Covid-19, duration of viral shedding, and infectiousness: meta-analysis

Re:Covid-19, duration of viral shedding, and infectiousness:... by gregwebs on Monday November 23, 2020 @09:25AM (#25187010)

The issue is that a PCR test does not actually tell us if a virus particle is live or inactive. A shed virus particle can still have intact RNA for the region tested by PCR.

There are published case reports where someone has tested PCR positive during an infection, then PCR negative, and then PCR positive again later and the explanation given has been that they did not get re-infected and their infection did not flare back up but just that virus had been continually shed and the later test was able to capture that.

edit: s/DNA/RNA. The PCR process actually operates on DNA so the virus RNA is converted to DNA as the first step of RT-PCR.

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Re:Covid-19, duration of viral shedding, and infectiousness:... by SomeoneFromCA on Monday November 23, 2020 @09:26AM (#25187027)

Covid is not a DNA virus.

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Re:Covid-19, duration of viral shedding, and infectiousness:... by westwing on Monday November 23, 2020 @11:13AM (#25188273)

The PCR thresholds are chosen to minimize false negatives, not false positives. A sample that required 30+ replication cycles is unlikely to come from a person that is infected/infectious, yet it would be counted as "positive". The thresholds are derived from experiments under lab conditions, providing a safe lower bound.

That does put into question the validity of counting PCR test positives as a benchmark of viral load among the population, but as a safety measure for potentially infected individuals, the trade-off is worthwhile.

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