PCR tests were used already at the beginning of the covid-19 pandemic. SARS-CoV-2 is an RNA virus. However, PCR can only detect DNA. Therefore, RNA is first transcribed into DNA. Next the DNA is specifically amplified. A high viral concentration generates a strong signal. This allows to use a PCR test to detect or exclude an infection by SARS-CoV-2. The analytical sensitivity of PCR tests can vary...
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