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Prof. Jose-Luis Jimenez Profile picture
@jljcolorado
Aug 23, 2022 • 143 tweets • 76 min read • Read on X
1/ What were the historical reasons for the resistance to recognizing airborne transmission during the COVID-19 pandemic?

Our peer-reviewed open-access paper is now published:

onlinelibrary.wiley.com/doi/10.1111/in… Image
2/ Soon after COVID-19 pandemic started, it was clear to many scientists (inc. those who understand aerosols) that AIRBORNE trans. was an important contributor

E.g. as soon as we talked to the Skagit choir, it was obvious that was airborne-dominated:

doi.org/10.1111/ina.12…
3/ However, major public health organizations such as @WHO and @CDCgov were in complete denial, saying that airborne transmission was MISINFORMATION!

(Disgracefully, @WHO has not deleted this tweet or clearly stated that it was an ENORMOUS error)

Image
4/ How was that possible?

- Many scientists are concluding that airborne transmission is important
- Major public health organizations such as @WHO say that it is misinformation!

Historical trends and errors (this thread) are important to explain this, but NOT the only reason
5/ This major error (IMHO one of most important errors in the entire history of Public Health) has had major consequences:

- In early pandemic we focused on surfaces, which are minor or negligible
- we ignored air, which was the dominant mode

=> lack of controlling transmission
6/ Since then, research has clearly shown that airborne transmission is the DOMINANT mode of transmission of COVID-19:

thelancet.com/article/S0140-…
7/ To this day, 0 proven cases of surface transmission

And droplet transmission has NEVER been demonstrated, not just for COVID-19... but for ANY disease in the history of medicine!

[Paper from Prof. Yuguo Li, member of @WHO IPC Committee]

sciencedirect.com/science/articl… Image
8/ So how did we get into this mess?

PH organizations tell us that unproven transmission mechanisms are dominant, and that the dominant trans. mechanism is misinformation

We'll soon delve into the history in our paper.

onlinelibrary.wiley.com/doi/10.1111/in…
9/ But before we go into the history, there are other reasons to review.

Most importantly, surface-droplet transmission is very CONVENIENT to those in power. And AIRBORNE trans. is an inconvenient truth (just like climate change, dealt with similarly)

telegraph.co.uk/global-health/… Image
10/ There is at least one more reason for the resistance:

those who made this enormous error at @WHO, its IPC committee, @CDCgov, & health ministries around the world DO NOT WANT to admit their error

Govt advisor privately: "we need to find a way to allow us to save face"
11/ And those Public Health officials that continue to resist and obfuscate about airborne transmission are in control of the PH institutions.

Aerosol scientists are almost complete outsiders, and have been almost systematically excluded to this day.

wellcomeopenresearch.org/articles/6-126 Image
12/ So what about the contribution of history to the denial of and resistance to airborne transmission by Public Health authorities worldwide?

It is summarized in this diagram, which I'll explain in this thread:

onlinelibrary.wiley.com/doi/10.1111/in… Image
13/ Sorry, I need to take a break for some meetings (we are starting classes this week at @CUBoulder). I'll continue with the thread in 1 hr.

If you can't wait to read it, it is all in the paper:

onlinelibrary.wiley.com/doi/10.1111/in…
14/ So to understand the errors that led to the denial and resistance of #COVIDisAirborne, we need to go back to Hippocrates! (~400 BCE)

en.wikipedia.org/wiki/Hippocrat… Image
15/ Hippocratic writings in ancient Greece first proposed that diseases were caused by imbalance of humors in the body, which could be triggered by a “miasma” transmitted through the air

loebclassics.com/view/hippocrat… Image
16/ Throughout much of subsequent human history, the belief persisted that diseases were transmitted through air

Because the actual agents remained a mystery for centuries, explanations were given in general terms such as “miasmas,” or “bad air”

en.wikipedia.org/wiki/Miasma_th… Image
17/ For example, the etymological root of the term "malaria" (a disease that we now know is transmitted by mosquitos) is “mala aria,” medieval Italian for “bad air”

doi.org/10.1186/1475-2…
17/ Some origin theories were more specific. E.g. Roman scholar Varro (116–27 BCE) wrote that swamps were a particular breeding ground for minute creatures that “float in the air and enter the body through mouth & nose and there cause serious diseases.”

doi.org/10.1186/1475-2…
18/ Thus it became a policy of the Roman Empire to drain swamps, removing breeding grounds for mosquitos, reducing malaria, an example of a mistaken theory giving good results

and increasing faith on the theory

We see this many times through history

doi.org/10.1186/1475-2…
19/ The concept of person-to-person contagion came much later, most clearly in work of Italian physician Girolamo Fracastoro in 1546

