Do you test covid-19, watch out for false positives!

Recently, president of Tanzania said covid-19 tests were phony, openly question official statistics on the number of cases reported. I invite you to see this article and this video where we learn that papaya tests positive for covid-19…

In parallel, Pr John Ioannidis, high-level epidemiologist, confirms tests are not as reliable as we might think. Here are his explanations, Minute 27.

I wanted to know more about the reliability of the tests by consulting the French review Prescribe and Swiss medical journal.

At the time of confinement, we are told about a massive testing policy: target 700,000 tests per week for symptomatic and contact cases of confirmed cases! "To avoid an accelerated spread of the virus, it will be necessary to break the chain of contamination. RT-PCR test, Covid-19 test, will be systematically applied as soon as a person is symptomatic of the disease " (see this article reporting the new measures from 11 May). If you are positive, you will be quarantined and the people you have met will be sought out and then invited to isolate yourself ! And if you don't have coronavirus after all? This is the angry question that I suggest you study today. Beyond the problem of medical confidentiality, this is a central point little mentioned by the media,

A PC test What?

You should first know that the majority of tests for coronavirus are "PCR" tests. It is a laboratory technique which allows the amplification of traces of RNA or DNA in order to see them in vitro.. It’s not the virus that is isolated, but fragments of sequences. This is a very complex laboratory technique, which is carried out in several stages with specific equipment. If you want to have an overview of the complexity I refer you to the description of Wikipedia.

Attention : improper handling or equipment and the result may be distorted. The test itself must also be high level of quality. As you'll discover, it's not systematically the case !

Numerous but ineffective tests!

Recently, I came across a journal web article Prescribe, intitulé: « Covid-19 : end of April 2020, the biological diagnostic tests are numerous, but often underperforming " (23 April 2020). The author writes : "The development of covid-19 diagnostic tests is abundant, under the pressure of the pandemic, and in practice the performance of the tests is still poorly evaluated, various, and often mediocre (…) Results are most often expressed qualitatively : presence or absence of virus. PCR tests were the only routine biological tests available until early April 2020. At the beginning of April 2020, antigenic tests are ineffective and have not been recommended by the World Health Organization (WHO) ».

To give you an idea of ​​the number of tests circulating on the market : " At 22 April 2020, 278 tests PCR, 149 tests rapid serology and 84 Elisa tests have been declared marketed in the world. We only have performance results for a few tests », writes the review Prescribe.

Sensitivity can be estimated between 56 and 83%

Comments confirmed by the Swiss medical journal, in its number published on 8 avril 2020: "Several studies have evaluated the properties of the nasopharyngeal smear-PCR in comparison with radiological examinations. The quality of sensitivity studies is low and the details of patient characteristics and the gold standard used are sparse ” (article: «Performance of the nasopharyngeal smear-PCR for the diagnosis of Covid-19. Practical recommendations based on the first scientific data»). "Based on the bibliographic data available, sensitivity can be estimated between 56 and 83% ". The least we can say is that it is not much! But that's not all.

And the specificity?

It's not just "sensitivity" that needs to be taken into account in test reliability, there is also "specificity", that is to say the ability of the test to properly target the virus sought and not another. What happens for example in case of attack by another virus? Couldn't these covid – 19 tests react positively in the presence of another corona virus, or that of the flu? We know that PCR tests can be distorted when the sample is contaminated with other strains, especially bacteria. (see this article published in 2007 in the Swiss Medical Journal). Cependant, I have not been able to find a source devoted to the reliability of the "specificity" of PCR or antigenic tests for covid-19 (I appeal to you if you have this information !).

Officially, everyone seems to agree that they are reliable to 99 % concerning the specificity. This is the percentage retained by the Swiss medical journal in its test reliability analysis. But she specifies that it is a bias necessary for these calculations. The majority of market tests probably do not have such a level of specificity as the review suggests Prescribe, even if this last note that many still have a specificity close to 100 %.

Are the French tests really reliable ?

In its specifications dated 16 April 2020, the High Health Authority (HAS) french, asked that the minimum performance of PCR and serological tests be "at 98 % for clinical specificity and to 90 % or 95 % according to the use of the test for clinical sensitivity ". But do these tests really exist on the market ? According to the review Prescribe, " At 17 April 2020, 38 PCR test kits were reimbursable by French Social Security, dont 9 validated by the National Reference Center (CNR) French (…) We do not know to what extent the validations by the French CNR, who has not communicated the performance of validated tests, meet these criteria ". I remind you of what we read in the Swiss medical journal : "Based on the bibliographic data available, sensitivity can be estimated between 56 and 83 % ».

