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How pooling samples could impact COVID-19 testing in Alberta

Alberta Health Services is piloting a new way to test COVID-19 samples, by pooling together four samples taken from asymptomatic Albertans into a single specimen. As Julia Wong explains, it could allow labs to increase their capacity.

Alberta Health Services is piloting a new way to test COVID-19 samples: pool testing.

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The pilot, which is targeted towards samples taken from asymptomatic Albertans, would see four samples pooled together when tested. It is currently only being tried in Edmonton.

READ MORE: Hinshaw urges Alberta teachers to get tested for COVID-19 ahead of school reopenings

The pilot comes as school staff are being asked to get asymptomatic tests before they return to school and as the province continues to ramp up testing capacity, which had, at one point, been promised to hit 20,000 tests a day.

Total daily test numbers currently hover around 7,000 to 10,000 tests a day.

In pool testing, samples from four COVID-19 swabs are combined into a single specimen.

If the test comes back negative, then all four samples are marked negative; if the test comes back positive, the four samples are then individually tested.

“It does allow a lab to increase their capacity without necessarily increasing the number of supplies and people they would need to do that same testing,” said Nathan Zelyas, medical microbiologist and program lead for respiratory virus testing at Alberta Precision Labs.

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Read more: Alberta expands testing to anyone with COVID-19 symptoms

Zelyas said the pooling process is still being refined in the pilot and at this time, it’s hard to say what impact pool testing may have on timelines for testing and test results.

“I actually wouldn’t expect it at least to improve those turnaround times immediately but the more we streamline the process and the more we work out the kinks, I would expect, hopefully, to see a reduction over time,” he said.

David Evans, a virologist and professor in the Department of Medical Microbiology and Immunology at the University of Alberta, said pool testing can be effective to a certain extent — adding it works best if the positivity rate is low.

READ MORE: U.S. FDA approves pool testing for coronavirus as cases surge

“If you start to have a situation where a significant fraction of the specimens are contaminated, you get no advantage from this methods because odds are, you’ll start getting more and more positives, which you then have to go back and re-check anyway,” he said.

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“Once that [positivity rate] starts to climb then the advantages of the method start to disappear.”

Pool testing can, however, be advantageous when it comes to conserving lab supplies, according to Dr. Marc Romney, medical director of medical microbiology and virology at St. Paul’s Hospital in Vancouver.

“The labour has very finite resources,” he said.

“There are many components — one of them is reagents — beyond the reagents for a particular test. There’s also the other consumables related to that testing. For example, test tubes, pipet tips, there may be a shortage of pipet tips.”

Nevertheless, Romney said testing itself is complex and pooling increases the level of complexity and with it, human error.

“Whenever you are doing more manual work, it increases the chance the technologists will make a mistake. For example, you could have a positive pool and you resolve the pool and everything is negative. So what do you do? You’re stuck,” he said.

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“It could be contamination… it could be machine error, it could be a pipetting error. The more steps you include in a procedure, the more manual it becomes, the riskier the whole process.”

Zelyas agreed there are concerns about human error and said the process in Alberta is being automated as much as possible.

“Instead of having people pipetting and doing the pooling themselves, we have programmed an instrument to do that pooling for us,” he said.

“It’s not so much people needed to do the pooling and run the testing. We probably need more people, as much as possible, to do a lot of the data entry with thousands of samples coming in.”

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Some countries, such as Germany, have been using pool testing for some time. Zelyas said the lab wanted to make sure various processes were in place before taking on this testing method.

The pilot began Aug. 14. Zelyas said it may be a few weeks before the pilot can be determined to be a success and whether it can be expanded to other parts of the province.


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