Claim that Portuguese court found COVID-19 PCR tests to be 97% inaccurate based on misinterpreted findings – Health Feedback

CLAIM

MSM Silent As Court Holds PCR Covid Tests 97% Inaccurate - Unfit for Purpose

DETAILS

Factually inaccurate: A Portuguese courts conclusion that PCR tests are 97% inaccurate is based on misinterpreted findings. The findings were related to how well PCR tests could measure contagiousness, but were misconstrued to mean that most positive PCR tests are inaccurate.

KEY TAKE AWAY

PCR tests work by detecting a virus genetic material in biological samples like blood or saliva. These tests are highly sensitive and specific. Trace amounts of viral genetic material, left behind after an initial infection is over, can still be detected by PCR tests even when the infected person is no longer contagious. While PCR tests are excellent at detecting current and recent infections, there can be uncertainty when it comes to using them to determine if a person is still contagious.

The articles appearance in May 2024 belies the fact that this claim dates back to November 2020. In fact, much of the article was lifted from a November 2020 op-ed published by RT (formerly Russia Today), a media outlet controlled by the Russian government and known to spread disinformation. Science Feedback debunked similar claims in 2020 and 2021 (see reviews here, here, and here).

The claim is based on a ruling by Lisbons Court of Appeals regarding a case for habeas corpus, brought by a group of four German holidaymakers. The Regional Health Authority for the Azores required the group to isolate and quarantine after one of them received a positive COVID-19 PCR test result. This took place in August 2020 and was in line with Portugals COVID-19 policies at that time.

The court ultimately ruled that the groups confinement was illegal and ordered the four to be released. This decision was based in part on the courts assessment of the reliability of PCR tests. According to a report by The Portugal News, the judges concluded that the probability of a person receiving a false positive [from a PCR test] is 97% or higher, citing the following statement from Jaafar at al. in a letter to the editor of the journal Clinical Infectious Diseases[1]:

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

The judges spelled out their interpretation of this statement in their decision. The decision was primarily published in Portuguese, but it provided an English translation for the judges understanding of the letter by Jaafar and colleagues:

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.

However, this is a misinterpretation of the scientists findings, as well explain below.

In brief, the letter by Jaafar and colleagues dealt with the question of how well positive PCR tests correlate with a persons contagiousness.

PCR tests are considered the gold standard for COVID-19 testing[2,3]. As such, they form the basis of public health responses like isolation and quarantine. On a broader scale, they can inform school and business closures, as well as travel restrictions.

However, one potential issueas this New York Times report highlightedis that while contagiousness is a reason for isolation, a positive PCR result in itself may not necessarily mean a person is contagious. PCR tests are highly sensitive, which means they can detect even trace amounts of viral genetic material. This material can remain in the body for some time after the initial infection has passed and a person is no longer contagious.

In short, this means that infected people who are no longer contagious may isolate themselves unnecessarily if they still test positive (see Figure 1 below for an illustration).

Figure 1 How viral load evolves as disease progresses, and the implications for the accuracy of diagnostic tests like PCR and antigen tests. Source: Puhach et al.[3]

PCR tests detect the presence of the virus by makingor in scientific parlance, amplifyingcopies of a small part of the virus genetic material. The number of times the genetic material needs to be amplified (amplification cycles) to reach the threshold for a positive result is called the cycle threshold (Ct) value. The Ct value depends on how much virus is present in a sample. The more virus, the fewer the amplification cycles needed to reach the threshold for a positive result (low Ct value).

For that reason, some scientists suggest that Ct values should also be considered when determining the need for isolation, rather than rely solely on a positive or negative result. A high viral load (low Ct value) indicates that a person is likely infectious and needs to isolate.

But this approach also comes with caveats: interpreting a low viral load (high Ct value) is more difficult. It might indicate that a person is recovering and is no longer infectious. But it could also mean a person is still in the early stages of infection and will shortly become infectious (see Figure 1 above for an illustration).

To address the question of how well Ct values from PCR tests indicate contagiousness, Jaafar and colleagues collected the Ct values of approximately 3,000 PCR tests and checked whether the same samples contained live virus by using viral cultures. Viral cultures involve growing the virus, hence they can detect live, replicating virus and therefore provide a proxy measure for contagiousness.

The researchers reported that positive PCR results with a Ct of 25 were associated with up to 70% of positive viral culture results. But when they looked at positive PCR results with a Ct value of 30, the proportion of positive viral culture results fell to 20%. At a Ct of 35, fewer than 3% of cultures were positive.

This finding, which was cited as part of the basis for the Lisbon court ruling and for Turners claim, doesnt mean that PCR tests are 97% inaccurate. What it means is that the smaller the amount of viral genetic material in a sample (and the higher the Ct), the smaller the chance that live virusa marker of contagiousnessis present.

It also doesnt mean that PCR tests have a 97% chance of producing false positives. A false-positive result occurs when the test is positive in the absence of viral genetic material. The letter, on the other hand, explored the issue of trace amounts of viral material that are detectable by PCR tests and is unrelated to the problem of false positives.

In this blog post, virologist Ian Mackay explained that A positive RT-PCR result doesnt prove that replicating (also called infectious or viable) virus is present. It proves that its genetic material the RNA is present. But since RNA breaks down easily, the presence of viral RNA in biological samples indicates that the source of that RNAthe virusis likely present in the body. Therefore, PCR tests can still serve as a surrogate indicator of the presence of the infectious virus.

While viral cultures are an alternative to PCR tests for detecting live virus, they are slower and more expensive, Mackay explained. Hence viral cultures arent as widely used as PCR tests for detecting COVID-19 cases.

Vasco Bareto, a principal investigator at the Chronic Diseases Research Center of the NOVA University Lisbon, told Portuguese daily Pblico that the judges interpreted the results from Jaafar et al. incorrectly. PCR tests have a specificity and sensitivity greater than 95%. That is, in the overwhelming majority of cases they detect the virus that causes Covid-19, he said.

In conclusion, a Portuguese courts conclusion that PCR tests are 97% inaccurate is based on misinterpreted findings. The letter by Jaafar and colleagues didnt report that PCR tests have a 97% chance of producing false-positive results. Instead, their findings suggest that positive PCR results at high Ct valuesindicating very little viral genetic materialmay be a sign that a person likely isnt contagious.

View original post here:

Claim that Portuguese court found COVID-19 PCR tests to be 97% inaccurate based on misinterpreted findings - Health Feedback