Bao et al’s claim to meet Koch’s Postulates is no more than modern day Alchemy undertaken with very sophisticated instrumentation, untested assumptions and poor research design. Implicating in the laboratory is not the same as fulfilling. And that’s what is happening throughout these epidemiologically-based/intoned papers purportedly ‘showing’ ‘SARS-CoV-2 causes ‘Covid-19 disease’ based on putative isolation, no viral purification as well as biased and untested assumptions. ‘Imputed suspicion’ then starts to crumble [as below] when one looks closer at the research designs and the huge claims made – it’s a ‘Covid-Dazzler’. Huge claims are then found to be at worst false or at best spurious; these are “facts” that disappear as one looks closer. It reminds me of Agatha Christie’s comment: 

“The truth, however ugly in itself, is always curious and beautiful to seekers after it.” —The Murder of Roger Ackroyd. 

This claim that Bao et al fulfils Koch’s Postulates is questionable because of the following research design and interpretation flaws:

1. Random allocation was not undertaken; the control group was a ‘mock treated’ group. As there was no randomization this can only be a quasi-, not a true, experiment. This means the mock+quasi-experimental group may not have been equivalent from the start, further implying that any causal connection inferred from the study analysis is confounded by this problem of internal validity. 
2. Bao et al say X [SARS-CoV-2] ‘highly homologous’ with Y [severe acute respiratory syndrome coronavirus SARS-CoV human angiotensin-converrting enzyme 2 (hACE2) the entry entry receptor of SARS-CoV] by molecular analysis, so used Y [transgenic/wild type mice] to study X  [lines 50 -54] based on this assumption that hACE2 is the entry receptor; the latter assumption was never tested in the research design; the reader is expected to accept that this underlying assumption is true, that is, believe that it is correct, a priori.
3. How did Bao et al know their starting sample were ‘pathogen free’ [line 56]? Again no evidence no test given just an untested assumption that we must believe
4. [now I’m thinking reading this paper - like Mulder in the X-Files - ‘I Want To Believe’ - but I’d like the evidence first?]
5. No virus 'isolated' [or 'purified' see White and Fenner (1986) p655] from the supposedly inoculated experimental and control group mice [WT-HB01  + ACE2’Mock mice line 79], a finding which they suggested meant one thing [hACE2 was essential] but it could have other interpretations, which are never explored.
6. Only one interpretation of the reported data was given [line 79] and again the reader has to believe this is the correct interpretation, and other interpretations not reported, and are left hanging in the reader’s mind. Failure of peer review.
7. line 70 - 'detected' viral loads in the controls but not the experimental group - data not shown, why? [is that because it conflicts with the underlying belief of the authors? It could have been included in a ‘limitations section’ but I couldn’t see one or any reference to ‘limits of our study’ so it is implied Bao et al’s study has no limitations, again another failure of peer review.]
8. [line 214] RT- PCR sequences not presented but 'available on request' [okay not enough room [ok, so I’ll have to request them if I eventually want to check? N.B.– requested but not received]
9. [line 225] the ELISA OD the cut-off is not reported, so how a 'positive' is determined is not evident.
10. Vero E6 cell culture [line 276] is not “isolation” or 'purification' (White and Fenner 1986 p655).
11. Unclear what Bao et al mean by viral ‘isolation’ – looks like ‘passage through cultures’ - that is not the same as viral experts define 'purification' (White and Fenner (1986) p655) - as seems to be defining isolation [line 342] using Vero E6 cells.
12. [line 333] Image of virus seems to be measure <200nm as claimed for ‘SARS-CoV-2’ but only one 'viral particle' shown; no field(s) of purified particles.
13. The biological role or even existence of amplified sequences or inferred microorganisms remains unclear. And in the absence of a purified intact microorganism this prevents experimental reproduction of the disease [see Fredericks, D. N. and D. A. Relman (1996). "Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates." Clinical Microbiology Reviews 9(1): 18-33.] So one must go with the original Koch’s Postulates [if one claims "That's old hat, we've updated Koch’s Postulates for modern times’ then we need to read Fredericks and Relman (above)].
14. [line 166] In Bao et al "The SARS-CoV-2 (strain HB-01) was "kindly provided" by Professor Wenjie Tan [1] from the China Centers for Disease Control and Prevention (China CDC)" [my empasis]. Reference 1 is Zhu et al.  Zhu et al, did not publish evidence for the purification of the COVID-19 virus. So Bao et al, could not have fulfilled Koch Postulates because what he got from Professor Tan did not fulfil the second postulate: "The organism must be isolated from a host containing the disease and grown in pure culture."  In fact, Zhu et al said: "Although our study does not fulfill Koch’s postulates, our analyses provide evidence implicating 2019-nCoV in the Wuhan outbreak". [Why did Zhu say “implicated”?  Because most likely he knew the research hadn't fulfilled Koch’s Postulates.  Zhu could not have fulfilled the Koch’s Postulates because he did not fulfil the second Koch Postulate. 'Implicated' seems a useful umbrella concept for critiquing.]

References

White DO, Fenner FJ. (1986) Medical Virology. San Diego, Academic Press.

Dr Kevin P Corbett, London, England.

First written 27 April 2020

Revised 19 June 2020