[FALSE] Does the false positive rate of PCR-based nucleic acid testing for COVID-19 reach 97%?

 

Screenshot of the Facebook post.

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The Claim and Our Verdict

• The claim: A Facebook post published Feb. 7, 2022 claims that the false positive rate of PCR-based nucleic acid testing for COVID-19 can reach 97%.
• Fact-checking:
  • The claim quotes the speech of Kary Mullis, the inventor of the polymerase chain reaction (PCR) technique, during a talk about HIV testing using PCR. Mullis has passed away before the global outbreak of the coronavirus disease. He was not talking about COVID-19 testing. The claim quotes Mullis’s speech with false contextual information.
  • Studies have shown that the false positive rate of PCR testing for COVID-19 is low (1-2%). Yuen Kwok-yung, Chair professor of the department of microbiology, Li Ka Shing Faculty of Medicine of The University of Hong Kong, told HKBU Fact Check that the PCR technique remains by far the most reliable method for detecting COVID-19 infection.
  • PCR testing is recommended by the World Health Organization for screening for COVID-19, and this testing technique is widely used in the industry.
• Our ruling: We rate the claim as FALSE.

News Brief

A Facebook post published Feb. 7, 2022 claims that PCR is NOT a tool for virus detection, according to Kary Mullis, the inventor of PCR testing; The false positive rate of PCR tests can reach 97 %. Comments on the post showed that people regarded the “virus” in the post as “coronavirus.” Mullis is an American biochemist who invented the PCR technique.

As of the issuance of this report, the post had been shared 863 times, and had received 583 comments and 4,000 likes or reactions.

According to the Fact Sheet on the official website of the National Human Genome Research Institute, polymerase chain reaction (PCR) is a laboratory technique widely used in research and clinical practices to amplify or replicate small pieces of genetic material (i.e., DNA fragments). Mullis invented the PCR technique in 1985, for which he won the Nobel Prize in chemistry in 1993. PCR technique has been applied in various fields, including DNA fingerprinting, diagnosing genetic disorders, and detecting bacteria or viruses.

PCR has also been used for COVID-19 detection, specifically known as quantitative polymerase chain reaction (qPCR). This method detects whether a sample comes from an infected person by identifying, replicating and tagging the viral DNA.

A false positive result is that a test gives a positive result, but the coronavirus DNA is not present in the sample. On the contrary, a false negative result happens when the sample is from an infected person, but there is not enough viral genetic material in the sample for the viral DNA to be detected, which usually occurs early in the infection process. Overall, the probability of false negatives is much higher than that of false positives.

According to a study by Stanford University, PCR can also be used to detect HIV, but it is less used for that purpose due to the high cost of testing.

Fact-checking

 
1. Kary Mullis has not commented on the suitability of PCR for coronavirus testing
 
A keyword search found that the remarks of Mullis, as quoted in the claim, originate from an article published Dec. 9, 1996 by the American gay newspaper New York Native. The article was written by John Lauritsen.

The article quoted Mullis’ speech on the use of PCR for HIV testing. It makes no reference to COVID-19 testing.

According to the page introducing the winners on the official website of the Nobel Prize, Kary Mullis was born on Dec. 8, 1944 and passed away on Aug. 7, 2019. He was the winner of the 1993 Nobel Prize in chemistry. Relevant information showed that he supported “AIDS denialism” and believed that AIDS was not caused by HIV, which caused widespread controversy and criticism in academia. He passed away before the global outbreak of the coronavirus pandemic.

Kary Mullis has not made any remarks about the use of PCR for COVID-19 detection.
 
 
2. False positive rate of PCR testing for COVID-19
 
Studies have shown that the false positive rate of the PCR technique for COVID-19 detection is about 1-2%. Under normal medical practice and a clean laboratory environment, the false positive rate will not reach 97% as purported in the claim. Relevant data also shows that PCR is currently the most commonly used method for COVID-19 detection in the industry.

An article published Aug. 15, 2020, on the official website of College of American Pathologists, stated that taking account of the factors that may affect the test results, including sample collection, transportation and storage in actual operation, the clinical performance of PCR can reach 80% sensitivity and 98-99% specificity.

The relevant concepts are explained as follows:

• Sensitivity (also known as true positive rate): the ability of a test to correctly identify patients with a disease.
• Specificity (also known as true negative rate): the ability of a test to correctly identify people without the disease.
• True positive: the person has the disease and the test is positive.
• True negative: the person does not have the disease and the test is negative.
• False positive: the person does not have the disease and the test is positive.
• False negative: the person has the disease and the test is negative.
• Sensitivity (true positive rate) could be calculated with the following formula:
  Sensitivity = Number of true positives / (Number of true positive + Number of false negatives)
• Specificity (true negative rate) can be calculated with the following formula:
  Specificity = Number of true negatives / (Number of true negatives + Number of false positives)
• False positive rate (i.e., 100% – Specificity) can be calculated with the following formula:
  False positive rate = Number of false positives / (Number of true negatives + Number of false positives)

Therefore, the abovementioned study has proved that the false positive rate of PCR is 1-2%, far below 97% as purported in the claim.

This finding is corroborated by other studies. An article published Aug. 1, 2021, in the journal Am J Epidemiol, analyzed the accuracy of RT-PCR* testing. The test results showed that the sensitivity of RT-PCR testing was 68%, and the specificity was 99%. From this, it can be calculated that the false positive rate was about 1%.

*Note: Here and hereafter, the term “RT-PCR” refers to “reverse transcription polymerase chain reaction,” or “reverse transcription PCR,” which is a widely used variant of polymerase chain reaction (PCR).

PCR is recommended by the World Health Organization for coronavirus testing. According to an article published by the WHO, RT-PCR is currently the most common and accurate method for detecting COVID-19 infection. A video released Nov. 27, 2020 by the WHO also states that PCR is currently the most accurate and mature testing method for coronavirus detection.

Yuen Kwok-yung, Chair professor of the department of microbiology, Li Ka Shing Faculty of Medicine of The University of Hong Kong told HKBU Fact Check that RT-PCR remains by far the most reliable method for detecting COVID-19 infection.

RT-PCR is recognized by the Hong Kong SAR government for COVID-19 testing, as stated in its list of “Local COVID-19 RT-PCR testing institutions recognised by the Hong Kong SAR Government.”

The PCR technique for coronavirus detection used in laboratory tests can mostly obtain high specificity values, and the false positive rate is around 1-2%. No evidence has been found to support the claim that “the false positive rate of PCR-based nucleic acid testing for COVID-19 can reach 97%.”