[This is actually a subject of current debate, with some scholars thinking that the role of F may have been overstated]

en.wikipedia.org/wiki/Girolamo_… Image
20/ What ensued after Fracastoro, however, was a centuries-long debate between “miasmatists,” who held fast to the idea that diseases floated through the air over distances, and “contagionists,” who accepted person-to-person spread of disease

sciencedirect.com/science/articl…
21/ Because it was (and it still IS) very difficult to determine how, why, and from where someone became infected, the miasmas vs. contagion debate failed to reach a resolution and persisted for centuries.
22/ A middle ground was proposed, “contingent contagionism”: malaria, or cholera might be contagious in an impure atmosphere, but not in a healthy atmosphere

This idea therefore captured some grains of truth (eg. now we know ventilation reduces airborne)

archive.org/details/390020…
23/ Miasma theory was dominant till the mid/late 19thy Century. Florence Nightingale (1820–1910) like most Victorians was raised to believe that diseases were caused by ‘miasma’ or foul air.

en.wikipedia.org/wiki/Florence_… Image
24/ In her Notes on Hospitals, Nightingale referred to the idea of contagion as absurd:

[She was nevertheless very practical and effective in reducing disease, e.g. with ventilation and phys. distance, and later accepted germ theory, as we'll see later]

play.google.com/store/books/de… Image
25/ We enter a critical period around 1850. Miasma theory is still dominant, although contagion (mostly through the air) also has proponents.

Microorganisms have been observed for 2 centuries since the invention of the microscope, but haven't clearly been connected to disease
26/ Cholera strikes London in 1854.

The public health establishment believed it to be caused by a miasma. English sanitary reformers (e.g. Chadwick), who initiated many modern public health practices, found miasma appealing, as it appeared to explain...

en.wikipedia.org/wiki/Edwin_Cha… Image
27/ ...the prevalence of diseases in the undrained, filthy, and foul-smelling areas where the poor lived, and helped justify their efforts to address those conditions.

[They had made a huge error, and they resisted accepting it, just as @WHO today]

doi.org/10.1136/bmj.32…
28/ John Snow was a wealthy doctor but outsider to public health.

His work in anesthesia made him familiar with the behavior of gasses. He realized that the spread of chlore was NOT consistent with what would be expected for a gas.

en.wikipedia.org/wiki/John_Snow Image
29/ Snow noticed how cases had clustered in a specific London borough and persuaded the local council to remove the handle of the Broad street water pump, which halted the epidemic.

archive.org/details/b28985…
ph.ucla.edu/epi/snow/snowc…
blog.rtwilson.com/john-snows-cho… Image
30/ However, cholera was already in decline. The Board of Health refused to accept contaminated water, stating:

“we see no reason to adopt this belief [that cholera was water-borne]”

and dismissing Snow's conclusions as mere “suggestions"

google.com/books/edition/…
31/ The Board of Health had strong incentives for rejecting water as the source of cholera. To remove the sources of the miasma (filth), they had spearheaded the effort to build sewers that dumped raw sewage into the Thames, the source of much of London's drinking water...
32/ ...thus effectively helping the spread of cholera. They had much to lose by admitting cholera transmitted through water

[Technology has advanced, but human nature has changed less. @WHO has avoided saying LOUD & CLEAR that #COVIDisAirborne, as their denials helped it spread]
@WHO 33/ Also around 1850, Ignaz Semmelweis in Vienna showed that handwashing greatly reduced deaths by childbed fever in a maternity clinic.

en.wikipedia.org/wiki/Ignaz_Sem… Image
34/ These are some of Semmelweis' data, which would seem worth following up on:

However, his ideas conflicted with established medical and scientific beliefs that STILL described diseases as due to an imbalance of humors triggered by a miasma in the air.

doi.org/10.1556/650.20… Image
35/ However, he was dismissed from his hospital and harassed by Vienna medical community, forced to move to Budapest. There he broke down, was interned and beaten by the guards, and ultimately died from an infected wound

Like Snow, he died years before his theories were accepted
36/ Ironically, Semmelweis' name lives on not only for advances of hand sanitation, but also in “Semmelweis reflex,” which describes the reflex-like tendency to reject new knowledge or evidence when it contradicts established beliefs, norms, or paradigms

en.wikipedia.org/wiki/Semmelwei…
37/ That is especially ironic, as the chief deniers of airborne transmission (John Conly -- chairman of key IPC @WHO committee, Dr. Seto, @DidierPittet,
@CollignonPeter) are handwashing experts...

... following Semmelweis' scientific advances, while forgetting about the reflex
38/ The 2nd half of the 19th Century is a period of rapid progress on disease transmission.

Pasteur and Koch proposed the GERM THEORY of disease. Microscopic germs enter the body and are the cause of many diseases.

en.wikipedia.org/wiki/Germ_theo…

worldcat.org/title/memoire-… ImageImage
39/ Germ theory was NOT accepted overnight.

