RE: Covid tests too sensitive?31 Aug 2020 12:56
Excerpt from the article.
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Experts say a reasonable cutoff for the virus would be 30 or 35 cycles, according to Juliet Morrison, a virologist at the University of California, Riverside.
Mina said he would set the cutoff at 30.
New York's state lab Wadsworth analyzed cycle thresholds values in already processed COVID-19 PCR tests and found in July that 794 positive tests were based on a threshold of 40 cycles.
With a cutoff of 35, about half of those tests would no longer qualify as positive. About 70 percent would no longer be judged positive if the cycles were limited to 30.
In Massachusetts, from 85 to 90 percent of people who tested positive in July with a cycle threshold of 40 would have been considered negative if the threshold were 30 cycles, Mina said.
'I would say that none of those people should be contact-traced, not one,' he said.
The Food and Drug Administration said that it does not specify the cycle threshold ranges used to determine who is positive and 'commercial manufacturers and laboratories set their own.'
The Centers for Disease Control and Prevention said it is examining the use of cycle threshold measures for 'policy decision'.
The CDC said its own calculations suggest its extremely hard to detect a live virus in a sample above a threshold of 33 cycles.
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MS