Twice in as many days, again a 🧵 examining a specific document. This time, I am not very impressed with the document. The document being -
"Should all healthcare workers caring for patients with COVID-19 wear FFP3?"
ips.uk.net/post/news/shou…
1/n
"Should all healthcare workers caring for patients with COVID-19 wear FFP3?"
ips.uk.net/post/news/shou…
1/n
2) Conflicts/Bias - I do not know the author of the document, and I am seriously biased against messy reviews of selective evidence.
3) The title is as a question. My observation - If you are asking this question, you already have an answer in your head "NO" and your entire effort is going to be to justify that answer.
HCWs deserve the best protection available, period.
HCWs deserve the best protection available, period.
4) I am jumping a little ahead towards the end of the document, but this relates to the first point. All these and more points discussed in the concluding pages of the document are logistics issues. They should not help decide on evidence if a certain protection is needed 
5) This is like my pothole theory of driving: get the city to repair potholes. Do not stop driving or decide to generate energy from the vibrations of your car going into potholes.
Again, if you are arguing logistics, you already have an answer you want to defend.
Again, if you are arguing logistics, you already have an answer you want to defend.
6) The aerosols generated do contain a significant amount of virus. The author is playing to an old bias here that virus content is proportional to the size of the droplet. There is no evidence of this.
7) thelancet.com/journals/lanre…
Really nice work, compiling evidence on content of pathogens in different sized droplets.
Really nice work, compiling evidence on content of pathogens in different sized droplets.
8) A table and an image form above work. The evidence being that actually smaller droplets are more likely to have a higher viral load and typical breathing/coughing produces mostly small droplets (aerosols)
9) Here, apart from repeating the baseless idea that larger droplets should have more virus load, author reference to Zhang and Duchane
10) Actually, the main take home message from Zhang & Duchane seems to be that we should also give importance to short range, aerosol particles.
11) Zhang and Duchane do discuss the virus content, but they are referring to someone else's model - Stadnytskyi et al.
12) Stadnytskyi et al. have a very different take home message than the author of the document we are discussing wants so they were not directly referred to. pnas.org/content/117/22…
13) More of their findings:
And they do actually say that talking for 1 min... bit. But they also assumed viral load is proportional to size, leading to their iffy conclusion.
And they do actually say that talking for 1 min... bit. But they also assumed viral load is proportional to size, leading to their iffy conclusion.
14) Two at once - coughing does not necessarily generate more of larger than 5 micron particles than smaller than it. And two, larger particle does not always have more virus.
15) Now, back to R0 denialism. By the way, the publication is not that recent
17) And just in case you want to see how infectious #COVID19 can be, here is a long list
https://twitter.com/Orla_Hegarty/status/1352913377094475776
18) This is a pet peeve of @DRTomlinsonEP
Unless the virus loaded particles have developed sentience, why would anyone think that different laws of physics guide their behaviour in a lab, as opposed to every other place?
Unless the virus loaded particles have developed sentience, why would anyone think that different laws of physics guide their behaviour in a lab, as opposed to every other place?
19) Perhaps, a step change (not an incremental change) in the rigour of application would be use of better masks? But what do I know, English is not my first language.
20) Why this question? If there is some evidence to this, why are you asking this question and willing to take chances?
21) So, did everyone just find RNA, no culturable virus?
22) Zhou et al. sound concerned that they found so much RNA everywhere. Now, virus sampling and getting viable virus is tricky. So, while maybe Zhou et al. did not, what about others?
23) sciencedirect.com/science/articl… these guys are really good at this sampling stuff. They developed a sampler to make sure they can catch the virus, intact, in the act.
24) More intact virions and more evidence of more virions in smaller particles medrxiv.org/content/10.110…
25) More evidence on your breath being loaded with this virus stuff - more so than surfaces 🤔
27) Just before I forget -
pubmed.ncbi.nlm.nih.gov/21300628/
Concentrations and size distributions of airborne influenza A viruses measured indoors at a health centre, a day-care centre and on aeroplanes
More evidence on smaller particles have more...
pubmed.ncbi.nlm.nih.gov/21300628/
Concentrations and size distributions of airborne influenza A viruses measured indoors at a health centre, a day-care centre and on aeroplanes
More evidence on smaller particles have more...
28) Also, this one
jamanetwork.com/journals/jaman…
"A total of 81 viral cultures were performed across 5 studies, and 7 (8.6%) from 2 studies were positive, all from close patient environments."
More viable virus in air
jamanetwork.com/journals/jaman…
"A total of 81 viral cultures were performed across 5 studies, and 7 (8.6%) from 2 studies were positive, all from close patient environments."
More viable virus in air
29) If you started assuming there is no viable virus to be got from air and then there are a bunch of studies showing otherwise, what should you do? Stick to your guts or change your views?
30) Again, an unreasonable question because they set out with an answer.
31) Let us give some evidence nevertheless
Australian data on infections among HCWs
Australian data on infections among HCWs
https://twitter.com/NjbBari3/status/1366899359208513538
32) academic.oup.com/ofid/advance-a…
SARS-CoV-2 infection among healthcare workers despite the use of surgical masks and physical distancing - the role of airborne transmission
SARS-CoV-2 infection among healthcare workers despite the use of surgical masks and physical distancing - the role of airborne transmission
33) medrxiv.org/content/10.110…
Healthcare workers’ high COVID-19 infection rate: the source of infections and potential for respirators and surgical masks to reduce occupational infections
Healthcare workers’ high COVID-19 infection rate: the source of infections and potential for respirators and surgical masks to reduce occupational infections
34) and then, somehow, the author wants to reference this document which very clearly talks about close range and longer range aerosols 🤔
I am confused, this seems to be a nice collection of evidence contradicting the stand of the document?
I am confused, this seems to be a nice collection of evidence contradicting the stand of the document?
35) Also there is a bunch of stuff about aerosols generating procedures so just go nuts with these studies which say AGPs are not all they are made out to be
…-publications.onlinelibrary.wiley.com/doi/10.1111/an…
A quantitative evaluation of aerosol generation during tracheal intubation and extubation
…-publications.onlinelibrary.wiley.com/doi/10.1111/an…
A quantitative evaluation of aerosol generation during tracheal intubation and extubation
36) medrxiv.org/content/10.110…
The effect of respiratory activity, ventilatory therapy and facemasks on total aerosol emissions
The effect of respiratory activity, ventilatory therapy and facemasks on total aerosol emissions
37) Finally, no one said anything about putting all your eggs in one basket. Get them better masks and ensure all other IPC measures are also being followed. But do not do this half-hearted thing of lecturing HCWs
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