E.g. experiments by others in which water containing organic matter was boiled in a vessel, but microorganisms still appeared (later shown to be an imperfect seal or insufficient boiling) created controversy:

doi.org/10.1093/jhmas/…
40/ However, by the late 1880s, miasma theory was waning in popularity, and in 1888, the Institut Pasteur was created in Paris, reflecting the ascendancy of germ theory.

pasteur.fr/en/institut-pa…
41/ Florence Nightingale did accept the new ideas of germ theory, in fact before many physicians did.

E.g. in 1882, she wrote:

books.google.com/books?id=dDDcy… Image
42/ Initial results on plant pathogens in 1890s & the identification of bacteriophage in 1917 paved the way for recognition of viruses.

A “golden era” followed, with the identification of the actual microorganisms that cause many infectious diseases.

doi.org/10.1002/bies.2…
43/ The discovery and identification of the organisms causing different diseases did NOT, however, eliminate the great difficulty in conclusively determining the mode by which they transferred from one person to another.

Malaria was still thought to go through the air in 1880
44/ French physician Charles Laveran identified the pathogen responsible for malaria in 1880 (got Nobel Prize in 1907), but the manner of transmission was still thought to be through the air.

doi.org/10.1186/1475-2…
en.wikipedia.org/wiki/Charles_L… Image
45/ American physician A. King proposed that malaria was transmitted by mosquitos, but encountered general skepticism

In 1883, he presented a list of 19 facts supporting m. as vector of malaria

[Reminds me of 10 scientific reasons for #COVIDisAirborne]

en.wikipedia.org/wiki/Albert_Fr… Image
46/ In 1898 British surgeon R. Ross provided definitive evidence:

- confirming the presence of the malarial parasites in mosquitoes
- demonstrating transmission of bird malaria by mosquitoes

World Mosquito day commemorates him

doi.org/10.1186/1475-2…
en.wikipedia.org/wiki/Ronald_Ro… Image
47/ Looking back at period 1850-1900, belief on transmission of many diseases through AIR was still strong

But cholera, malaria, puerperal fever had been shown to transmit OTHERWISE

It was a fluid time. It was debated if air was actually important

onlinelibrary.wiley.com/doi/10.1111/in… Image
48/ In the 1890s, Carl Flügge in Germany set out to disprove the then-dominant transmission theory for tuberculosis, one of the major infectious diseases of the time. Most experts believed that tuberculosis was transmitted when dust of dried sputum that had landed on floors... Image
49/ ...blankets, bowls, & other objects was dispersed into air. In contrast, Flügge thought that it was not DRIED secretions from sick that caused infection, but rather FRESH secretions that ppl were exposed to IN AIR BEFORE they reached the ground

doi.org/10.1098/rsfs.2… Image
50/ Some contemporaries of Flügge such as Cornet argued that tuberculosis was transmitted only through large droplets, which were easily visible to the naked eye.

Perhaps because droplets were more CONVENIENT and airborne disease VERY INCONVENIENT?

google.com/books/edition/… Image
51/ However, although term “Flügge's droplets” has been used to describe ONLY those large particles that fell to the ground quickly near the infected person and that were assumed to dominate transmission, that does NOT accurately capture Flügge's results

journals.sagepub.com/doi/10.1177/00…
52/ Rather, Flügge and collaborators used the term “droplet” to refer to fresh particles of ALL SIZES, including AEROSOLS for which the researchers waited 5 hours to settle from the air on their collection plates.

doi.org/10.1098/rsfs.2…
53/ In 1905, microbiologist M.H. Gordon was commissioned to study the atmospheric hygiene of the UK House of Commons after an epidemic of influenza among members

He famously performed the following experiment: after gargling with a broth culture of Serratia marcescens...
54/ ... he loudly recited passages from Shakespeare in an empty House to an audience of agar plates. Although growth of colonies was more numerous on plates near the speaker, cultures were apparent on some plates over 21 m away.

bmj.com/content/4/5686…
55/ However, experimental progress in early 1900s was hampered by the limitations of the experimental techniques available at the time. In particular high-quality measurements of large droplets & aerosols would only be routinely available decades later.

onlinelibrary.wiley.com/doi/10.1111/in…
56/ We get to the CRITICAL POINT of this history.

Throughout most of human history, the dominant belief was transmission of many diseases through the air.

The last half of the 19th Century proves otherwise for major diseases.

Strong debate ensues: "is air major or minor?" Image
57/ Charles V. Chapin was a prominent American epidemiologist. He worked only a couple of decades after Germ Theory was accepted, during a period of intense research on pathogens & their transmission.

en.wikipedia.org/wiki/Charles_V… Image
58/ The period when Chapin's worked on disease transmission was a fluid one, following a major paradigm shift, in which it was easier to change the dominant scientific discourse than during normal times

[See e.g. Kuhn en.wikipedia.org/wiki/The_Struc…]
59/ He summarized the evidence of transmission of different diseases in his 1910 seminal book, “The Sources and Modes of Infection.”

