It's not the real thing: Youth trick COVID-19 tests using cola

MONTREAL -

A few drops of fruit juice or soft drink can apparently be enough to produce a false-positive result in a COVID-19 test, according to videos that have been circulating online for several months.

Lateral flow tests, or chromatographic tests, work much like pregnancy tests and are much more common in Europe than in Canada. These are the tests, for example, that have been sent to British households for home testing.

Some young people have discovered that all they have to do is pour a few drops of cola or juice onto the strip and the two little lines that indicate that they are carrying the virus will appear (which can then earn them a few days off from school).

"I find this very interesting considering that some countries were trying to use saliva directly for lateral flow testing," said CHU Sainte-Justine Dr. Caroline Quach-Thanh. "But in Canada, the (lateral flow test) that has been authorized is only the nasal swab test. So the risk of there being Coke in there is much less likely."

A screening test that uses saliva deposited on a strip has been approved in the U.S., but the company has reportedly not applied for approval in Canada, she added.

The process by which drops of juice or cola fool the test is so complex that only experts would likely be able to understand the details.

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That said, when the test is working properly, the antibodies to COVID-19 in the test detect the presence of the virus in saliva, causing the two red lines to appear. However, it appears that the acidity of the drink mimics these antibodies, which will erroneously indicate a positive result.

In other words, because the antibodies have been altered by the acidity of the drink, the test concludes that SARS-CoV-2 is present when it is not.

"It's a very reliable test. There are more false negatives than false positives with this test," said Quach. "But it does make you think about what can cause false positives on these tests."

As for the risk of young people taking advantage of the situation to avoid a math test that has been giving them cold sweats for the past few days (when they go back to school), it should be noted that home testing is much less widespread in Canada than in Europe.

In Canada, testing is more often than not done in the presence of another person who records the results. A situation like the one seen in Europe would therefore be unlikely to occur.

"And even if it were possible, I still have faith in our youth," said Quach. "I think the kids are so sick of being at home and not seeing their friends. I think they want to go to school."

-- this report by The Canadian Press was first published in French on July 11, 2021.