Daniel Lakeland writes:
This news article by Megan Molteni seems like an article that’s got it all for the blog:
1) A physics based estimate from a lifetime ago, that was ignored
2) A dogma that was established and was enormously harder to debunk than it was to originally be established
3) Both physicists and physicians who for decades have fought the established dogma
4) A historian who cracks how the mistaken dogma got established
5) The pandemic, and indoors vs outdoors transmission
6) Still probably the 5 micron error persists but CDC/etc just pretend that COVID spreads in 5 micron droplets
Phil adds:
I saw this article and barely believed it, it seems so ridiculous. “Aerosol science” is a thing, it’s not like it needed to be invented for the pandemic. You can look up aerosol settling times by diameter just by searching online. And, hey, at least for me, one of the top hits is a cdc presentation that has a good qualitative and semi-quantitative description! It’s sort of incredible that it was such a battle to get so many people to pay attention to facts that were so well known and well documented.
Here’s the TL;DR summary on this one. The details are in the long-form Wired article linked by Andrew:
When I wrote this I had been talking with a friend about doing simulations of falling times of different particles as a way to communicate what the range of “aerosol” particles was. It’s not like I thought we were the first people to think of doing that, but reading in the news constantly that “aerosols are 5um or smaller” was driving me crazy! When I was a TA in grad school I created a project for the intro to programming in Matlab class I was TAing where we would use an empirical formula for the drag coefficient for a sphere and matlab’s numerical ODE solvers to simulate the flight of spherical objects through the air and plot them. It was quite obvious to me that objects larger than 5um could stay in the air for a long time. (it’s also very interesting to see how what Aristotle thought about motion of projectiles was actually basically down to not neglecting air-drag)
In the end, doctors conflated two things:
1) Hang-time in the air vs
2) Access to deep lung tissues
Yes, the respiratory tract will filter out a lot of larger particles in the upper airways, so if you’re trying to spread **tuberculosis** via aerosols, it’s only the very small particles that matter, because tuberculosis has to get access to deep lung tissue to infect. It turns out that tuberculosis was the first identified “spread by aerosols” infection, and kinda the last… because it induced this error.
If you’re spreading a respiratory virus that infects in the nose, throat, or bronchus then 100um is still an “infective aerosol”. A particle that size can easily hang in the air for minutes to hours if it’s stirred every few minutes. Like for example an elevator. Just the action of people getting on and off will stir up the air enough that maybe 100um particles can stay in the air for hours.
This is a fascinating story for sure, and very much worth sharing. My thanks for doing so! But because the article focused so much on the current players, I never got a good sense of why the original 5 micron error occurred and persisted for so long.
The origins of the error sound like they were with the Wells’ research and its dismissal by people like Langmuir in the mid 20th century. Obviously those people are dead and couldn’t be interviewed, but surely there are people around who knew them or contemporaneous writings that could have shed more light on why the original research was so grossly misinterpreted and/or ignored.
Moreover, the article claims that Langmuir’s opinions changed based on later research by Wells. But then why didn’t the opinions of the public health establishment change too? Did no one else try to correct the record? Was there no other research that could have challenged this idea?
Finally, if Randall’s hypothesis is correct that the 5 micron thing was just a conflation based on the size of tuberculosis particles, who can we ask to see if this is true?
I suspect it’s similar to the NHST/p value situation, or the “undrained soil” explanation for earthquake liquefaction (the myth that I busted in my PhD). Once you enshrine a simple but wrong idea into the textbooks and lectures in a field, it persists for decades or centuries because too few question it. Medical students have about a billion things to learn, so they learn these really simplified stories that are not based on science but rather mnemonics. “Aerosols are 5um or smaller, and most diseases aren’t transmitted that way, Tuberculosis is an example exception” is pretty simple to remember. It’s also very wrong. Even people at the CDC know it’s wrong. After all you can google around and find some nice slides at the CDC that explicitly have it right! But a few people who know what they’re talking about are no match for an army of badly-educated “experts” who will shoot them down out of “expert knowledge” of the ignorant dogma from med school.
I’m sure a lot of people here are familiar with the idea. For example how strangely would a medical researcher look at you if you told them “p values are bogus, and probability doesn’t mean the long run frequency of an observation, let’s build a bayesian model of your process, what’s your prior knowledge of the infection rate among children in a daycare setting?”
Agreed that this seems like another example of the inertia that needs to be overcome to correct a widely-held error. Even when there is little-to-no reason to persist in believing the error.
But that’s why I was hoping the article would delve more deeply. As it is, the story seems to boil down to “shit happens.” Of course this is true, but not as enlightening as I would have hoped. And who knows, maybe that’s really all that can be said in this instance?
