Hitting reset on parameters for COVID testing
In the first wave of COVID-19 the goal of testing was to cast the net wide, to find hidden cases and get a feel, Queen’s university’s dr. Gerald evans says, “for how broadly based the infection was in our society.”
experts pushed provinces like Ontario to increase testing from an insignificant 5,000 a day to get a better picture of the virus, and how many “susceptibles” remained among us.
Alberta and Ontario soon after opened up testing to anyone who would like to be tested, even if they had no symptoms or no known contacts to a confirmed case — the same people now straining overloaded pandemic testing systems.
Alberta announced Thursday it’s hitting the reset button, temporarily halting broad asymptomatic testing in anticipation of a fall surge in demand for tests as schools reopen and cold and flu viruses make their annual arrival.
Since may 29, Alberta has completed some 233,000 tests on people showing no symptoms, with only 0.07 per cent returning positive — about 163 cases. Alberta tested an average 13,625 people a day over the past seven days, nearly six times the 2,380 people tested per day in march and April. The cost per test? About $74.
Labs across Canada tested an average of 47,111 people daily over the past week, with 1.4 per cent testing positive.
Ontario, meanwhile, will soon be getting “a couple thousand” new COVID-19 test centres at pharmacies for those without symptoms, Premier doug Ford announced this week. The idea is to ease congestion at COVID assessment sites. The province is going to ramp up testing “like you’ve never seen before,” Ford pledged. Ontario has increased its capacity since the early days, from 5,000 to 25,000 to 30,000 tests per day, with plans to move up to 50,000 daily and beyond.
but evans and other experts say, if anything, Ontario should reel in testing people with no known symptoms and no known contacts. The focus should be on diagnosing people with symptoms, quickly. evans and others are less interested in the asymptomatic, norisk contact people, “because they provide less information at this point in the pandemic, and we know we’re going to have lots of people now with common cold symptoms who are going to present for testing, and we need to be able to find the ones that are real COVID so we can control them with contact tracing and isolation.”
evans, chair of the division of infectious diseases at Queen’s, says the public has been galvanized by the idea that asymptomatic COVIDS accounted for 40 per cent of infections. “We know that absolutely is not true,” evans said. Truly asymptomatic people with COVID-19 are well below 20 per cent, evans says, “probably in the range of 10 to 15 per cent of all cases.”
People with no symptoms but who have been socially active have a much higher probability of being positive. “The person who has no symptoms who has really been good — no risk contacts — the probability we’re going to find out they’re positive is going to be extraordinarily low,” evans says, in the ballpark of less than one per cent.
Part of the problem is the feedback loop: confirmed cases are increasing, the media report the rising case counts, people worry and start showing up at testing centres.
Layered on top of the anxiety are children returning to school and public health rules set up so that every child with a cough or potential symptom of COVID is sent home and tested. All of it is driving enormous traffic through testing centres, and with thousands of new testing sites in Ontario for asymptomatic set to open, there is still the issue of having enough lab capacity to process them.
If the new sites still have to use the same methods, the same nasal swabs specimens, the same expensive molecular tests that have to be done at centralized labs, “you’re going to face the same issues in terms of turnaround times, lab capacity, machines running out of reagents,” says dr. Zain Chagla, an infectious diseases physician and associate professor at mcmaster university in Hamilton, Ont.
until rapid, cheap tests are approved by a federal government that appears in no great hurry to do so, the priority must be people with symptoms and those who have had significant exposure, experts say. “by flooding the system with asymptomatic testing, we jeopardize that response,” says mcmaster university infectious diseases specialist dr. dominik mertz. The more bottlenecks, the longer the turnaround times for results, the longer the delay in reacting to a positive test.
Alberta will still be offering asymptomatic testing of high-risk groups, including health-care workers, teachers and staff, people living in long-term care and the homeless.
b.c.’s provincial health officer, dr. bonnie Henry, has resisted testing people with no known symptoms or known contacts, arguing the evidence doesn’t support it.
Some say we need to de-emphasize the focus on daily numbers. The current gold-standard swab test used to detect viral RNA, a sticky molecule, can remain positive for weeks after infection. It doesn’t necessarily mean the person is still infectious.
While cases are curving upwards, deaths and hospitalizations have remained low. Over the summer, COVID-19 moved into younger, lower risk age groups, where it’s ramping up. “If it were going to stay in that age group, that would be great,” says university of Toronto epidemiologist dr. david Fisman. “The problem is that it won’t, and we’ve seen this pattern play out now, over and over again — in France, Spain, Florida, Austria.
“One of the great tragedies of COVID is our inability to learn from other places.”