Health
Online posting distorts WHO’s COVID-19 PCR test guidelines
Claim: WHO has changed the COVID-19 inspection guidelines. One PCR test is not enough to diagnose COVID-19
Since its worldwide appearance over a year ago, PCR tests (molecular tests that diagnose infections by detecting genetic material) have been used to distinguish COVID-19 positives from negatives. However, according to one Facebook post, the PCR test may not be fully confirmed.
“Does anyone catch the WHO website? Yesterday, on the day of its inception, the PCR test recommendations changed,” wrote Facebook user Maria Dawn Tyler. In January. twenty one..
“Currently, a positive PCR test is not enough to confirm a positive case. It needs a clinical correlation with a second test. This means it is symptomatic, and to count it, symptoms Tell your doctor that you have Covid based on. As a positive case. “
Tyler further states that this does not mean that asymptomatic individuals (individuals who do not show or have not experienced coronavirus symptoms) are not considered positive cases, nor do those who have undergone only one test. Insist.
“Therefore, the hundreds of thousands of cases that are now suddenly documented are not really positive and are no longer counted. It’s amazing how few they are now,” she concludes. ..
It is echoing that a single positive COVID-19 PCR test is no longer counted in new cases Elsewhere on social media..Some posts also quote deleted ones January 21 Tweet Newsmax contributor and urologist Dr. David Samadi World Health Organization Information Notification..
“The World Health Organization has now released guidance to laboratories around the world to reduce the number of PCR test cycles to get a more accurate representation of COVID cases,” wrote Samadi, “currently in use. The PCR cycle being done is too high, and as a result, every particle is declared a positive case. ”
USA TODAY asked Facebook users for further comments.
More:Fact Check: COVID-19 vaccine is unlikely to have been the cause of Hank Aaron’s death
PCR: Its origin and mechanism
PCR, or polymerase chain reaction, was devised by Biochemist Kary Mullis, Employees The now obsolete Cetus Corp.As an answer to the problems faced by scientists, in April 1983: How to quickly and mass-copy DNA, especially specific genes or sections?
To do that, Mullis took advantage of the amazing natural function of an enzyme called DNA polymerase. Discovered by biochemist Arthur Kornberg A colleague at Stanford University in the mid-1950s. DNA polymerase is like a miniature Xerox copier that could assemble DNA given the template strands and nucleotides that are the key components of DNA.
During PCR, DNA polymerase unfolds two strands separated from each other by heat with the help of a molecule called a DNA primer, which is a short gene sequence that binds to the site of interest that provides the replication origin of the enzyme. Copy the helical structure.
DNA rewinding and separation, DNA primer binding, and copying by DNA polymerase – alias Denaturation, annealing and elongation – Repeated an average of 40 times per cycle, producing a huge 100 billion copies of the retrieved DNA segment.
However, because the COVID-19 genome is made up of RNA, there is one prerequisite step. Another enzyme, called reverse transcriptase, is used to rewrite the genetic material into DNA. It is commonly used to convert RNA-based viruses such as hepatitis C and influenza A. Discoveries of the 1970s..
PCR test is very accurate, but false negatives and positives can occur
Its specificity and sensitivity make PCR a useful and widely used diagnostic tool, but misuse can lead to misdiagnosis. This is the main reason behind WHO information notifications.
“Since the beginning of 2020, WHO has received 10 reports of PCR test-related problems for the detection of SARS-CoV-2, some of which WHO has listed for emergency use. The product included. Reports were misdiagnosis, both false positives and negatives. Results. ” By email to Reuters..
WHO’s investigation into these reports revealed that the tests were not used properly according to the manufacturer’s instructions. The laboratory was particularly concerned about “if the recommended positive threshold was not applied” or the number of PCR cycles required to amplify enough DNA to confirm a positive signal.
“This can result in either false negative results (if the applied threshold is low) or false positives (if the threshold is high),” WHO explained. In a statement to FactCheck.org..
so January blog post Discuss WHO information notifications, Dr. Ian M. McKayA virologist and part-time associate professor at the University of Queensland, Australia, said the notice was “written for some of you, perhaps the first to perform high-throughput testing of human specimens.” It needs to take some time. ” What are you trying to achieve here? “
“If you use a commercially available RT-PCR kit in your lab, you must follow the manufacturer’s instructions, otherwise the results produced may not be the best and most accurate result the kit can provide.” Mackay emphasized to Reuters.
It’s worth noting that the PCR test is generally very accurate and the chances of false positives “should be close to zero.” Dr. Robert Schmerling In the article in August Describes the different types of COVID-19 tests at Harvard Health.
“Most false positive results are believed to be due to laboratory contamination or other problems with the laboratory’s testing methods, rather than the limitations of the test itself,” Schmerling said.
False negatives usually occur when a person is tested very early and the coronavirus is not replicated enough to detect it. The Washington Post reported..
Is it a problem with too many cycles?
Samadhi’s claim that the WHO information notification includes a change in the number of PCR cycles is not mentioned anywhere in the notification, “because the current cycle was too high and caused false positives.”
“I don’t know how it was misunderstood about changing the number of cycles used,” McKay said in the same blog post about Samadhi’s tweet.
“Most of the positives are indisputably positive,” he wrote, looking at the UK COVID-19 test data, even if the number of cycles was reduced by 10.