[A must read if you are interested in this subject, esp. chapter on airborne transmission]

play.google.com/store/books/de… Image
60/ Chapin conceptualized “contact infection,” infection by germs that did NOT come from the environment, but from other PEOPLE through DIRECT CONTACT OR CLOSE PROXIMITY.

play.google.com/books/reader?i… Image
61/ Chapin believed contact was main mode of transmission of many diseases

But he encountered resistance: “I have sometimes been told I lay too much emphasis on contact infection [although] until recently very little attention has been paid to it.”

play.google.com/books/reader?i…
62/ Chapin also reviewed the possibility of airborne infection, which he conceived especially as infections from afar. Lingering belief on air infection was making it difficult to promote contact infection:

play.google.com/books/reader?i… Image
63/ Chapin realized that airborne infection may explain infection in close proximity (CP). However, he argued that ease of infection in CP was better explained by “spray-borne” droplets, large visible droplets considered by Cornet

Same as @WHO's droplets:
64/ This is the key. The evidence was insufficient, but Chapin turned absence of evidence into evidence of absence, and stated that airborne disease was almost impossible, and that "mouth spray" (large droplets) are only effective at short distances.

onlinelibrary.wiley.com/doi/10.1111/in… Image
65/ As we have explained in another recent paper, Chapin conflates an empirical fact ("distance reduces transmission") with a mechanism: GRAVITY, which makes the droplets fall close to the infected person.

doi.org/10.1111/ina.13…
66/ Problem: the more correct explanation (of why distance reduces trans.) is NOT gravity but DILUTION:

Like exhaled smoke, you breathe less exhaled air farther from someone.

And error in PHYSICS made by MEDICAL professionals who do not study physics!

onlinelibrary.wiley.com/doi/10.1111/in… Image
67/ Despite the lack of evidence, Chapin was too successful.

He was much better positioned than Snow or Semmelweis as the long-serving Health Officer of Providence and w/ success of reducing contact transmission iin a new hospital. In 1927, he became President of @PublicHealth
68/ Chapin was described in 1967 as “the greatest American epidemiologist” by A. Langmuir, 1st & long-time director (1949–1969) of epidemiology branch of @CDCgov

As late as the 1980s, Chapin's views were dominant there.

doi.org/10.1093/aje/14…
en.wikipedia.org/wiki/Alexander… Image
69/ CRITICALLY, Chapin's unproven hypothesis was accepted as true:

Ease of infection in close proximity is accepted proof of transmission from sprayed droplets

This KEY ERROR conditioned the evolution of this field over the next century, and into the COVID-19 pandemic
69/ The 1918 flu led to lots of work and discussion in this area, but did not blunt the ascendance of of Chapin's theory:

onlinelibrary.wiley.com/doi/10.1111/in… Image
70/ In the 1930s, Harvard engineering professor William Wells and physician Mildred Wells, his wife, started applying more contemporary experimental methods to the investigation of airborne transmission.

en.wikipedia.org/wiki/William_F… Image
71/ But Chapin had successfully shifted the paradigm and his theory was now viewed as scientific progress.

The Wellses were accused of a retrograde approach to science, which sought to bring back the miasma theory.

jamanetwork.com/journals/jama/… Image
72/ Wells was 1st to rigorously study size of sprayborne droplets vs. airborne aerosols

Conceptualized dichotomy of sprayborne droplets (≳100 μm), reach the ground before drying

Vs. aerosols (≲100 μm), dry before they reach ground ( “droplet nuclei”)

academic.oup.com/aje/article-ab… Image
73/ Wells understood connection w/ meteorology where this is common knowledge, stating:

“A raindrop 2 mm in diameter can fall miles without completely evaporating under conditions which would cause a 0.2 mm droplet to evaporate before it had fallen from the height of a man.” Image
74/ Shockingly, Public Health and Infectious Diseases have published for decades that large droplets are those heavier than 5 microns (!!). Including in the latest @WHO Scientific Brief on COVID Transmission that addresses this issue: Image
@WHO 75/ We pointed out this glaring error many times. I.e. see that even at 50 microns, they don't fall quickly:

Not too important per se, but makes glaringly obvious the ignorance of physics by those in charge at @WHO and its IPC committee.

76/ We investigated the history of the 5 micron / 2 meters error in a previous paper led by @linseymarr and the extraordinary @katierandall, with support from @EThomasEwing, Lydia Bourouiba of @MIT and yours truly:

royalsocietypublishing.org/doi/10.1098/rs…
77/ I am getting slightly out of order. I'll explain the reason for the "5 micron particles fall within the meters of the person" enormous error later in the thread, once I have explained the background.

So we were talking about the work of William Wells on airborne infection.
78/ The Wellses suspected that tuberculosis and measles were airborne, but BOTH were already believed to be droplet diseases, and they encountered intense resistance from the epidemiological community.
79/ Measles was thought to be a droplet/fomite disease. At the time of Wells... and as late as 1985, because of:

- ease of transmission in close proximity (= sprayborne droplets per Chapin)
- cases of lack of infection w/ shared air

pediatrics.aappublications.org/cgi/pmidlookup… Image
80/ Wells thought that measles was airborne (and now we know he was correct, though he died 2 decades before this was accepted)

Wells has some initial success showing that UV lights installed in the ceiling of classrooms greatly reduced measles infection

ajph.aphapublications.org/doi/10.2105/AJ… Image
81/ However, subsequent attempts to replicate these findings produced mixed results.

