By Peter Bianco
On November 11, 2020, a Portuguese appeal court ruled it was unlawful to quarantine people based solely on a PCR test.
The court stated, the test’s reliability depends on the number of cycles used and the viral load present. Citing Jaafar et al. 2020, the court concludes that “if someone is tested by PCR as positive when a threshold of 35 cycles or higher is used (as is the rule in most laboratories in Europe and the US), the probability that said person is infected is less than 3%, and the probability that said result is a false positive is 97%.” The court further notes that the cycle threshold used for the PCR tests currently being made in Portugal is unknown.
This case concerned the fact that four people had been quarantined by the Regional Health Authority. Of these, one had tested positive for COVID using a PCR test; the other three were deemed to have undergone a high risk of exposure. Consequently, the Regional Health Authority decided that all four were infectious and a health hazard, which required that they go into isolation.
The court’s summary of the case to rule against the Regional Health Authority’s appeal reads as follows: “Given how much scientific doubt exists — as voiced by experts, i.e., those who matter — about the reliability of the PCR tests, given the lack of information concerning the tests’ analytical parameters, and in the absence of a physician’s diagnosis supporting the existence of infection or risk, there is no way this court would ever be able to determine whether C was indeed a carrier of the SARS-CoV-2 virus, or whether A, B and D had been at a high risk of exposure to it.”
In the US, the FDA’s instructions for PCR testing recommends a threshold of 40 cycles for a specimen to be considered positive. See page 35 of the instructions.
At 25 cycles the original material has been multiplied 33,554,432 times.
At 30 cycles the original material has been multiplied 1,073,741,824 times.
At 40 cycles the original material has been multiplied 1,099,511,627,776 times.
As you can see there is quite a difference in magnification at various cycle thresholds.
It is also important to remember PCR was invented as a way to create copies of genetic material. Its was never intended to be a diagnostic tool.