1/ A big COVID outbreak takes 2 ingredients:

- someone highly infective (most infected people don't seem to be infective or little; the highly infective are so during a short period)

- The right indoor conditions for accumulating and breathing in the virus.
2/ In this paper we showed that the outbreaks that have complete data for analysis are explained by airborne transmission in shared indoor air

[Detailed explanation on that thread]

3/ The level of virus in the air is analogous to the level of water in a sink, depends on:

- faucet: emission rate of virus

- size of sink: volume of room

- size of drains: ventilation, filtration etc.

[Analogy not perfect but good for illustration]

4/ The emission rate of the virus depends on:

- Viral load / aerosol emission rate of the infected person(s). Very highly variable in time and between people.

- How much time they spend in space

- Vocalization: far more emission if talking, even more if yelling singing
5/ Virus emission also:

- seems to increase with heavy breathing, e.g. exercise in gyms.

- And decreases with masking (some with cloth, more with surgical, a lot more with well-fit N95)
6/ Then how much virus is breathed in by the susceptible people (SP) present depends on:

- The level of virus in room (sink analogy in prev. tweet)

- How much time SP spend in the space

- Breathing rate of SP (e.g. low if sedentary, high if dancing, gym...)

- masking of SP
7/ You can combine all those effects rigorously (*) into single number: Relative Infection Risk Parameter (Hr)

*: within approximation that the air mixes faster than people enter and leave the space, as e.g. with someone lighting a cigarette in a room

8/ The attack rate on the outbreaks from the scientific literature (famous restaurant, choirs, buses, call center, meat packing, schools...) falls in line with Hr.
9/ So not a mystery where the outbreaks happen, we know the conditions that favor them (same as 3 Cs of Japan or many other studies: nature.com/articles/s4158…).

But very random whether an outbreak will happen, depending on infrequent highly infective individuals being present
10/ Definitely not surprising that cars and buses can have a lot of outbreaks, since they are small "rooms" with significant time spent there, and many of them are poorly ventilated

11/ This is explained in our recent @ConversationUK article (led by @trishgreenhalgh) where we provide this chart:

[You can see numbers and modify chart at tinyurl.com/COVID-Tables]

theconversation.com/heres-where-an…
12/ We have a short paper under review where we propose that Hr should be calculated for all indoor public spaces and posted (for typical use without mitigations, with various mitigations). And then use that to guide mitigations, occupancy etc.
13/ Now, given how slow Public Health has been to accept airborne transmission during the pandemic, I won't hold my breath till this approach or something like it is put in place widely.

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More from @jljcolorado

Jan 24
1/ @Nature: "COVID-19: endemic doesn’t mean harmless"

"The word ‘endemic’ has become one of the most misused of the pandemic. And many of the errant assumptions made encourage a misplaced complacency."

By @ArisKatzourakis

nature.com/articles/d4158…
2/ "A disease can be endemic and both widespread & deadly. Malaria killed more than 600,000 ppl in 2020. 10M fell ill with tuberculosis that same year & 1.5M died. Endemic certainly does not mean that evolution has somehow tamed a pathogen so that life simply returns to ‘normal’"
3/ "There is a widespread, rosy misconception that viruses evolve to become more benign. This is not the case: there is no predestined evolutionary outcome for virus to become more benign, especially ones, such as SARS-CoV-2, in which most transmission happens bf severe disease"
Read 6 tweets
Jan 23
Of course it is neurotropic, see e.g.: pubmed.ncbi.nlm.nih.gov/34189535/

70 years ago this fellow would have told us that polio was not neurotropic, because only 1% of the cases have serious complications of that type...
Read 5 tweets
Jan 23
Of course children need masks. COVID is not a cold. It is a neurotropic virus, can go into the brain and lots of other organs. 1000 children dead in US, millions of kids w/ #LongCovidKids, millions have lost parents.

Wearing mask is not hard for kids, they forget about it.
And this person is a doctor? And @BBCNews gives a platform to an someone with this level of ignorance?
Read 20 tweets
Jan 21
1/ Sobre la transmisión de virus a muy gran distancia, como decía este señor que podía explicar que hubiera e.g. más casos en Cataluña vs. otras comunidades.

He dicho que es una tontería, y lo mantengo. Explico algunos detalles aquí:
2/ Esta es una pandemia DE INTERIORES. El virus se transmite por el aire, pero sobre todo hablando cerca o al compartir una habitación (como todos los casos de superpropagación), como en la imagen.

Muchos más detalles aquí:
3/ Hay bastantes casos documentados de transmisión por el aire a más distancia en interiores (sin estar en la misma habitación al mismo tiempo), por ejemplo en hoteles de cuarentena en Nueva Zelanda, Hong Kong etc. Como este caso por flujos bajo puertas:

Read 13 tweets
Jan 20
1/ THE PENDULUM OF HISTORY OF AIRBORNE TRANSMISSION

As we revise our paper on this (papers.ssrn.com/sol3/papers.cf…), we've added draft diagram to summarize the history visually:

It'll be a few more days till we submit, so please reply with comments, clarifications, suggestions etc.
2/ If you haven't seen this, the short version:

- From Hippocrates and during most of human history, diseases were thought to transmit through the air (via a miasma)

3/ Miasma theory dominates till mid to late 1800s:

Cholera, Puerperal Fever, and Malaria (literally "Bad Air" in medieval Italian) were thought to transmit through the air. But demonstrated to transmit via water, hands, and mosquitos, respectively.

Read 19 tweets
Jan 19
@CIBSE_NatVent I have run the case on our estimator at docs.google.com/spreadsheets/d…

- Note ventilation rate is relatively high, most schools don't meet it

- Leads to CO2 = 1720 ppm, while some of your colleagues in the UK say it is fine if it is < 5000 ppm

Vent rate for 5000 ppm is 1 l/s/p, NOT 5
@CIBSE_NatVent With 5 l/s/p, adding the RELATIVELY SMALL cleaner with CADR = 100 l/s (ACH = 2.4 on cell B31) the risk goes down 30%

With an EXPONENTIALLY growing disease, that's a lot, because it is 30% off EACH GENERATION. I.e. compound interest
@CIBSE_NatVent With the "barely acceptable according to some UK experts" case with 4999 ppm CO2 (~1 l/s/p), then adding that smaller air cleaner reduces the risk 45%.

I would definitely prefer to have my son in a class with the cleaner than without the cleaner
Read 5 tweets

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