The PCR is a genetic test that can detect a section of COVID’s genetic sequence within the sample. It does this by amplifying the sample hundreds of thousands of times until it has reached a predetermined threshold or limit. After reaching its cycle threshold (CT), if it detects a genetic trace of the virus, it returns a positive. If not, the result is negative. Several scientific studies have placed great importance on the number of cycles it takes until the genetic sequence of the virus is identified. If the genetic sequence is found after more than 35 cycles, it does not mean the subject actually has COVID.  As reported in the New York Times, experts acknowledge that the test should be limited to a maximum of 30 - 35 cycles, since, it has been found that results from tests using more than 35 cycles are 97% false positive. Depending on the number of days after the start of infection, a positive result even at 20 cycles could mean the subject is not infectious. Anthony Fauci, as director of the NIH, also acknowledged that “you almost never can culture virus from a 37-threshold cycle”.
The cycle threshold is not uniform across all testing facilities, nor is this information usually made public. The CDC accepts positive results from tests that amplify up to 40 cycles. In Canada, most labs use CT of more than 35 cycles. Israel reportedly uses 37 cycles. As such, the number of actual COVID cases is unclear. Florida introduced a state mandate to disclose the CT value whenever the result is positive so that doctors and patients can make more informed decisions about isolation and treatments.
In January 2021 the WHO acknowledged that individuals with high CT positive PCR test results should be retested. In May the CDC gave new guidelines for testing vaccinated people, stating that only positive results with a CT value of 28 or less should be considered valid.
Health officials in Sweden determined that PCR testing “cannot distinguish between viruses capable of infecting cells and viruses that have been neutralized.” During the course of the pandemic, several courts have ruled that a positive PCR test result is not sufficient to obligate quarantine including courts in Portugal, Vienna, and the Netherlands.
In July 2021 the CDC issued a statement that by the end of the year it would be withdrawing its recommendation for the continued use of PCR tests.
See PCR test and cycles explained
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