A “60-year-old scientific screwup that helped Covid kill”? Ha – we statisticians have got that beat. How about a 90+ year screw-up that helped Covid kill – namely, the mis-interpretation of statistical significance in the assessment of what works/doesn’t work in protecting against/treating Covid ?
Sure. Never seen anything like it in science.
/sarcasm.
Andrew –
Should there be a 7 on your list?
It may not be entirely shocking that in that story women may have been disproportionately represented among those having trouble being heard, or that (as my “wife” points out), aksd if so part of the reason might be that their outside the box thinking may have been influenced, in part, from observing daycare.
I wonder how much the droplet-aerosol dichotomy was supported by the information from R&D about inhalers (inhaled medications for asthma/copd). We were/are taught that droplet size is key, too big and the medication settles out in the mouth allowing absorption of (larger amounts) of medication that would produce only side effects, too small and you breath it in and then out again and just-right it would settle out in the alveoli where it can reach the target efficiently. That kind of simple explanatory framework maybe makes sense for inhalers where the system is arguably less complex (usually there aren’t breezes or ventilation interfering with an administration of an inhaler puff). But it is also a nice simple explanatory framework for thinking about droplets and easy to make the mistake of generalizing it to other settings. It is hard to remember everything even in a field where you have some expertise so very easy to grasp and hold onto simple explanations that seem to make sense and facilitate information retrieval.
Alas the article is interesting and all too familiar. It is not at all unusual for incorrect or over-simplified dogma’s to become established in medicine (or most fields I expect). As someone who has spent a long time teaching clinical medicine I can think of many other examples. After they are finally debunked they become useful teaching points but those who didn’t experience the lure of a comfortable explanation usually smile sympathetically and think that they would not have been susceptible.
I find this quote still relevant even though it reflects on the late 19th century.
“For, medicine being a compendium of the successive and contradictory mistakes of doctors, even when we call in the best of them the chances are that we may be staking our hopes on some medical theory that will be proved false in a few years. So that to believe in medicine would be utter madness, were it not still a greater madness not to believe in it, for from this accumulation of errors a few valid theories have emerged in the long run.”
Really interesting. This earlier article from the NY Times, linked in the above article, is also worth reading. When I read it a few weeks ago I wondered how long it would take to make it to this blog. https://www.nytimes.com/2021/05/07/opinion/coronavirus-airborne-transmission.html
I would add a “(7) Example of “Evidence based medicine” ignoring evidence and demanding a published study instead.
When I first read that infectious disease experts were debating whether COVID was spread by droplets and therefore not airbourne, I was stunned. I have pollen allergies. Pollen is way bigger than 5 microns. How did these experts square that with there belief that droplets can’t become airbourne? It reminds me of the mask debate. We’ve known for more than a century that the use of surgical masks prevent the spread of infections. Why would masks suddenly be different with dealing with COVID? “Evidence based” has become a statistically significant finding in a published study even when we can easily extrapolate from existing evidence to a simple conclusion.
The “evidence” in “Evidence Based” was twisted into a weird pseudo-technical term-of-art by that “EBM” movement. You could smell it early on, twenty some years ago; when someone would ask you if you’d “heard of EBM?” and you might say, well, “that sounds like a fine alternative — as opposed to the alternative [which would be what, “MSE”, Medicine-sans-Evidence ?]” And the joke would be met with an uncomprehending frown — the humourless mien of the dead-serious proselytizer, and one with an especially complicated package of goods to be sold too!
I remembering seeing an EBM hierachy of studies with RCTs on top and all the other observational studies below in descending order and thinking that means Darwin and Newton had pretty weak evidence as most of it was just observational.
In all fairness, I saw plenty of “experts” saying early on that the boundary between “droplets” and “aerosolized particles” was pretty arbitrary.
There are reasons besides mere incompetence and intransigence that public health agencies are typically conservative about redesigning public health recommendations.
That’s not offered as an excuse or to say that incompetence and intransigence don’t exist, but just that “it’s complicated.”
I don’t think it was incompetence at all. The issue was precisely “competence.” With respect to the WHO, they just wouldn’t say the disease was airbourne based on what physicists who studied airpolution were saying. What do air polution experts know about infectious diseases? Ultimately, the WHO is a bureaucracy and a bureaucrat needs an institutional justification for making a call not just a scientific one. Ideally, the U.S. should have empanelled a team of scientists to issue a report and petition the WHO to force the WHO’s hand. Instead, we had random scientists trying to change the WHO’s guidance. If the WHO listened and got it wrong, they wouldn’t have much cover. But, we didn’t exactly have the keenist minds in charge at the time.
