Quote:
Originally Posted by Sephiroth
@jonbxx
Jon - you might know the answer.
Let's say that a CV sufferer of a couple of months tests positive at that point. That sufferer appears to be recovering.
Some people are saying that although testing positive, the sufferer is no longer contagious. Is that right? Can the swab test differentiate between active and inactive virus cells? Logic tells me that whatever the sufferer is spewing out at that point would be contagion unless virus cells detected were inactive.
Cheers.
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I can answer that, no problems. The current COVID RT-PCR test looks for SARS-Cov2 RNA only. When you have a swab taken, the swab is put in to a solution full of nice ingredients which break down the virus including the proteins around it. This opens things up for testing and stabilises the RNA.
We are full of enzymes which happily break down RNA and this is a good thing. RNA is how we make proteins so you make RNA to make proteins and the enzymes which break down RNA are an 'off switch', stopping the protein manufacture. RNA in cells doesn't hand around long with a half life usually of minutes to hours. Again, this is a good thing. The mRNA vaccines have had their mRNA modified to slow down the rate they are broken down in the cell
Now, the virus could be inactive in that it can't get into cells but still be picked up by the COVID test. The big question is how long would virus hang around in the usual places for a test swab. The inside of the nose and back of throat are designed to trap and kill nasties so the environment is pretty harsh but it's certainly not impossible for some virus to hang around.
A big deal is made of the 'number of cycles' for a COVID test. The test makes copies of DNA from the SARS-Cov2 RNA, DNA being easier to handle. It's the DNA we are measuring during a test. Each cycle of making more DNA amplifies the amount present until you can measure it. However, the more cycles you have, the more chance of picking something up that isn't really there by mistake which could give you a higher false positive rate.
So yes, the current COVID test could pick up false signals from RNA from dead virus and if you push things too hard, you can get false positives from nothing. The unknown thing here is how long SARS-COV2 RNA will hang about in a throat or nose. the general feeling is not long.
You could try and culture virus from suspected COVID patients but this is hard and time consuming. It could a couple of weeks to get a result so at present, the RT-PCR test is the best we have