I'm by no means an expert but the pcr testing is inadequate because it simply captures genetic material,what are they comparing that to,since there's never been a a gold standard to compare it with initially? Dr. Andrew Kaufman gives his insight here.
Regarding Koch's postulate, whether it's the 1937 Rivers-modified or the original from 1890, the postulate is borderline useless today. These days we have high-throughput DNA and RNA sequencing, PCR, ELISA, protein sequencing, electron microscopies and other more highly precise tools. There has been an ever increasing list of organisms or viruses that have become the exception to Koch's postulate when determining disease causality.
When the Nature article was published in 2003 regarding SARS-CoV-1 (SARS) meeting the Rivers-modified criteria, sure, it was great that it met those criteria and it was possibly helpful in determining the virus' etiology. But at that time, high-throughput DNA/RNA sequencing had not taken off commercially until the mid to late 2000's. Now determining whether it meets Koch's postulate or it doesn't, it adds little value in determining casuality today. Despite Kaufman's focus on psychiatry for at least the last decade and half and not on molecular biology or microbiology, I'd expect more from him. Either he's just ignorant or he's willfully ignorant.
Kaufman also brings up the possibility of exosomes being the causal agent in the slides. Admittedly, I had to look whether exosomes can confer an immune response even though it's endogenously made, and yes, it's possible. However, what was found in the isolated particle is a surface S (spike) protein very structurally similar to those found on the surface of those viruses found belonging to the coronavirus family. One can suggest that's a coincidence, but I am sure has conclusively determine that's an S protein from a coronavirus through mass spectrometry and proteomic sequencing. So there are now two possibilities, either a) it's a coronavirus, or b) a coronavirus infected that cell, incorporated it's genetic payload to that cell's genome, synthesized the S protein, and part of that cell was shed off as vesicle that forms an exosome that has the S protein on it. Both would confer an immune response and eventual antibody production by the B cell. But it's unlikely the latter is the causal agent because the latter will not cause the pathogenic cellular destruction like we've seen on chest X-rays and renal glomerular biopsies. In either scenarios, that person is infected with coronavirus and either is affected or is an asymptomatic carrier.
Now regarding having the original viral samples from the Hubei province, I agree it'd be advantageous to have that rather than just the genetic sequence. Geopolitical and finger-pointing aside, this would be helpful in understanding the origin of the virus by tracing how a zoonotic virus jumped from animal to human. I've not been following that front as much, but last I heard it was either a bat, civet, or pangolin. Have there been any additional culprit or conclusion? Last I heard, the virus found in pangolins had about 99% commonality to the virus in Western U.S. Frankly, while I don't think it's been "bioengineered," with some additional reporting in the last 2 months, I can no longer rule out whether the virus "escaped" from the lab in Wuhan. That is very much a possibility, IMO. Either way, a wholesome, unbiased investigation ought to have taken place, but I doubt the CCP would allow that even before international relations turned to their current icy state.
TL;DR:
1) Koch postulate is not the gold standard method in determining disease causality today because of more precise tools in helping confirm or strongly determine causality. Frankly, someone that should know better who thinks that being a major factor has me questioning whether they are truly being inquisitive in good faith or have some sort of agenda to push.
2) The exosome theory doesn't sound solid to me. Exosomes would not lead to the pathogenecity that has been documented.
3) And it'd be nice to have the original sequence from the first 25-50 patients in the Hubei province, or better yet, from patient zero. We don't because either it was incidentally or willfully, depending on one's level of skepticism, destroyed, so we work with what we have, and what we have are isolated viral genomes from patients that have 99% genetic biosimilarity to coronaviruses found in pangolins.