In retrospect, in schools where UV prevented measles transmission, children were together indoors only in the school, not elsewhere. In other schools, children shared other spaces (e.g. buses)
82/ Wells established the scientific basis of airborne infection

But he was working in a period of intense hostility in public health and inf. diseases towards airborne tr., ushered by the success of the 1910 paradigm shift of Chapin after 2 millenia of belief in miasmas Image
83/ General skepticism against airborne tr. is illustrated by 1951 quote of Langmuir (first and longtime director of epidemiology @CDCgov) :

“It remains to be proved that airborne infection is an important mode of spread of naturally occurring disease"

jstor.org/stable/4587679
84/ Langmuir worked preventing disease trans. among US military in WW II

Substantial resources were dedicated to the effort, generating knowledge “which would have taken decades to accumulate under peacetime conditions” & established leaders for decades

doi.org/10.1093/aje/14…
85/ Langmuir et al. studied airborne transmission, but MISINTERPRETED the results of their own studies:

Distance reduced transmission, therefore it was droplets. Ignoring that distance reduces airborne transmission by dilution.

doi.org/10.1093/aje/14…
doi.org/10.1111/ina.13… Image
86/ However, Langmuir's work renewed interest in airborne infection, as he concluded that WEAPONS of airborne disease could be created, which became a topic of intense interest during the cold war.

jstor.org/stable/4587679
87/ Despite stubborn resistance to the idea that airborne transmission had relevance for natural diseases, Wells, Robert Riley [pic] & Cretyl Mills succeeded in demonstrating airborne transmission of tuberculosis (TB) in 1962 through extensive efforts

doi.org/10.1164/arrd.1… Image
88/ They routed air from TB hospital ward to 150 guinea pigs (GP) for 2 yrs. ~3 GP / month were infected

No GP infected in control group where the only difference was that the air was irradiated with germicidal ultraviolet light, killing the TB bacterium

doi.org/10.1164/ajrccm… Image
89/ Because of this, TB was the first important natural disease to be accepted as airborne in modern times

It was shown that pulmonary TB can ONLY infect if bacterium-containing aerosols reach the alveoli, for which they need to be smaller than 5 microns

epa.gov/pmcourse/parti… Image
90/ Here is when we think that the ERROR of "5 micron particles fall to the ground in 1-2 m" originated:

Only TB and bioweapons were important, someone at @CDCgov confused the size that goes to alveoli with size that falls to ground

Repeated till 2020

royalsocietypublishing.org/doi/10.1098/rs…
91/ The fascinating story of how @katierandall, @linseymarr et al. figured out the cause of the 5 micron error was told in this article in @WIRED by @MeganMolteni.

Reads like a spy novel, one of the best of the pandemic!

wired.com/story/the-teen…
92/ In paper we characterize the years after the demonstration of TB as "Reluctant acceptance of as little airborne transmission as possible (1962–2020)"

Airborne disease was not impossible, but required an extremely high (undeniable) standard of proof.

onlinelibrary.wiley.com/doi/10.1111/in…
93/ Unfortunately, standards of evidence were v. different for different routes of trans.

Many diseases accepted as “droplet” w/o any substantive proof—let alone extensive and time-consuming experiments

Only the hypothesis of Chapin, ease of infection in close prox. = droplets
94/ Remember, large droplet transmission has NEVER been demonstrated DIRECTLY for ANY disease in the entire history of medicine

[Paper from Prof. Yuguo Li, lone airborne specialist in @WHO IPC Committee]

sciencedirect.com/science/articl… Image
95/ An example of the resistance to airborne: an obvious case of long-distance airborne transmission of smallpox in Germany in 1970.

SP airborne trans. debated for centuries, only definitely accepted in the complete absence of community transmission

pubmed.ncbi.nlm.nih.gov/5313258/ Image
96/ An infected person arrived from Pakistan to Germany, where there were no cases at all.

Only possible explanation was transmission through air. In latter tests, smoke from index case room went to rooms of secondary cases.

academic.oup.com/aje/article-ab…
pubmed.ncbi.nlm.nih.gov/5313258/ Image
97/ The case report shows the prevailing bias against airborne in Public Health:

“The only remaining route of transmission considered reasonable was airborne spread of a virus-containing aerosol, **a possibility against which all of the investigators were initially prejudiced**”
98/ Measles and chickenpox were similar, described as droplet diseases till mid-1980s, and only accepted when superspreading events with long-distance transmission made airborne undeniable.

publications.aap.org/pediatrics/art…
nejm.org/doi/full/10.10… Image
99/ Interestingly the @WHO IPC commitee members stated that COVID could not be airborne as it was much less transmissible than measles. Otherwise they would have recognized it quickly

Except... it took their profession 70 years to recognize it...

aricjournal.biomedcentral.com/articles/10.11…
100/ Note that it is always the same error, going back to Chapin.

