Swabs, rapid tests, CT scans and X-rays to diagnose SARS-CoV-2 infections; so many methods but different results. So what should we use and when?

Together with COVID-19, some new terms have entered Italian households for the first time – and which are being used improperly by non-professionals. Let’s start with the now-famous swabs.

Swab tests: require a minimum of two hours for results

First of all, we must clarify that the swab is only a sampling tool; it doesn’t analyze the sample and is similar to a cotton swab. It would therefore be more correct to say “swab test“. The swabs are produced by various companies throughout the world, and one of the most important is Copan, located in Brescia, Italy. The nasopharyngeal sample is taken via the swab, or the mucus that is located in the deep part of the throat and nasal cavities. In some cases, the sample can be taken directly from the patient’s sputum, but since one of the symptoms of COVID-19 is a dry cough, it’s logically difficult for phlegm to be found.

The procedure continues by enclosing the swab in a special case that contains a liquid that preserves the sample, and then transporting the swab to the laboratory, in order to perform the actual testing.

The person in charge of the analysis, generally a Biologist or a specialized laboratory technician, must first extract the viral molecule which is called RNA (Ribonucleic Acid) which belongs to the virus — then he or she performs the test by using a special (and certified) kit. Once the RNA has been isolated, we move on to the next phase which consists of identifying the presence of SARS-CoV-2 which is responsible for the COVID-19 infection. Yes, because similar symptoms could be due to the traditional flu virus, and we need to be able to exclude this. This portion of the final analysis is performed with a technique called quantitative PCR (qPCR) and performed on very specific instruments.

This entire procedure, from collection to outcome, can last at least two hours, but if the laboratory has to analyze many, many swabs every day, the wait can be much longer. From direct experience, all the reference laboratories in Italy (and also elsewhere) are equipping themselves with automated tools to speed up the procedure and provide answers within the shortest time possible.

Rapid testing… is quick but is not very reliable

These are tests that are based on taking a droplet of blood and analyzing the antibodies that our immune system produces in response to an infection. They can also be performed in a pharmacy and provide an answer within a few minutes; a bit like a pregnancy test (i.e. either a positive or negative answer), but nothing more.

However, there are several concerns about these tests, as stated in a press release by Federfarma that advises against their use, since the identification of IgG and IgM antibodies (Type G and Type M immunoglobulins) directed toward the SARS-CoV-2 virus. These tests are not able to provide sufficiently reliable results, and cannot therefore replace the molecular test for the detection of the virus.

CT and X-Rays are only partially useful

CT scans and x-rays can detect the presence of pneumonia but CANNOT distinguish between COVID-19 pneumonia or pneumonia caused by other viruses or agents such as chlamydia or mycoplasma — because there is no difference in lung outcomes. Therefore, performing a CT scan would only provide false assurances to the patient, since the result could be negative for CT, but also result in the virus being circulated further and therefore increase infections.

For now, it’s best to avoid these sought-after “swab tests”

Many people wonder why we shouldn’t be using rapid swab tests because of their speed and ease of use. The reasons are as follows:

  • Rapid tests do NOT provide a conclusion as to the presence of the virus, as they only detect the presence of antibodies produced by our immune system in response to the SARS-CoV-2 infection.
  • Rapid tests CANNOT tell if the person is infected.
  • If the person is negative for the rapid test (i.e. he or she has not developed antibodies against the infection), it’s not proven that he or she is not infectious (because the incubation time of the virus is also 14 days, during this period our body does not produce antibodies), so we would be faced with so-called false negatives.
  • The rapid tests currently available on the market are NOT 100% reliable.

In conclusion

The only reliable tests for the identification of the virus in humans are swab tests that can detect the presence of SARS-CoV-2 shortly after infection.

The tests can only be performed by laboratories accredited by the respective National Health Service and indicated only by medical personnel.

If the positive patient has no additional symptoms, he or she must be swabbed twice within two days, in order to rule out a false negative before he or she can be defined as non-contagious.

This post is also available in: Italiano

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I've always been passionate about science and have a Degree in Biological Sciences and a PhD in Molecular and Cellular Biology. After six years of basic and applied research, I joined the company that provided the DNA sequencers that led Celera Genomics to complete the sequencing of the first human genome shortly before the same result was achieved by the "Human Genome Project" international public consortium. Subsequently, I became interested in human and animal diagnostics, and the development of molecular techniques from research-to-clinic. Science4Life represents the next stage of my personal journey, a stage in which I will make my experience and knowledge accessible to everyone.

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