A SCREENSHOT by a fringe Irish group claiming that PCR tests are “potentially up to 97% inaccurate” is years-old and, more importantly, false.

An Irish group modeled after the Yellow Vest protesters shared a screenshot earlier this week of an old article. 

“Mainstream Media Silent on Landmark Ruling Declaring PCR Test Unreliable for COVID-19”, a headline published on the website of Access to Justice for Families, a group to support people who want to navigate the English legal system “without traditional representation.” 

“In a groundbreaking legal decision,” it continues, “a Portuguese Court has declared COVID-19 PCR tests unreliable, potentially up to 97% inaccurate.”

The story is old — the Portuguese ruling mentioned in the headline was given in 2020. The story is so old, in fact, that The Journal has already debunked a version of it.

However, versions of the screenshot are still routinely posted. 

The Portuguese Court’s ruling does indeed say that a lone PCR test is “incapable of determining, beyond a reasonable doubt, that a positive result corresponds, in fact, to the infection of a person by the SARS-CoV-2 virus”.

However, an author of a letter published in an academic journal, which the ruling relied on for that judgement, told The Journal that the court had wrongly interpreted their work.

The Portuguese ruling came in November 2020 after German tourists asked to be released from mandatory quarantine in a hotel room imposed when one of them had tested positive for Covid-19 after falling ill.

The court heard that their mandatory isolation amounted to a detention and found that these should only be imposed by judicial authorities, not by the health authorities that had ordered the tourists to stay in their hotel.

However, part of that ruling also cast doubt on the ability of PCR tests to detect whether a person was infected with SARS-CoV-2, the virus that causes Covid-19, citing a letter about PCR cycles written by infectious disease scientist Bernard La Scola, among others, and published in the medical journal Clinical Infectious Diseases.

The research looked at how exactly PCRs work. The PCR (polymerase chain reaction) test is a way of multiplying pieces of genetic material from a tiny virus so that it becomes detectable. So, during each cycle while testing for COVID-19, any genetic material from SARS-CoV-2  is doubled.

PCR only works with DNA, so first viral RNA in the nasal swab is converted into DNA. Then the DNA is unzipped to give two single strands.

Scientists add special codes of DNA (primers) corresponding to the germ they are trying to detect. Only when there is a match can a special enzyme start doubling that DNA during each cycle.

If enough DNA is made, a signal is detected by the PCR machine and the PCR test is positive. If nothing is detected at that stage, the test result is that no virus is present. Most commercial test kits stop after 40 cycles.

“If a person has a positive PCR test at a cycle threshold of 35 or higher (as is the case in most laboratories in the USA and Europe), the chances of a person being infected are less than 3%,” the Portuguese ruling quotes the academic letter as saying. “The probability of the person receiving a false positive is 97% or higher.”

However, that quote does not appear in the paper.

“Of course PCR positive tests are not false positive in 97% of cases,” Dr Bernard La Scola, one of the letter’s authors told The Journal in 2020.

Instead, La Scola said that their research showed that if a PCR test detected SARS-CoV-2 below 35 cycles, it meant that the patient was likely to be contagious.

Above 35 cycles, a positive PCR test might indicate that the person had a small amount of the virus in their system. This could be because they were at the end or very early stages of an infection, but were not sick or infectious.

“It is a waste of time to consider these rare cases,” Dr La Scola said of such positive PCR results.

However, this did not mean that La Scola believed PCR tests were unreliable.

“Antigen tests have too many false negatives,” said Dr La Scola, referring to cases where people infected with the virus were wrongly given the all clear. “PCR is the best way to count cases.”

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