More false positives than false negatives

Currently, the dominant theory tells us that with PCR tests, the risk comes mainly from false negatives, that is to say those who are falsely declared uncontaminated while they are carriers, asymptomatic or that they sometimes also have symptoms typical of covid. Autrement dit, the epidemic would be underestimated ... This is not really the opinion of the Swiss medical journal, "A single negative test can exclude a Covid-19 in most situations", she says, while emphasizing the caution of interpretation if there is a clinical picture: "A second test may be indicated".

When we look closely at the analysis made by the Swiss medical journal, we find that the positive results of PCR tests are less reliable than the negative results when they are practiced in a population which would count 10% contaminated or less.  But what does the incidence of the disease do in the population to determine the reliability of a test ? Obviously, scientists need to improve the interpretation of tests in a context where their reliability is not optimal. We are talking about " pretest probability ». "The interpretation of a test also depends on the frequency of the disease in the population group where the person is tested", confirms the review Prescribe.

The Swiss review tells us that the probability of really having the disease in the event of a positive result is 86-90% while probability of not having the disease, knowing that the test is negative is to 95-98%. I summarize, if you are not sick and you are tested with a PCR test, a negative result will be reliable to 95%. But if you have a positive result, it is only reliable when 86%. I remind you that the results of the review are based on a specificity optimal tests ie 99%…

What to think of mass screening ?

If mass screening is performed in a population affected by 10 % or less, there will probably be more false positives than false negatives. I give you the demonstration of the review Prescribe in his article "Predictive value of diagnostic test results : the example of the covid-19 tests ", which shows that the proportion of false positives can be dizzying.

"Assuming two serological tests for the Sars-CoV-2 virus, one of average performance with a sensitivity of 85% and a specificity of 98 %, and the other of poor performance, the sensitivity of which would be 65% and the specificity of 90%, we can calculate the probability that contact with the virus is properly diagnosed if we know the frequency of the disease.

 "The Institut Pasteur released the 20 April 2020 frequency estimates of Sars-CoV-2 infection in the general population in France at 11 May 2020. The proportion of people with antibodies is estimated at around 1,4% to 1,9% in Brittany, in New Aquitaine and Pays de la Loire, around 5% to 6% in Burgundy-Franche-Comté, in Corsica and the Hauts-de-France, and up to about 12% in the Grand-Est and in Île-de-France ».

" An example (among others) maybe that of a person with no notable symptoms from an area where 2 % residents have been infected with the Sars-CoV-2 virus which is being tested. If the test most successful is positive, the probability that the person tested was genuinely infected is from 45 % (positive predictive value, VPP). If the poor performance test is used and the result is positive, this probability is only 12 %. Autrement dit, the test is false positive in 83 % cases.

"Under the same test conditions but in a region where 12% residents have been infected, if the most successful test is positive, the probability that the person tested was genuinely infected is 85%. If the poor performance test is positive, that probability is only 47% ".

False positive but compulsory quarantine?

On the one hand, the quality of PCR tests on the market is decisive for the result, but on the other hand testing within the general population can also participate in generating a greater number of false positives. You have a 50% chance of ending up with a false test, which is like flipping a coin, or Russian roulette. Imagine you have a reliable test at 99 % : if we tested 10 million negative people in reality, this could potentially generate 100,000 false positive people[1]… Forcibly confined ? An epidemic of tests can lead to an epidemic of false contaminates and unnecessary confinements.

And the antigen tests?

Antigen tests are apparently no more reliable. Recently, we saw in the newspaper The Guardian du 26 April 2020,  le virologist Christian Drosten, initiator of the policy of massive tests in Germany (that he considers contaminated with 8%), deplore the fact that antigen tests are not reliable: "In Europe and the United States, all have false positives. "

According to the review Prescribe : "The detection of antibodies against this virus is mainly based on two types of tests, so-called serological : rapid diagnostic tests and Elisa-type tests (of enzyme-linked immunosorbent assay). Antibodies of the IgM and IgG type begin to be detectable in general 7 days after the start of infection. IgM remains detectable for 7 semaines. Mi-avril 2020, it is not known how long IgG remains detectable beyond 7 weeks ". Autrement dit, we may not yet be able to detect IgG well, which tell us both about your immune response and that it is an old condition.

Finally, other reason to invalidate the relevance of these tests is as follows : “No studies have shown that antiviral immunity is dependent on antibodies”, explains Emma Kahn, virologist, in an excellent article published on the Aimsib doctors association website (Covid-19 vaccine and group immunity, it's no ... and again no, the 3 May 2020).

