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#COVID19PTTHE TESTING

Summary of tests.

Introduction

Did the CDC issue an alert admitting that PCR tests do not distinguish between COVID-19 and Influenza (flu)? The simple answer is no, as you can see in the image and that you can consult in this link: Lab Alert: Changes to CDC RT-PCR for SARS-CoV-2 Testing.

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EXPLANATION

What a CDC says it suggests that laboratories should start using tests that can detect both the SARS-CoV-2 virus and the Influenza virus at the same time. And the key word here is “at the same time”.

RT-PCR tests for COVID-19 detect SARS-CoV-2 virus ONLY. How? Let's try to explain: 

  • An RT-PCR test is a test that searches for predefined genetic material. That is, the RT-PCR test can be used to search for any virus, any bacterium, any genetic material, etc. In theory, any organism that has a specific gene can be searched for by RT-PCR. The result will depend only on what the target gene is and whether that target gene is in the sample or not.
  • When you do an RT-PCR for COVID19, this test will compare the genetic material of the sample with known examples of COVID genetic material. 
  • In the case of SARS-CoV-2, the targets are parts of the genes encoding for nucleoprotein (N), shell (E), spicule (S), or ORF-1. These target genes have been chosen and sequenced so that they are similar between different variants and usually more than one is sought to consider a positive result.
  • RT-PCR tests to detect influenza, on the other hand, usually look for specific genetic material of Influenza and usually target the parts of the M genes (protein matrix), NP gene (non-structural protein of Influenza) and parts of the genes associated with the subtypes of Hemagglutinins (H) or Neuraminidases (A). It is these different tests and different targets that allow us to distinguish Influenza A from Influenza B and determine influenza subtypes. Do you remember H1N1, H5N1, etc? It is with the research of genes associated with Hemagglutinins and Neuraminidases specific to Influenza viruses that we can catalog them.

They seem to be different genes, don't they? It is not possible for a COVID test to be positive in the presence of influenza viruses or for an RT-PCR test for influenza to be positive only in the presence of COVID19: They are completely different viruses and completely different genes. Only the biochemical basis of the test is similar. 

The symptoms of Influenza and COVID are similar, yes. But... if it looks like a duck, walks like a duck, quacks like a duck, flies like a duck and *appears on RT-PCR like a duck*... maybe it's a duck. Quack.

The new tests proposed by the CDC look for 3 types of viruses (Influenza A, Influenza B and SARS-COV-2) at the same time. Why? Because we've known for a long time that the symptoms are similar, and with the lifting of restrictions, we're going to have several viruses circulating at the same time. It will be increasingly important to distinguish the prevalence of different viruses. 

MONITORING

Monitoring of subtypes and prevalence of circulating influenza (flu) strains is not new and has been coordinated for many years by INSA. http://www.insa.min-saude.pt/instituto-ricardo-jorge-reativa-programa-nacional-de-vigilancia-da-gripe-epoca-2020-21/.

NOT EVERYTHING IS GRIPE OR COVID

Finally, it is important to remember that not everything that is not COVID-19 is flu. In addition to SARS-CoV-2 and influenza, there are many other viruses and bacteria from several different families that still circulate and that can cause us symptoms more or less similar to COVID or influenza! Examples on the way? We'll save them all, one day we'll build a castle on a petri dish. Respiratory syncytial virus, mononucleosis (caused by the Epstein-Barr virus) or other bacterial infections may include some symptoms common to influenza or COVID19. 

As for the tweets out there that claim the CDC announced that new tests were needed to distinguish between flu and COVID-19, those tweets are fake. 

What is said by the CDC, is that testing for the 3 viruses at the same time (SARS-CoV-2/Influenza A/Influenza B) is advantageous because you can make the differential diagnosis and follow-up of the different diseases immediately.

“CDC has developed two laboratory tests that identify SARS-CoV-2, the virus that causes COVID-19. The newer of these tests also tests for influenza A and B viruses. Testing for all three viruses at the same time will provide public health officials with information they need to help reduce the spread of these viruses in the community while conserving resources that are in short supply.” Source: https://www.cdc.gov/coronavirus/2019-ncov/lab/testing.html.

For all this it is false that the PCR tests *for COVID-19* also detect the flu virus by mistake, and that is why there were not many cases of flu last winter. The COVID19* PCR test only detects SARS-COV-2 and the influenza* PCR test only detects Influenza.

GRIPE

The reduction in influenza cases was due to the use of masks, social distancing, confinement, and also to individual sanitary hygiene measures that were more present in our lives, as you can see here: https://www.scientificamerican.com/article/flu-has-disappeared-worldwide-during-the-covid-pandemic1/.

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