The number of cycles performed can be important for other reasons. This is to determine the degree of infection of a person infected with the coronavirus.
In September Science reported Some early studies have found that patients with early infections have a cycle threshold (CT) value of “less than 30, often less than 20, indicating high levels of virus.” .. How this works is because there is an inverse relationship between CT and viral load. The more viral genetic material a person has to start, the fewer PCR cycles are required to get a positive result.
Examining CT values ​​along with PCR results may help epidemiologists track outbreaks, he said. Dr. Michael MinaInterview with Science, an epidemiologist at TH Chan School of Public Health at Harvard University. It also helps healthcare professionals identify patients at risk of serious illness or death. One Brazilian study And Another from Weil Cornell Medicine Found.
However, including CT values ​​is not entirely clear. Dr. Matthew VinickerA professor of laboratory medicine and pathology at May York Clinic told FactCheck.org that he had a high PCR cycle value or a low positive PCR result to show that someone was no longer infected. And we haven’t reached the peak of infectivity yet. “
He also said, “The quality and type of sample can also affect the number of cycles required to detect a virus, so a high cycle result means that a person has only a small amount or debris of the virus. It doesn’t mean that you don’t have it. ”
WHO guidelines and asymptomatic people
A Facebook post claiming that asymptomatic individuals no longer count as positive cases is not mentioned anywhere in the WHO information notice.
Follow asymptomatic cases accounting for 59% of COVID-19 spreads According to a recent study, Proven to be difficult because many infections are not detected. Some studies Also, testing asymptomatic individuals with a standard nasopharyngeal or pharyngeal swab can result in false negative results, which in turn can lead to an undercount of COVID-19 cases in the United States. Also suggests.
No need for two tests
Neither is it suggested anywhere in the WHO notification that a single positive COVID-19 test will no longer be counted as a positive case.
Neither the Centers for Disease Control and Prevention nor WHO have published new case definitions since January 21st. The CDC COVID-19 case definition (suspicious, possible, or confirmed) is: April And August Both cite “confirmation laboratory evidence” as the only evidence needed to classify “confirmed” cases.
WHO changes, inauguration are not linked
The allegations linking WHO’s new guidance to President Joe Biden’s inauguration on January 20 also appear unfounded, as it is the second iteration of the information. First appearance on December 7, 2020..
Our decision: wrong
The claim that WHO has changed the COVID-19 inspection guidelines is false. The WHO information notice, first displayed on December 7, 2020, prompted laboratories to follow the manufacturer’s instructions to reduce inaccurate problems for a new period of COVID-19 PCR testing. The claim that WHO reduces the number of cycles, or the number of PCRs performed to amplify the DNA contained in a sample, is not mentioned anywhere in WHO’s information notice and is unfounded. Similarly, the claim that a single positive COVID-19 test is no longer counted as a positive case by itself. There is no evidence to suggest that asymptomatic individuals are no longer counted in COVID-19-positive cases. It also seems unfounded to associate the new recommendations with President Joe Biden’s inauguration.
Our Fact Check Source:
- World Health Organization, January 13, “Nucleic acid test (NAT) technology using polymerase chain reaction (PCR) to detect SARS-CoV-2“”
- Scientific American, Accessed February 3 “Abnormal origin of polymerase chain reaction“”
- The New York Times, July 23, 1991, “Two biotechnology pioneers to merge“”
- Journal of Biological Chemistry, December 9, 2005, “Discovery of DNA polymerase I by Arthur Kornberg“”
- Nature, accessed on February 4th “Scientists can make copies of genes through PCR“”
- Annual Review of Virology, September 29, 2016, “Discovery of reverse transcriptase“”
- Reuters, February 4, “Fact Check: WHO has released guidance on the proper use of tests. PCR tests did not show an increase in the number of infections“”
- FactCheck.org, January 29, “Virus posts distort WHO guidance on COVID-19 testing“”
- Virology Down Under, January 23, “WHO for new PCR users: Read the damn manual!“”
- Harvard Health, August 10, 2020, “Which is the best test for COVID-19?“”
- The Washington Post, January 14, “Three reasons why a negative coronavirus test does not necessarily mean that you are not infected“”
- Science, September 29, 2020, “One number helps determine the infectivity of COVID-19 patients.Must be included in test results?? “
- American Journal of Tropical Medicine and Hygiene, November 1, “Is the higher viral load of SARS-CoV-2 associated with death?“”
- Clinical Infectious Diseases, June 30, 2020, “Effect of Severe Acute Respiratory Syndrome Coronavirus 2 viral load on the risk of inoculation and death in hospitalized patients with coronavirus disease 2019“”
- JAMA Network, January. 7, “COVID-19 SARS-CoV-2 infection from asymptomatic individuals“”
- Nature Communications, September 9, 2020, “Significant underestimation of SARS-CoV-2 infection in the United States“”
- Centers for Disease Control and Prevention, April 5, 2020, “Coronavirus Disease 2019 (COVID-19) 2020 Provisional Case Definition, Approved April 5, 2020“”
- Centers for Disease Control and Prevention, April 5, 2020, “Coronavirus Disease 2019 (COVID-19) 2020 Provisional Case Definition, Approved August 5, 2020“”
- World Health Organization by Wayback Machine, December 7, 2020..
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Our fact checking work is partially supported by a grant from Facebook.
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