Assuming that ease of transmission in close proximity (and decreasing transmission w/ distance) is proof of large droplets, and that airborne is very unlikely.

For TB, measles, chickenpox... and COVID-19
101/ SARS-1 in 2003 brought renewed attention to airborne transmission

Superspreading was clearly observed. Airborne spread was implicated in several outbreaks in hospitals, and also in large Amoy Gardens outbreak in Hong Kong

doi.org/10.3201/eid100…
doi.org/10.1111/j.1600…
102/ Same dynamic played out for SARS-1:

- observed ease of infection in close proximity was considered evidence of droplet transmission

- airborne transmission was considered unlikely, and only accepted if evidence was undeniable

From IPC member:

sciencedirect.com/science/articl…
103/ During last several decades, until the COVID-19 pandemic, with available antibiotics, vaccines, and no major respiratory pandemics, studies further probing the details of droplet vs. airborne transmission had NOT been a major public health priority.

onlinelibrary.wiley.com/doi/10.1111/in…
104/ High standards of ventilation & filtration ain modern hospitals mean that airborne risks have been substantially mitigated in these settings, where many key infection control scientists work.

cdc.gov/infectioncontr…
techstreet.com/ashrae/standar….
105/ Adherents of droplet transmission were in control of all key public health institutions.

Scientists proposing airborne transmission were typically ignored (as we saw later for COVID-19, and explaining persistence of errors)

royalsocietypublishing.org/doi/10.1098/rs…
wellcomeopenresearch.org/articles/6-126…
106/ This schematic qualitatively captures the situation before COVID-19 appeared:

onlinelibrary.wiley.com/doi/10.1111/in… Image
108/ Importantly, substantial scientific evidence had accumulated (BEFORE COVID) of airborne transmission of the flu, as reviewed in this paper in @ScienceMagazine (led by @ChiaWang8 and @kprather88):

science.org/doi/10.1126/sc… Image
109/ But the evidence of airborne transmission of the flu had been ignored, and @WHO and @CDCgov pages on the flu ONLY mention droplets & surfaces

who.int/news-room/fact…
cdc.gov/flu/about/dise… Image
110/ Airborne transmission is well accepted in veterinary medicine, including several coronaviruses and flu viruses.

And sometimes over many kilometers (facilitated by large animal concentrations)

Every veterinary I've talked to is dismayed about COVID

onlinelibrary.wiley.com/doi/10.1111/in… Image
111/ Finally we get to the COVID-19 pandemic. It is so massive and disruptive that every researcher that can contribute in some way gets to work doing so.

Includes lots of aerosol researchers (e.g. yours truly), with fast collaboration with medical researchers, virologists etc.
112/ Some early scientific and public health reports out of China state that COVID-19 has airborne transmission:

doi.org/10.1038/s41586…
bbc.com/zhongwen/simp/…
113/ Despite a lack of direct evidence in favor of droplet or fomite transmission of COVID, by Mar 2020 @WHO concluded that ease of transmission in close proximity proved that COVID-19 was transmitted by those mechanisms, continuing Chapin's 1910 error

114/ The same errors described for other diseases are repeated for COVID-19. And the bar is moved higher: unlike TB, animal transmission is not enough. Unlike measles, superspreading and long-distance transmission is not enough...

onlinelibrary.wiley.com/doi/10.1111/in… Image
115/ However, accumulating evidence in favor of airborne, and critical LACK of evidence for droplets or surfaces tilts the balance

Airborne transmission is (reluctantly and slowly) accepted.

E.g. one summary of evidence for #COVIDisAirborne:

116/ @WHO commissioned some reviews on the modes of transmission of COVID-19. The one on airborne included no airborne experts, and has been rejected by the reviewers:

f1000research.com/articles/10-23… Image
116/ Shockingly, no review has appeared (to my knowledge) on the evidence in favor of large droplet transmission, despite @WHO being so sure for a long time that it was dominant.
117/ A @WHO-sponsored review has been written on "close contact transmission" == "close proximity".

But that is a measurement of distance, NOT a mechanism of transmission!

Still carrying the error of Chapin, confusing close proximity w/ spray droplets

f1000research.com/articles/10-280
118/ That @WHO-sponsored review on close prox. transmission has also NOT been accepted for publ., and remains in limbo after over a year

Even though THEY GET TO CHOOSE REVIEWERS!

Read the comments that we posted on both articles:

f1000research.com/articles/10-280
f1000research.com/articles/10-23…
119/ "Aerosol-generating medical procedures" were the only accepted cause of airborne transmission for over a year (e.g. by @WHO).

