With some experts expressing concern that Canada has inadequate resources to continue COVID-19 testing at the current rate, several provinces are exploring a new method that could allow labs to analyze more samples using fewer resources.
Known as pooled testing, the process works by combining a number of samples from different people and testing the combined sample. If the sample tests positive, then members of that group are each tested individually to determine who has the virus. The size of the group could range from five to 50, depending on the type of test used.
Pooled testing has been used in China, Germany and other countries to test large numbers of asymptomatic people, and studies show it can help to monitor viral spread in specific settings, such as schools. By running a single diagnostic test for a group of samples that are likely to be negative, public-health units can save time, testing materials and money.
The pooled testing method has also been used globally to test for diseases such as syphilis, HIV and Zika virus.
Alberta, Ontario, and British Columbia are among the provinces that have been exploring this testing option. In Edmonton, Alberta Precision Labs has been piloting pooled testing with groups of asymptomatic patients since mid-August.
“Pooling samples is an effective approach for performing a large number of tests while using less laboratory supplies and staff,” said a statement from Alberta Health Services (AHS), which oversees medical care in the province.
If the program is a success, they hope to be able to increase swabbing and testing capacity by 2.5 to three times, and supply faster turnaround times for results.
The aim to increase testing capacity comes as Alberta’s Chief Public Health Officer recommended teachers and school staff who are asymptomatic get tested, both before starting school and regularly during the year.
B.C. and Ontario are also considering pooled testing. Ontario Health has confirmed that several labs, including laboratories within the provinces’s COVID-19 Diagnostics Network, are currently validating this type of testing, and examining in which scenarios it could be used.
In B.C., the potential of a diminishing supply of testing material was a major factor in the decision to use pooled tests.
“B.C. will consider using batched or pooled testing if there is a point in time when the supply of reagents used for testing is at a level where conserving this supply is warranted,” said Libby Brown, spokesperson for the Provincial Health Services Authority.
Pooled testing has the same level of accuracy as individual tests, said Dr. Colin Furness, an infection control epidemiologist and assistant professor at the University of Toronto.
“It’s not that you have less chance of detecting the virus, because the sensitivity is the same,” he said. “And if they’re all negative, boom, you’ve done eight for the price of one.”
However, pooled testing is less effective in areas that have higher levels of infection within the population, he said, because a higher number of positive pool tests means that more people would have to be retested.
Dr. Furness said that public-health officials should nonetheless encourage asymptomatic people to get tested individually, whether or not pooled testing is available. Testing should be made more accessible to everyone as soon as possible, he added.
“This is an asymptomatic pandemic,” he said. ”You can have someone who feels super, and they can cause a lot of death in their wake. And that’s why we need very widespread testing, full stop.”
Other experts say that there are limits to how effective pooled testing can be.
Dr. Isaac Bogoch, an infectious-diseases specialist at Toronto General Hospital, said that a test can only give you information on a brief snapshot of time, because if a person was infected on the day of the test, it likely will not show up. Continuous testing of people in schools and in long-term care centres, for example, would be needed to ensure the virus doesn’t spread, he said.
Dr. Bogoch added that while he was in favour of implementing pooled testing, he did not recommend widespread asymptomatic testing with the currently used individual swab test. Since it involves discomfort as well as time and resources, he said it just isn’t a realistic option for people to get tested regularly.
The Public Health Agency of Canada’s nationwide data show that testing is on rise, while positive test rates are slowing down. From August 9 to 15, more than 48,000 people were tested a day, nearly 6,000 more a day than the average number of daily tests from the week before. Meanwhile, 0.8 per cent of tests were positive, down from to 0.9 per cent the week before.
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