“There is concern that the antigens selected for future ELISA serology tests (for the sensitivity and specificity conferred on these tests) be obsolete in a few weeks, explains the virologist. It is the same for the primers used in the Rt-PCR for the detection of the genetic material of the virus”…

The strange cases of "recontamination"

In my research, I came across a study of four cases in Wuhan, published in the journal  JAMA[2]. These patients were in quarantine and presented clinical signs with several positive PCR test results. Once recovered, they all tested negative twice in a row. At the end of their forties and before being "released", they were all tested again and there surprise: they were all positive again, without any return of symptoms.

This kind of study, like others who have seen this phenomenon on larger samples[3],  feeds the hypothesis of an absence of immunization against this virus. For my part, above all, it questions the reliability of tests in order to decide whether someone is carrying the virus or not.. Car, as one concludes chinese study published at the end of March in the Journal of medical virology[4] : "The results indicate that the RT - PCR test results of samples on pharyngeal swab were variable and potentially unstable, and they should not be considered as the only indicator for diagnosis, the treatment, isolation, recovery / discharge and transfer for hospitalized patients clinically diagnosed with COVID‐ 19 ”. This is what many countries are about to do.…

What is the number of “confirmed” cases worth ?

Asymptomatic and symptomatic people necessarily appear among the “confirmed” cases without having had covid-19. The percentage of the “contaminated” population is established partly on the basis of these same tests, sometimes even in the absence of clinical signs. But that these epidemiological data for covid-19 are really worth while, de toute évidence, reliability of tests is not acquired ?

An interesting article from Taiwan English News , published in March 2020, worried. The title : "In the middle of the viral panic, everyone ignores the problem of false positives and calls for more tests ". " Since a long time, PCR technique is known to create false positive results, even for established pathogens, well known and well studied. For example, false positive rate cited by United States Centers for Disease Control and Prevention as reason why PCR test should not be used on asymptomatic pertussis patients (whooping cough). »

Today, it's about only testing people symptomatic. But do we really have the certainty and the necessary hindsight to be sure that another viral or bacterial infection is not going to distort the test result ?

Stay skeptical of the result!

Dans tous les cas, given the current low level of bibliographic data on these tests, whether you test negative or positive, even being symptomatic, the laboratory result should not be taken as diagnostic certainty… Ask about the type of test used (serology, RT-PCR…). In case of a positive result, a second or even a third test is required, so as not to be unnecessarily or inappropriately medicated / confined. You can also request to be tested for other infectious agents to make sure there is no co-infection (absence of other human coronaviruses, flu virus, de rhinovirus, enterovirus, virus respiratoire syncytial, parainfluenza, metapneumovirus, adenovirus, bocavirus) to try to refine the diagnosis with the help of your doctor.

This article was produced for the Pure Health network, of the Health Nature Innovation group. To follow my next articles, you can join the network.

Read also :

And :

[1] See this article in English by David Crowe, big slayer of PCR tests for HIV.

[2] « Positive RT-PCR Test Results in Patients Recovered From COVID-19 », Lan Lan et al. Jama, 27 February 2020.

[3] Read also this article from Le Monde, « Covid-19 : questions about virus excretion and antibody response ", the 17 April 2020.

Feng E et al. Some Recovered Coronavirus Patients In Wuhan Are Testing Positive Again. NPR Goats and Soda. 2020 Mar 27.

[4] Read Y et in the. Stability issues of RT-PCR testing of SARS-CoV-2 for hospitalized patients clinically diagnosed with COVID-19. J Med Virol. 2020 Mar 26.

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3 Comment “Do you test covid-19, watch out for false positives!”

  1. capitale_info says:

    Excellent article. Vous avez très bien cerné les enjeux du testing COVID.
    Malheureusement les autorités de nombreux pays, pour des raisons diverses, ne tiennent absolument pas compte de tout celahors, en cette période de prévalence quasi-nulle (je parle pour la France car je connais parfaitement le contexte), les résultats des tests s’apparentent à ceux d’une roulette russe !

  2. GEREZ says:

    Good Morning,

    A question is bothering me. I understood well, from various sources, that tests were contaminated. Hence false positives. I also found out that cattle were vaccinated through the nose, performed like PCR tests. The current wave (25 oct 2020) could it be caused by contamination via these contaminated tests, so many people having been tested lately? With a slight modification of the virus, slightly different genome, mutation, to allow this second wave despite the collective immunity which should currently work against the covid of the spring? Who could answer this question? If the answer is yes, it is obvious that it is very serious, and I will be able to understand that I do not see her anywhere put; Yet, as far as I'm concerned, she arises, and greatly. Thank you for your reply, if you have one.
    Claudine Manage

  3. Priscilla Ducoeurjoly says:

    Your questions are legitimate, but nothing can prove such a hypothesis. Personally, I don't think that's possible at all. In addition there are too few contaminated tests (non sterile) to generate such a problem.

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