The code number for how contagious a person infected with SARS-CoV-2 is the Ct-value (“cycle threshold”), which is determined in a PCR test. It is calculated from the number of times a sample (nasal/throat swab) must be repeated in the laboratory to detect the virus. The more often the procedure is used to find pathogens, the fewer of them are present – i.e. less of them are passed on. If there is a high viral load, a positive result is seen earlier, and the person affected is considered to be (highly) infectious. Only from a Ct-value of 30 one currently gets the information: “not infectious”. According to the Robert Koch Institute (D), this explains the confusing situation that people with a positive corona PCR test can be sent home without consequences.
Experts from MedUni Innsbruck also emphasise that the Ct value is high at the beginning of an infection, but as the disease progresses, there is a risk of infection for others after just a few days. By then the patient has already been lost sight of. A second test is recommended as a precautionary measure, or a 10-day quarantine is recommended even if the Ct value is inconspicuous.
- hp, with reports from krone.at. picture: pixabay.com
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