Social media users share screenshots claiming that the World Health Organization (WHO) disclosed guidance to laboratories and incorrectly stated that it reduces the positive number of results in the PCR (polymerase chain reaction) COVID-19 tests. The social media users claim that the WHO’s guidance amounts to the recognition that the current PCR tests have inflated the COVID-19 infection number. This statement is false. The WHO guidance was intended to remind laboratories to perform the tests with the prescribed instructions to ensure accuracy in the results.
Examples can be seen here, here, here and here.
Most reports contain a misleading tweet from Dr David Samadi which reads: ‘The World Health Organization has now announced guidance to laboratories around the world to reduce the cycle in PCR tests to get a more accurate version of COVID cases . The current cycle was far too high and resulted in any particle being a positive case. ‘The tweet no longer exists on Samadi’s Twitter page (twitter.com/drdavidsamadi).
Some posts here and here show a notice released by the WHO, visible here, published on 14 January 2021 and reissued on 20 January 2021 with clear language.
The WHO notice does not recommend laboratories to reduce the cycle in PCR tests. It recommends professional laboratories to use tests with the right instructions to ensure accurate results.
When contacted by email, the WHO told Reuters that it did not say that the PCR tests for COVID-19 were incorrect and that their guidance had been taken out of context. “Since the beginning of 2020, WHO has received ten reports of problems related to PCR tests for the detection of SARS-CoV-2 (the virus that causes COVID-19), including some products listed by WHO for emergency use, said the organization. said. “The reports were for misdiagnosis, both false positive and false negative results.”
The WHO confirmed after investigation that the tests were not used in accordance with the instructions provided by the manufacturers. Laboratories experienced problems when they did not apply the recommended ‘positivity threshold’, which can lead to false negative or false positive results.
Ian M. Mackay, a virologist and deputy professor at the University of Queensland in Australia, told Reuters in an email that the WHO notice was intended for professionals in the laboratory, especially those unfamiliar with the performing PCR tests in a pathology laboratory, and not the general. public.
“If a laboratory uses a commercial RT-PCR kit, they must follow the manufacturer’s instructions,” Mackay said.
In response to the statement in Samadi’s tweet that “the current cycle was far too high and led to any particle being declared a positive case”, Mackay said: “Apart from being completely wrong, this remark serves as an excellent indication of a person without an understanding of PCR, the design of PCR tests or the widespread use of PCR processes to test human samples in a quality pathology laboratory. He calls the remark ‘bizarre’ and mocks how opponents of the PCR tests use it.
PCR stands for Polymerase Chain Reaction, a process used to amplify DNA, and is performed a certain number of times to detect a virus. Mackay discusses the process in detail here , which explains that laboratory professionals can do 40 to 50 cycles of PCR to detect an otherwise small amount of viral DNA, which may vary by laboratory and test kit.
Mackay explained that reducing the cycle score will change almost nothing, a large majority of the results will remain positive and those tested for the virus will still be counted as cases.
“This is because most PCR results do not drop more than 40 cycles – the usual end point of a real-time PCR,” Mackay said. “They fall on a much earlier cycle number.” (This is explained in more detail here ).
The threshold cycle refers to a specific point in the test where the positive result occurs, Mackay explained. At that point, the fluorescence signal of the PCR test crosses a certain threshold, which can be determined by the user or the manufacturer of the test. The user can determine or adjust the value. ‘did the previous work to determine the best value for the threshold,’ ‘Mackay said.
Harvard Health explains on its website here that PCR tests are very accurate, with most false-positive results due to errors in performing the test.
This claim was also settled by Factcheck.org (here) and scientific fact-checkers Health Feedback (here).
Samadi did not immediately respond to Reuters’ request to comment on the misinformation due to his tweet which has now been removed.
VERDICT
Untrue. WHO has not released any clues that say that PCR tests for COVID-19 resulted in inflated positive results, but rather tried to address accuracy issues as PCR tests were not performed correctly.
This article was produced by the Reuters Fact Check team. Read more about our fact-checking work here.