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Message: <blockquote data-quote="imhotep" data-source="post: 26747367" data-attributes="member: 562115">This is an extract from a post I made in 14 November 2020 - on the interpretation of the Ct values... This figure clearly shows how the Ct values can reflect on infectivity.<snip>On a previous post on a Covid Megathread, I have explained in detail how a RT-PCR is done. The Ct value does play a part. The Ct is what's known as the Cycle Threshold - is the number of Cycles needed for the fluorescent signal to cross the threshold above the background. A PCR is done usually to a max of 40 cycles...Cts < 29 are strong positive reactions indicative of abundant target nucleic acidCts of 30-37 are positive reactions indicative of moderate amounts of target nucleic acidCts of 38-40 are weak reactions indicative of minimal amounts of target nucleic acid which could represent an infection state or environmental contamination.So a high CT value is dubious.  You cannot rely on Ct after 37 at all. In which case you do another PCR test a few days later. These can be false positives.A team of scientists recently did a study more than 3000 cases the graph below shows the results. Ct against infectvity. They did a PCR test and also they did a viral culture using the same swab to independently grow the virus to confirm. The number of Samples N is the PCR test, The number of Samples n is the Virus detected in the culture.One can easily see at high Ct values the results are inaccurate. The Global percentage value graph is 100% at low Ct values and then keeps on falling down to zero at Ct around 36. This is well known but only probably not known by an average person.Also studies done in several countries (most recently in Brazil) has shown that nearly 35% of patients Ct value of 25 or below were more likely to have severe disease or die. <snip>[ATTACH=full]138922[/ATTACH]</blockquote>

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