They originated from low-quality research in SARS-1. Research has show that real AGPs are talking, singing...

onlinelibrary.wiley.com/doi/10.1111/in… Image
120/ @WHO has finally accepted airborne transmission, including the fact that transmission in close proximity includes short-range airborne transmission.

But only in Dec. 2021, after we pushed them a lot. Image
121/ But both @WHO and @CDCgov communicate poorly about this, not explaining it to the public, and avoiding the word "airborne" (which is the clearest for the public) as much as they can

E.g. no mention of airborne COVID in @WHO's extensive Twitter feed:

twitter.com/search?q=airbo…
122/ And especially no clear description of the control measures. As @kprather88 keeps saying, it is totally doable to majorly reduce transmission, once we accept it and get serious about it.

But it is a really inconvenient truth for those in power...

123/ My pinned tweet has a good summary of those protection measures against transmission (also in many other sources such as @CleanAirCrewOrg, or the @CDCgov web pages if you actually read them in detail):

123/ So where does that leave us in mid-2022:

- PH institutions such as @CDCgov have given up on explaining or preventing transmission. Too inconvenient for those in power

- Scientifically, cat is out of bag. Tons of evidence of airborne, some medical & PH ppl understand it
124/ - Measures to improve ventilation are favored (e.g. by the @WhiteHouse) since they don't face resistance from public, but they are inconsistently applied.

- CO2 meters are resisted by institutions, because they make poor ventilation obvious.

whitehouse.gov/ostp/news-upda… Image
125/ Not sure how this will evolve. But as it becomes scientifically clearer, it will be harder to justify lack of action

But as we know from climate change (follow twitter.com/i/lists/105306…), the sci. evidence can be overwhelming & those in power still resist inconvenient actions
126/ This is the final (hopeful) paragraph of this historical paper.

Wells lamented in 1945 the ignorance of airborne transmission in PH (jstor.org/stable/18316#m…)

Let's hope that ends with COVID-19 (& fight to make it reality - we need to be activists)

onlinelibrary.wiley.com/doi/10.1111/in… Image
127/ I didn't do this alone. I got involved in COVID-19 transmission research in early 2020, and was shocked and confused by the stubborn and impatient resistance we faced.

E.g. Conly's (@WHO IPC Chair) rudeness on our Apr. 2020 call w/ @WHO]

wired.com/story/the-teen… Image
128/ I've been lucky to work with the Morawska/@Don_Milton group of 36 scientists & with many others

@Don_Milton made me curious about history, mentioning Chapin and his impact. I was perplexed an "ancient" researcher could influence @WHO advisors today so much. Started reading
129/ As we investigated many aspects of transmission, I kept an eye on the history. The paper on the 5 micron error with @katierandall and @linseymarr made me learn a lot, and also see more clearly the pendulum of history: Image
130/ Contributors to the paper include @linseymarr @katierandall @EThomasEwing @zeynep @trishgreenhalgh Raymond Tellier, Julian Tang, Yuguo Li, Lidia Morawska, @jmcrookston @DFisman @Orla_Hegarty Stephanie Dancer, Philo Bluyssen, Giorgio Buonanno, @Marcel_Loomans @WBahnfleth...
131/ [Authors continued] @pkubioaerosol Chandra Shekhar @WargockiPawel Arsen Kritov Melikov and @kprather88

The authors contributed majorly to the paper. If there are any remaining mistakes, they are mine.
132/ As always, if you think that something is incorrect, or if you have a paper that contradicts (or further supports) anything I am saying here or in the paper, please send it my way
133/ My apologies that I have been pretty absent from Twitter for several months. We have had a bit of travel, and had a major field study this summer and that consumed a lot of bandwidth. Image
134/ Thanks to @kprather88 this history paper has an illustrious reader on Dr. Fauci.

135/ Someone asked about why we did not cover the understanding of transmission in East Asia.

We were curious about it, also in Eastern Europe during cold war, both seemed more favorable to airborne.

There is clearly material for many papers there (send me any you find)
136/ But in investigating the history, it seemed that the denial and resistance of #COVIDisAirborne, led by @WHO and @CDCgov, was rooted in Western science and the Chapin error. So we focused on that in this paper.

See this text on paper (Methods):

onlinelibrary.wiley.com/doi/10.1111/in… Image
137/ There is an important typo on tweet #122.

