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Ok, listing out my issues with this article for non-scientists here:
1. Virus load in a nasal swab is very variable. Flu studies have even found differences in virus loads depending on whether the sample was taken from R or L nostril, the collection volume of the swab etc. https://twitter.com/apoorva_nyc/status/1299705092178956288">https://twitter.com/apoorva_n...
1. Virus load in a nasal swab is very variable. Flu studies have even found differences in virus loads depending on whether the sample was taken from R or L nostril, the collection volume of the swab etc. https://twitter.com/apoorva_nyc/status/1299705092178956288">https://twitter.com/apoorva_n...
2. Given this variability, it is obviously safer to use a reasonably low bar for positivity (i.e Ct <40) because the virus load in the body is > than the load in the swab which is > than the load in the collection tube which can be > than the load actually tested.
3. Ct values aren& #39;t a really measure of virus load in the patient in a test like this where there& #39;s no comparison with a host gene possible. (RNaseP levels are very variable)
4. Plus the load changes as infection progresses so you really can& #39;t be too stringent with thresholds.
4. Plus the load changes as infection progresses so you really can& #39;t be too stringent with thresholds.
4. This is why the tests for H1N1 also use a high Ct (37-38) for positivity. Something the journalist could& #39;ve easily looked up.
5. My point: scientists who come up with these tests aren& #39;t stupid. They just have to deal with different challenges from academic scientists.
5. My point: scientists who come up with these tests aren& #39;t stupid. They just have to deal with different challenges from academic scientists.
6. Yes, in an academic setting you& #39;d probably ignore/re-test a Ct of 40. But the stakes are different.
7. Caveat: I& #39;m not an immunologist or diagnostician (I have done virology research in
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🌱" title="Setzling" aria-label="Emoji: Setzling"> and 1000s of RT PCRs)
7. Caveat: I& #39;m not an immunologist or diagnostician (I have done virology research in
8. It took me no time to think of these questions, and it& #39;s worrying that neither the journalist or the scientists interviewed brought up these issues.
In any case to go from this article and conclude that "90% (!!!) of positives are not contagious" seems laughable.
In any case to go from this article and conclude that "90% (!!!) of positives are not contagious" seems laughable.
To the extent that the article suggests we need to more periodic testing with less sensitive rapid test kits, sure, let& #39;s talk about that once we have capacity to swab everyone at least just once!
Also, I& #39;ll happily delete any of these if someone shows me my take is wrong as this is just a bit far from my expertise.
