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Why are some COVID-19 tests false positives?

May 5, 2020 — 

In a story on CBC, medical microbiologist Dr. Philippe Legasse-Weins explains why some tests for COVID-19 turn out to be false positives, like the one case in Nunavut that turned out to be a mistake.

A researcher at St. Boniface Hospital Research Foundation and also an associate UM professor, he says four false positives have been recorded in the province to date, and were basically simple errors.

“It is in a way bad luck, and it’s a fact of just the number of samples that we’re having to process in these automated instruments,” he said.

Dr. Legasse-Weins explained that lab-built robotic testing machines extract pieces of hundreds of different samples  and that cross-contamination can occur.

Occasionally, when there is a very strong sample next to a negative one, the result can be a very weak positive. 

“Sometimes there’s a great deal of urgency to get these reports out, so the results will be sent out right away,” Dr. Legasse-Weins explained.

“The main message,” he said, “is these are very rare events.”

Read the entire CBC article here.

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