The @WhiteHouse document came out in Mar-2022, NOT 2020 as the slide erroneously showed (things could have been very different in that case! ALthough @CDCgov has just ignored this @WhiteHouse doc)

Thxto Lin & @kprather88 for catch Image
138/ When the American Thoracic Society is re-tweeting our work, I have hope that change may come

Change on airborne trans. will NOT happen (or REALLY slow) unless medicine / public health pushes

Thanks @atscommunity! [& Understood RT is NOT endorsement]
139/ BTW I forgot to thank @numeroteca for lots of help with the key figure on the paper (below)

And other Twitter users that helped me polish it online on this thread: (& another I can't find) Image
140/ I wrote SHORTER thread explaining larger picture of REASONS FOR RESISTANCE AND DENIAL OF #COVIDisAirborne by @WHO @CDCgov @sanidadgob & PH, governments, & corporations in general

TDLR: history set us up, but key: AIRBORNE IS INCONVENIENT TO POWER

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More from @jljcolorado

Prof. Jose-Luis Jimenez Profile picture
May 8
1/ "After four years of fighting about it, @WHO has finally proclaimed that viruses, including the SARS-CoV-2 virus that causes COVID, can be spread through the air"



By @maggiemfoxscientificamerican.com/article/a-figh…
2/ "It took four years to get here because some leaders in public health, medicine and science clung too tightly to precision and semantics"

"One particular moment of shame came on March 28, 2020, when WHO tweeted: “FACT: #COVID19 is NOT airborne.”

3/ "Words matter. When people heard that COVID might spread on surfaces, they wasted time wiping down groceries. People who misunderstood airborne spread needlessly wore masks on outdoor walks and veered off sidewalks to avoid their neighbors."
Read 7 tweets
Prof. Jose-Luis Jimenez Profile picture
Apr 18
1/ @WHO has published a report on updated terminology for disease transmission

I've seen some debate about it. My take:

- Terminology itself is ok. Big progress
- But no recommendations of how to protect!

Report:

Press release: who.int/publications/m…
who.int/news/item/18-0…
2/ The report was likely the result of intense pressure on @WHO during the pandemic:

- They denied that #COVIDIsAirborne on March 2020
- They finally accepted it 2 years later

nature.com/articles/d4158…
@WHO 3/ To their credit, @WHO did invite some of their critics to be part of the committee.

What was the terminology before. In medical circles:

- droplet transmission: if it happened in close proximity, or if particles were > 5 microns

- airborne transmission: if it happened far
Read 34 tweets
Prof. Jose-Luis Jimenez Profile picture
Mar 28
1/ New paper in @ScienceMagazine: "Mandating Indoor Air Quality for Public Buildings"

Explaining current status of indoor air quality standards (in short: bad or non-existent), the huge health benefits that would arise from them & proposing a path forward
science.org/doi/10.1126/sc…
Image
2/ "People living in urban & industrialized societies, which are expanding globally, spend more than 90% of time indoors, breathing indoor air (IA)."

"Most countries do NOT have legislated indoor air quality (IAQ) performance standards for public spaces"

science.org/doi/10.1126/sc…
3/ "Few building codes address operation, maintenance, and retrofitting, and most do NOT focus on airborne disease transmission."

"We propose that Indoor Air Quality (IAQ) standards be mandatory for public spaces"

science.org/doi/10.1126/sc…
Read 14 tweets
Prof. Jose-Luis Jimenez Profile picture
Oct 4, 2023
1/ Checking the ventilation by measuring CO2 as I travel to the #AAAR2023 conference

@RideRTD bus to Denver airport. Bus route had started 3 min before I got in, already 1500 ppm

Typical of these @RideRTD buses, poor ventilation Image
2/ Not getting any better as time passes in the @rideRTD bus to the airport...

7% of the air is being re-breathed, it has already been in someone else lungs when each of us breathe it. Image
@RideRTD 3/ Given the often poor-to-mediocre ventilation in US transportation systems, I wear N95 masks (not KN95, less good)

In this case @3M VFlex, which I tested at 99.99% filtration for myself

It also stays sealed when I talk, doesn't distort my speech (& add to my Spanish accent) Image
Read 14 tweets
Prof. Jose-Luis Jimenez Profile picture
Oct 2, 2023
1/ Video de mi presentación sobre "Transmisión de enfermedades por el aire: cómo funciona, por qué se malentendió, y cómo reducirla"

como parte de la presentación del libro de ventilación de @aireamos

2/ Las diapositivas se pueden bajar de este enlace.

(Son de una charla más larga así que tienen más detalles, pero están todas las de la presentación de @Aireamos)

drive.google.com/file/d/1Bs0RRG…
@aireamos 3/ Miguel Ángel Campano @MA_Campano y @Aireamos han sido los motores del libro de ventilación:

Read 4 tweets
Prof. Jose-Luis Jimenez Profile picture
Sep 1, 2023
1/ Measuring CO2 indoors in a 10 day trip from US to Europe & back

Bus @RideRTD to Denver airport, poorly ventilated as usual.

We have not left town yet! In previous trips it kept increasing, we'll see this time. Image
2/ For background on what CO2 indoors indicates and more details, see

TLDR:
- We exhale 40000 ppm CO2
- Outdoors: 420
- Each 400 extra ppm indoors = 1% extra rebreathed air
- CO2 makes us dumber, indicator of virus & pollutants. Does not capture filteringdocs.google.com/document/d/e/2…
3/ Or by reducing recirculation. Some recirculation is ok if well-filtered, saves energy.

Energy-recovery ventilators allow ventilating well with limited energy use.

Read 18 tweets

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