A Closer Look at the PCR Test Method
Kary Banks Mullis (Dec 1944 - Aug 2019) an American biochemist, was the inventor of the polymerase chain reaction (PCR) technique. He shared the 1993 Nobel Prize in Chemistry with Michael Smith and was awarded the Japan Prize in the same year. His invention became a central technique in biochemistry and molecular biology, described by The New York Times as "highly original and significant, virtually dividing biology into the two epochs of before PCR and after PCR (Wikipedia).
Listen to what he said about the PCR method used for detection of virus in general.
A PCR test is amplifying samples through repetitive cycles. The lower the virus concentration in the sample, the more cycles are needed to achieve a positive result. Many US labs work with 35 to 45 cycles, while many European labs work with 30 to 40 cycles.
The research group of French professor Didier Raoult has recently shown that at a cycle threshold (ct) of 25, about 70% of samples remained positive in cell culture (i.e. were infectious); at a ct of 30, 20% of samples remained positive; at a ct of 35, 3% of samples remained positive; and at a ct above 35, no sample remained positive (infectious) in cell culture.
This means that if a person gets a "positive" PCR test result at a cycle threshold of 35 or higher (as applied in most US labs and many European labs), the chance that the person is infectious is less than 3%. The chance that the person received a "false positive" result is 97% or higher.
The issues with PCR tests are numerous:
- There can be large-scale test kit contamination, as both the US and the UK (and several African countries) discovered during the early phase of the pandemic.
- There can be testing site or lab contamination, which has led to countless false positive results, school closures, nursing home quarantines, canceled sports events, and more.
- The PCR test can react to other coronaviruses. According to lab examinations, this happens in about 1% to 3% of cases if only one target gene is tested, as is the case in many (but not all) labs and as the WHO itself has recommended to avoid ambiguous positive/negative test results.
- The PCR test can detect non-infectious virus fragments weeks after an active infection, or from an infection of a contact person, as the US CDC confirmed.
- The PCR test can detect viable virus in quantities too small to be infectious
Read : The Trouble With PCR Test