The instructions for the rapid test kits are clear: the swab should be inserted into both nostrils. But to better detect the Omicron variant, wouldn’t it be better to take a sample from the throat, as some suggest on social networks? We discussed this with two experts.
• Read also: What to do if you test positive for COVID-19
• Read also: Here’s why the influencers at the party in Mexico were looking for petroleum jelly
Let’s start at the beginning: More and more people who take a rapid test insert a swab into their nose and mouth, rather than just the nose, and then share their results on social media.
In the last few weeks, the hashtag #SwabYourThroat (swab from your throat) has even emerged.
According to several accounts, the results obtained could change depending on whether the sample was taken from the nose or the throat.
Should we sample from the nose AND from the throat?
“Virologically speaking, the idea is not bad,” says Dr.D Judith Fafard, doctor specializing in microbiology-infectiology and medical director of the Laboratoire de santé publique du Québec (LSPQ), even if she cannot confirm the validity of this technique.
“It does not mean that the kit [de test rapide] does not allow the throat-nose sample, but it would be necessary to make sure of it “, she maintains, while recalling that it is better” to use the equipment according to the instructions of the manufacturer “.
“Before telling everyone ‘do that, it will work, it is reliable”, it would be necessary to verify that the test works correctly with this type of sample “, she continues.
• Read also: Quick tests: here’s why orange juice gives a positive result
How do you get the most accurate result possible?
Beyond the path the swab passes through, what matters most is the quality of the sample collected with the swab, says DD Fafard.
“Taking from the throat is not necessarily bad, but it is less sensitive [à la détection des protéines à la surface du virus qui cause la COVID-19] a nasopharyngeal swab [comme lors d’un test PCR]», She explains.
By getting the sample “as rich as possible”, that is to say by screening in the throat and deeper in the nose, it is however possible to “compensate for the loss of sensitivity”, she continues.
And how do you get the richest sample possible? By inserting the swab deeper into the nose than instructed, emphasizes Dr Donald Vinh, infectious disease specialist at the McGill University Health Center (MUHC).
Currently, instructions included in rapid test kits say rubbing the swab at the entrance to both nostrils, which worked well for other variants, he says. However, by going deeper into the nose, ie into the nasopharyngeal area, “we will probably have a better sample”.
“Testing ourselves is not always easy: sticking a stick in your nose and tickling your brain is not always easy,” he jokingly admits, while acknowledging that it can be more convenient to go by the gorge.
As to whether it is better to take from the throat and then from the nose or the opposite, again, it is “not as important as the quality of the sampling”, explains the MUHC infectious disease specialist.
What if we have two different results?
If you take a swab in the nose and another in the throat and one of the two results is positive, that suggests that you are contagious, insists the Dr Vinh. You will therefore have to follow the rules and put yourself in isolation.
Recall that Quebec has reduced the period of isolation for doubly vaccinated people from ten to five days.
• Read also: COVID-19: isolation period increases from 10 to 5 days, end of PCR tests
And if the result is negative despite the presence of certain symptoms, we must remain cautious and take the necessary precautions to reduce the risk of transmission, he adds. Rapid tests are indeed not as reliable as PCR tests, especially when it comes to the Omicron variant.
“Even if it’s negative, that doesn’t exclude the likelihood that the person is actually infected. It shouldn’t give a feeling of security. ”
Is there a greater risk of false positives through the throat?
The risks of having a false positive, that is to say a result which indicates that one is positive for COVID-19 when one is not really one, would also be higher when one carries out a test. swab in the throat, argue the two experts.
The presence of microbes in the secretions sampled from the throat could, for example, distort the results.
“We have seen false positives in the past, because we had different substances that had no effect on the membrane,” says DD Fafard.
But whether it is a false positive or a true positive result, it is necessary to isolate oneself, recalls the Dr Vinh.
• Read also: Your rapid test should be thrown in the trash, not for recycling
Why does Omicron affect the efficiency of the tests?
This variant, responsible for the explosion of COVID-19 cases observed in Quebec for a few weeks, would be able to reproduce 70 times faster through the respiratory tract, explains Dr Vinh. The numerous mutations of Omicron would also allow the virus to “stick differently” in the nasopharyngeal area and in the back of the throat.
“This is probably further proof that the Omicron variant is a different beast from other variants,” he says.
He also recalls that the rapid test kits provided to Quebecers were designed before the arrival of the Omicron variant.
Last week, the United States Medicines Agency (FDA) confirmed that rapid tests were less sensitive to this new variant. In other words: there is a greater chance that a test will show negative even if a person is infected.