TORONTO -- As the Omicron variant of COVID-19 spreads, provinces are continuing to roll out at-home rapid tests, which are designed to detect the virus from a nasal swab.
In an email statement to CTVNews.ca, Health Canada says medical devices like rapid test kits should only be used as directed by the manufacturer. The agency says provinces and territories have the ability to authorize health products for "off-label" use, but so far, no provincial or territorial public health authority is recommending throat swabs.
Ontario’s Ministry of Health has said that throat swabs are “appropriate” for some rapid antigen tests, provided they are combined with swabs of both nostrils.
There have been numerous anecdotal reports on social media of people getting a positive test from a throat swab after testing negative through a nasal swab. These anecdotes have been shared through TikTok videos with millions of views and amplified with a hashtag on Twitter.
The Israeli Health Ministry is recommending swabs for both the throat and the nostril, even if goes against what the manufacturer recommends. In the U.K., some tests distributed by the National Health Service instruct both a throat and a nose swab.
The U.S. Food and Drug Administration has warned against using throat swabs. The agency tweeted last Friday, "FACT: When it comes to at-home rapid antigen #COVID19 tests, those swabs are for your nose and not your throat."
The throat swabbing advice is based on some early research suggesting that the Omicron variant is more detectable in the throat. One study from South Africa posted online on Christmas Eve found that nasal swabs were the most accurate at detecting the Delta variant of the virus. But for Omicron, nasal swabs could only detect the virus 86 per cent of the time while saliva samples detected the virus 100 per cent of the time. The study is a pre-print, which means it has yet to undergo the peer review process.
Experts are also divided on the use of throat swabs. McGill University infectious diseases specialist Dr. Matthew Oughton points out the rapid at-home tests that are currently available in Canada have only been tested on the basis of nasal swabs and haven’t been evaluated with swabs from other sites.
"As they say in the military, 'you go to war with the army you have, not the army you want,'" he told CTVNews.ca in an email last week. "The (rapid at-home tests) we have are the ones that are being deployed and will be used. It is important to understand their best use and their fundamental limitations in order to interpret what they are telling us."
Oughton also notes that the rapid tests already have a higher chance of producing false positives compared to PCR tests.
"I would advise caution in relying on anecdotal reports when it comes to changing recommendations on testing."
However, University of Toronto epidemiologist Dr. Colin Furness believes health authorities should come up with clear instructions on how to use throat swabs for rapid at-home tests, given the evidence that Omicron is behaving differently.
"The tests are much less sensitive to front of nose. But there has been no public education about self-swabbing the throat," he told CTVNews.ca in an email last week. "It’s fairly urgent that this guidance be developed, if we are to continue to rely on rapid tests as a screening tool."
With files from CTVNews.ca's Christy Somos and Sonja Puzic.
