What is ATPG for automatic test package generation
Covid-19: How do the new corona tests work?
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The standard: RT-PCR
The best validated and most accurate tests against the virus are the RT-PCR tests, which are currently used to test for Covid-19. These tests, developed on the basis of the Sars-CoV-2 gene sequences, including that of a team led by Christian Drosten at the Berlin Charité, show the genetic makeup of the virus. The abbreviation RT-PCR describes the process of this procedure.
In the first step, reverse transcription (RT), the virus RNA is translated into DNA. This is necessary because the second step, the polymerase chain reaction (PCR), only works with DNA. Short strands of DNA, called probes, which bind precisely to individual areas of the virus' genetic material, work together with a protein called polymerase to ensure that only the pathogen's genetic material is exponentially multiplied. When that happens, another component releases a flare.
Which regions of the virus genome the DNA probes recognize varies from test to test; that of the Charité recognizes regions of the E gene, which is typical for all coronaviruses, as well as RdRp, the code for an enzyme that replicates the virus genome. It is important that the selected areas are so specific for Sars-CoV-2 that the test responds to the virus being searched for, but not to related viruses such as Sars or the human coronaviruses.
RT-PCR is the most sensitive of the coronavirus tests. Thanks to the exponential multiplication, the test responds to even very small amounts of virus. This method only requires about five to ten copies of the virus RNA for a positive detection. The method is based on a well-known and widely used technique that delivers the result within a few hours. If the RNA of the virus is found in the throat of a patient with a cough and fever, one can assume that it is Covid-19.
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The disadvantages of RT-PCR
However, there are some pitfalls - the smear must be taken correctly, which is not necessarily the case with a self-test at home. In addition, the amount of virus in the throat can fluctuate greatly during infection - especially later, when the virus is mainly in the lungs, the cotton swab may no longer detect viruses at all. Conversely, the evidence after the disease has ended can still be positive and pretend that the patient can still infect others. But the PCR test says nothing about how contagious someone is.
It is also not possible to determine in this way whether the genetic material is undamaged and whether the sample contains active viruses. This is also a problem for how long the virus survives on surfaces. The report that Sars-CoV-2 was still detected on the Diamond Princess after 17 days was based on the PCR process. It is therefore unclear what the finding actually means.
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