Ontario and Alberta are no longer testing asymptomatic individuals, with some caveats. Experts agree there’s value in narrowing the testing focus at this point — but it comes at a cost.

“The changing test criteria makes it really, really hard to know what is actually happening in terms of transmission,” said Ashleigh Tuite, an infectious disease epidemiologist and mathematical modeler with the University of Toronto’s Dalla Lana School of Public Health.

“That’s a huge limitation and a huge challenge we’re facing.”

Ontario’s labs have the capacity to process more than 45,000 COVID-19 tests daily. While that’s still short of the province’s goal of around 50,000 by mid-October, recent daily testing numbers fall far shorter.

This week alone, the province reported 24,000 tests on Tuesday and just over 36,000 on Wednesday. Flashback two weeks — the number peaked at more than 43,000 on Oct. 9.

“I recognize that it had to be done,” Tuite said, of restricting testing. “But makes it really difficult to answer, ‘Well, what’s happening?’”

Ontario vs. Alberta

Ontario tightened testing qualifications in September. Citing crippling lineups at its assessment sites and a hefty backlog of uncompleted tests, the province decided to only test people with symptoms, those who have been exposed to a case, and high-risk workers.

Low-risk asymptomatic people can still get tested at pharmacies, but there are caveats — testing is limited to those with loved ones in long-term care homes or close contacts of a case.

The change was significant for a province that spent months saying anyone who wanted a test could get one.

It comes with “downsides,” but it was the right reaction to a pandemic curtained by limitations, according to Alon Vaisman, infection control and infectious disease physician at the University Health Network in Toronto.

“Once you start testing a lot of people simultaneously, you lengthen your turnaround times. You’re harming the very people who are the core of the pandemic, by testing people who don’t need to be tested,” he said.

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“In an ideal world we’d have unlimited access to tests, turnaround times would be short. In reality, we don’t.”

Alberta, which also stopped asymptomatic testing in September, extended that this week to pharmacies.

Freeing up lab space was only part of the decision. The province’s data has increasingly shown that asymptomatic individuals, without known exposures, are not driving the spread.

“Only about one in 1,000 people — with no symptoms and no exposure — has tested positive on average over the past seven months,” said Dr. Deena Hinshaw, Alberta’s chief medical officer of health.

The pivot makes “total sense,” said Dr. Isaac Bogoch, an infectious disease specialist and epidemiologist based out of Toronto General Hospital, but “we have to appreciate that there will be some limitations to the data” we see from here on out.

“By doing more focused testing, we don’t have as good a picture as to what the ground truth is,” he said.

“Better data provides for better public health responses. Some people say these numbers are useless, but nothing could be further from the truth. It’s not perfect data. So what? We have to interpret it.”

Testing down, positivity up

Despite fewer tests being completed, tests are finding more positive cases more often.

When testing numbers are inconsistent or fluctuate, experts agree the per cent positive rate — or the percentage of all coronavirus tests performed that are actually positive — should be the focus.

That number should be kept as low as possible, said Tuite. The higher it is, the more likely cases are being missed.

As of Oct. 21, Ontario’s per cent positive rate sat around 2.4 per cent. It should typically hover anywhere between one and five per cent. In April, it was around 12 per cent.

“When it gets high, it suggests you don’t have enough testing happening in your population,” she said.

“If you have increased positivity and decrease the number of tests, you can’t infer a lot from those trends. It doesn’t necessarily tell you where the problem lies.”

But per cent positivity is inevitably going to go up, said Bogoch.

“With more focused testing, the people coming in are more likely to have the infection because you’re eliminating completely asymptomatic people,” he said.

“So we can infer from the data what the picture is, but it won’t be as clear. Is this catastrophic? No, it’s not. It’s not helpful, but it still provides meaningful information that we can follow. We just need to interpret it slightly differently.”

Looking to recently reported cases alone, Tuite said she’s “incredibly” hesitant to draw any conclusions. Nor does she suggest anyone do so on their own.

“There’s just too much underlying noise in the system because of all these moving parts.”

Problems with appointment-only

Experts say the biggest barrier is not the focused criteria of testing, but the appointment-only system.

Not only does it impede those who don’t have regular internet access from booking, but the average three to four-day wait to get an appointment is also a deterrent, said Tuite.

“People are reluctant,” Tuite said. It reflects a “systems problem,” she continued, which comes with consequences.

For one, the move to online booking makes it nearly impossible to decipher what each assessment center is doing now versus what they did in September.

“As frustrating as those lineups were, it was a marker,” she said. “We know there’s an online booking appointment, but have they reduced the number going through each day?”

It’s also resulted in a no-show problem. Several Ontario hospitals are experiencing no-shows since switching to the appointment-only system, with hundreds of slots going to waste.

“People are trying to get a test, some are booking multiple appointments to try and get somewhere more quickly,” Tuite said. “I don’t blame people for not showing up. Each testing site has its own system, so cancelling appointments is complicated, it doesn’t seem to work right now.”

However, none of this means we’re necessarily “testing less,” she said.

The number of tests any province is able to perform each day is “much higher” than it was at the onset of the pandemic. In fact, she believes the strategy will change again once Canada gets access to rapid tests and at-home tests. Asymptomatic testing will likely be reintroduced, she added.

“This just reflects the reality of where we’re at in the pandemic,” said Tuite.

“When case numbers are low, we can be expansive. When they’re high, we need to be more restrictive.”

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