Wednesday, January 26, 2022

Nose or Throat? Use rapid test swabs as directed, say experts


Melissa Couto Zuber, The Canadian Press

Published on Wednesday, January 12, 2022 at 6:10 pm EST

Recent social media posts have corroborated the notion that swabbing the throat with a COVID-19 rapid antigen test kit may yield more accurate results against the omicron variant than testing for the virus in the nostrils.

But many experts are raising concerns with that approach, warning that detracting from the device’s intended use could lead to inaccurate results.

Earl Brown, a professor of microbiology and immunology at the University of Ottawa, says that even though omicrons may be more detectable in some people’s throats, the rapid test should be used as directed.

“These tests are developed and certified as nose tests – they are medical devices,” Brown said.

“You can’t just say through a press release or something that the test will be used differently now. There’s no approval for that.”

Brown said tests that change their direction will have to be re-verified by manufacturers and get approval from governing bodies.

Still, Brown cautioned, if the nasal sample is diluted, or if food or drink particles become mixed with saliva, then swelling of the throat could potentially alter the effectiveness of the test.

He said teens on TikTok have shown false positives when they mix soda with samples, mess with its pH, and skew the results.

While saliva tests for certain pathogens exist, including some COVID-19 rapid tests, Brown said they usually include instructions not to eat or drink anything for some time before taking them.

“With the nose, we know the chemistry, it doesn’t change much,” Brown said. “But with a saliva sample, you’ve got all the problems with eating and drinking, maybe smoking, all that changes the chemistry.”

Health Canada said in an emailed statement on Monday that medical equipment, including a supply of COVID-19 rapid tests, has been approved for use “as recommended by the manufacturer” in the country.

The agency’s guidance is to “use (tests) as directed”, but states that provinces and territories are able to offer their own guidance “outside the scope of the product’s label”.

However, the recommendations of several jurisdictions mirrored those of the national body till Tuesday.

The Nova Scotia Health Authority said self-administered rapid tests in the province are designed for nasal sampling, advising people to “correctly follow given instructions.” The organization said their position will continue “unless we receive a direction from the test manufacturer to replace the collection with Health Canada or by any other means supported by the data.”

Manitoba urged people to follow the instructions on its tests, noting on its website that different types may have different instructions. The province has warned that not following instructions “not waiting long enough or waiting too long to read test results” could lead to misdiagnosis.

Meanwhile, Alberta’s health website includes an instructional video from Rapid Response on how to use their specific nasal-swab tests. The video shows the swab used in both nostrils, with no mention of sore throat.

However, other countries have rapid tests that are for use in both the nose and throat.

A video from Public Health England demonstrates how to use a specific test where a “combined sample” is required. The results are to be sent to a laboratory for analysis.

While experts say that omicrons can be more detectable in some people’s throats, others will find higher concentrations of the virus in their noses. And some may not have high enough levels to be detected by rapid testing.

Eric Arts, an immunology professor at Western University and a researcher in viral control, said in an email that “there is no specific formula” to determine the optimal swab location, adding that a positive result is likely to be accurate, A negative does not mean the person is free from COVID-19.

He said many people get negative results on rapid tests before testing positive days later.

“If you have cold-like symptoms now, you should assume that you are infected with Omicron and confirm by getting tested every day or two,” Art said.

“Basically, a positive rapid test … is only positive if you have high levels of omicron replication, which unfortunately can take several days to develop and then be detected.”

The US-based CDC states on its website that the accuracy of rapid tests “depends largely on the circumstances in which they are used,” adding that they work best if the people they test are viral. load is highest.

The CDC says their tests are currently authorized for nasal use.

Cynthia Carr, an epidemiologist in Winnipeg, said if the virus is changing so that high concentrations are found in the throat, new tests should be authorized with instructions for that area.

But collecting proper throat samples at home can be problematic, she said, noting that keeping the test in the throat for long periods of time or “distinguishing between the mouth, the back of the mouth, and the actual throat” can be difficult.

“So even though more viruses may be detected, if (you) … are doing it improperly, you can end up with more pointless tests with false negatives.”

This report by The Canadian Press was first published on January 12, 2022.

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