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WHO did not say PCR test flaw led to overstated COVID-19 cases

January 28, 2021 GMT

CLAIM: The World Health Organization admits that PCR tests to diagnose COVID-19 gave massive false positives, overinflating COVID-19 case numbers. 

AP’S ASSESSMENT: False. A WHO press release is being misrepresented online to say it shows that polymerase chain reaction (PCR) tests for COVID-19 caused large scale false positives. 

THE FACTS: Since the outset of the pandemic, some social media users have been falsely suggesting that false positive test results are the real reason behind the millions of reported COVID-19 cases. 

The latest posts are misrepresenting a WHO information notice to spread the false claim online. In widely shared posts on Facebook and Twitter, social media users are claiming that WHO admitted that PCR tests were causing false positives. Polymerase chain reaction test kits determine the genetic material of the virus in cycles and rely on specialty lab equipment and chemicals. The PCR test is generally a more sensitive test compared to rapid antigen tests, which identify proteins from the virus. 

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WHO first released an informational notice on Dec. 14 to update lab technicians to clarify instructions when analyzing PCR tests for COVID-19. WHO then updated the news release and published it on Jan. 20. The January release was then amplified online by accounts claiming it revealed WHO’s failure. 

“Wait. So there were too many false positives because the PCR tests were set at too high a threshold?” one Facebook post said. “Man, I hadn’t heard that anywhere —- except about 5 million times from reputable doctors who were conveniently silenced by the media for the past 10 months.”

But WHO did not make any admission nor did the health agency see a large scale number of false positives. The supposedly “massive” false positives being mentioned in the post were in fact much rarer. WHO told The Associated Press that it has received 10 reports of problems related to PCR tests for the detection of SARS-CoV-2. 

“The reports were for misdiagnosis, both false positive and false negative results,” according to WHO. “After thorough investigation, WHO confirmed that tests were not always being used appropriately and in accordance with the instructions provided by the manufacturer.”

The release emphasized the importance of knowing the details about the patient, the number of cycles of testing done when analyzing the specimen provided as well as the patient’s clinical history. 

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PCR tests work by analyzing the viral load in cycles. Dr. Wafaa El-Sadr, a professor of epidemiology and medicine at the Columbia University Mailman School of Public Health, said the higher the viral load in a patient the easier it is for a PCR test to become positive. More cycles of the test are needed to detect infections with a lower viral load, such as at the start or end of having the virus. 

“It’s not a problem with the PCR test,” she said. “It’s the nature of how tests perform and how common the condition is in the population you are testing.” 

According to WHO, lab professionals encountered problems with the tests “when they did not apply the recommended positivity threshold – this can result in either false negative results (if the threshold applied is lower) or false positives (if threshold is higher).”

“We know that very few PCR results are false positives and so they are absolutely not usually contributing to the number of positive test results that are called,” said Dr. Stanley H. Weiss, professor of medicine at the Rutgers New Jersey Medical School. 

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This is part of The Associated Press’ ongoing effort to fact-check misinformation that is shared widely online, including work with Facebook to identify and reduce the circulation of false stories on the platform.

 Here’s more information on Facebook’s fact-checking program: https://www.facebook.com/help/1952307158131536