Ask an epidemiologist what it would take to return to some version of normal as we wrestle with the novel coronavirus, and the answer usually involves doing a lot of testing — a vast amount of testing.
The more we know and the faster we know it, the more we can deal with local outbreaks as they flare up, as they unavoidably will.
The problem, though, is that there aren’t enough tests, and there isn’t enough ability to process them.
One workaround is pool testing. The concept is simple: get swabs from a group of people, take samples from those swabs, and then test them together.
If there’s no trace of coronavirus in the group sample, you don’t need to test the individual swabs. If the group sample is positive, then go to work on finding the person, or people, who are positive.
“Pool testing is a very, very smart innovation to reduce what is really a bottleneck in managing COVID, and that is limited testing,” says Colin Furness of the University of Toronto.
The University of Toronto’s Vivek Goel sees pool testing as the key to being able to reopen group settings like university residences.
“If I have 40 students on a floor, at the current cost of doing the viral testing it would be very expensive to do regular testing on a weekly or monthly basis,” he says.
“But if I pooled the samples for the entire floor, I get that cost down considerably.”
The West African country of Ghana has been coping with a test shortage through pool testing, Goel says.
“As we open up more places, testing is going to be an important strategy, and we have to find ways of doing it in a very efficient way.”
“People say that everyone who wants a test should be able to get it. That’s a nice thing to say in theory, but to do tests on the entire population of Canada on a weekly basis would completely blow up the economy.”
There is a potential downside, according to both Benoit Barbeau, a professor in the biological science department at the Université du Québec à Montréal, and Dr. Marc Romney from St. Paul’s Hospital in B.C.
You need a “certain amount of virus” in order to test positive for it, Barbeau explained.
“But if you dilute it tenfold, then there’s a possibility that in that pool sample you’ll end up having a false negative,” he said.
“The more you pool, the more the sensitivity of the test is compromised,” Romney said. Another disadvantage is that it’s “labour intensive,” he added.
Still, Barbeau said it’s a strategy to consider in Canada.
“I think that’s something the government should definitely consider and start doing,” Barbeau said.
Health Canada says pooling samples is used to “increase throughput and to conserve laboratory supplies.”
“The challenge is to ensure that results are still accurate (i.e., specific and sensitive),” the department said in an email.
“Before sample pooling is implemented, laboratory professionals must conduct research studies to confirm accurate results.”
Furness sees pool testing as a way of protecting people who are at high daily risk of infection, like taxi drivers and retail workers.
“Even before we get to schools, we need to be able to think about testing that population, and that’s going to go way past our testing capacity. I’ve been very worried about that,” Furness said.
“If we add schools in in September, the only way we’re going to be able to safely able to send our kids to school is to test our teachers multiple times a week, and testing kids. Every school needs to be able to have constant, continuous testing. It’s the only way that we’re going to be able to do this.
“We just don’t have the capacity to do probably hundreds of thousands of tests a day in Ontario.”
The method was developed by the German Red Cross and Goethe University in Frankfurt.
They say they hope that it will increase testing capacity in Germany by a factor of 5 to 10. At the high end, that would bring Germany from about 40,000 tests a day to close to 400,000.
The German Red Cross’s Erhard Seifried if a pool was positive, the positive individual within it could be identified within four hours.
“If we want to do reopening, we need to really ramp up our testing,” Furness says. “I mean, really ramp it up. Ontario boasts a capacity of about 20,000 tests a day. That’s not even close to what we would need to do in order to really stay on top of the risk of reopening.”
Global News emailed federal and provincial health officials on whether pool testing is being used or considered in any way.
Health Canada said the National Microbiology Laboratory is working with provincial labs and “exploring the best way to increase testing capacity for COVID-19, especially in remote settings including Indigenous communities.”
At the moment, the national laboratory doesn’t pool samples for COVID-19 or any other infectious disease testing.
Lab scientists “are conducting research studies to verify if pooling laboratory specimens for point-of-care devices used in remote and clinical settings will provide accurate results, as there is a global shortage of laboratory supplies for these devices,” their email said.
Quebec, the hardest-hit province in Canada in terms of both COVID-19 caseload and death toll, said as of May 30, only two out of 48 laboratories — Trois-Rivières and Rimouski — were pooling samples.
When the pandemic began, there were several labs that pooled samples, but the majority of labs stopped the practice once the numbers of COVID-19 cases in Quebec increased, according to a statement.
Ontario, the province with the second highest number of cases and deaths, said it isn’t considering pool testing at the moment. British Columbia’s Centre for Disease Control said it is not currently doing pool testing.
Nova Scotia Health said it not considering it at the moment: “This technique is needed when the capacity of testing is exceeded. We have not yet exceeded our capacity for testing individual specimens but it is something we are aware of.”
Newfoundland and Labrador also said it isn’t currently considering pool testing.
As of May 15, Dr. Graham Tipples from Alberta Health Services said the province’s laboratories continue to look at all options.
“We are currently examining whether pooling would be an option to enhance capacity,” he said in a statement.
Tipples pointed out that pooling samples makes sense with a low positivity rate: “… if you have infrequent positives in the testing runs, then pooling can be an efficient way to do more with less.”
“However, if the positivity rate is slightly higher and you frequently need to re-run positive pools, then this approach is less appropriate.”
In Saskatchewan, the health ministry said they have validated a pool testing process in case they ever need to “conserve testing reagents” in the lab.
“However, at this time Saskatchewan has adequate testing capacity and we are not considering pooled testing for COVID-19,” their email said.
— With files from Reuters
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