I sensed, too, at the time — but maybe this was psychological projection so to speak — that a lot of that tendency was “whistling past the graveyard”: the experts were just as terrified of the possibilities as the meeker among the rest of us. They just found a somewhat sophisticated way to split hairs; but it was, in the truest sense, wishful thinking!
I agree.
“What do air polution experts know about infectious diseases?” Sorry, but if the WHO doesn’t understand the air pollution scientists/engineers are the foremost experts on understanding particulate matter and its suspension in the air, then they are fools.
For more details of aerosol transmission and much else, see “FAQs on Protecting Yourself from COVID-19 Aerosol Transmission” at https://tinyurl.com/FAQ-aerosols Linsey Marr is one of the authors of this.
No wait! This is the link I like! Thanks! :)
This writeup is great, but is there anything more recent from this group, or anything similar? Eight months is a long time — for instance, fomites are still a live option in this analysis.
It’s clear that fomites are an option. There are at least two contact tracing events that identified fomite transmission that I know of. One was a garbage can lid, another was frozen foods.
It’s clear that fomites are not the major transmission route but they also aren’t zero risk.
I think of aerosols in terms of smoke and aerosols, which have a long history of military usage:
https://en.wikipedia.org/wiki/Smoke_screen
Great link thanks!
“Li’s elegant simulations showed that when a person coughed or sneezed, the heavy droplets were too few and the targets—an open mouth, nostrils, eyes—too small to account for much infection. ”
That’s almost exactly what I said on here nearly a year ago!! I suggested several times that people conduct physical modelling of how exactly droplets would spread a virus in a large gathering.
“Li’s team had concluded, therefore, that the public health establishment had it backward and that most colds, flu, and other respiratory illnesses must spread through aerosols instead. ”
And this is the same conclusion I came to – albeit with much more limited evidence. The spread of colds and flu is just way to fast to be accomplished by droplets and touch. These forms of transmission would be too slow to infect entire societies over days and weeks.
What’s amazing is that an epidemiology amateur like myself can read that evidence so quickly while thousands of professionals in the field deny it
It’s frustrating that you can’t trust the experts on a lot of things, and that it’s hard to separate those things from the things where you can trust the experts. Doctors are supposedly told at the start of med school that “half of what you learn will be wrong; the problem is, we don’t know which half”, but they don’t really believe it…which is good, because it isn’t true. Maybe 5% of what they learn is wrong, and they don’t know which 5% but it’s not like the candidate list includes the whole corpus (ahem). There’s not really a question about what the liver does, or what a healthy blood oxygen level is.
The vast majority of the time, when someone says they know better than the experts, they’re wrong. People often think phenomena are simpler than they are, and sometimes think they’re more complicated than they are. People apply lousy heuristics, they make incorrect judgements from small or bad samples, they assume their personal experience generalizes more than it does, etc., etc. If I have to choose between what Joe Schmoe is saying and what an expert is saying about something, I’ll go with the expert.
But then you have these occasional cases where experts have something wrong for decades. They all track back to people believing what they were taught in grad school, which turns out to have been taught as fact when it actually was not fully proven. But until someone goes back and checks, it can be hard to separate the well-supported assertions from the poorly-supported ones.
The whole phenomenon, which occurs to some degree in most areas of science, makes it hard to calibrate one’s skepticism. Believing all expertise is nonsense and you should just judge things for yourself is absurd — which doesn’t stop lots of people from operating that way! — but if you believe everything the experts say then you’re a chump.
Further: I may be rightfully skeptical about the direction being taken on advice of the experts; I may stay up all hours and write irritated and irritating letters to experts and politicians and web discussions. I may be right; I may be wrong. But suppose were they to knock on my door the following day by some possibility and say, “All right wiseguy; *you’re* in the drivers seat today; *you* make the damn decisions!” Would I really be psychologically sound and able and for that matter would I be *willing* to take on the responsibility?
I won’t post the link for fear of getting stuck in moderation but you can find online a superb January 2021 essay on this topic by Alvaro De Menard called “Are Experts Real?” (Answer: pretty much what Phil said.)
Should’ve stuck with the chess player comparison. In fact physicists are among the very worst offenders when it comes to not understanding – being ignorant of – some material foundational to their field.
Changed my mind, then. Experts aren’t real.
This is over a year old but still makes for interesting, unsettling reading:
https://www.washingtonpost.com/health/2020/06/16/coronavirus-toilet-flushing/
“For all our paranoia about the surface of toilet seats — the tissue paper we oh-so-carefully lay down, the thin covers often offered in public stalls — germ transmission from skin contact is a relatively small health risk compared with what happens after you flush. That’s when bits of fecal matter swish around so violently that they can be propelled into the air, become aerosolized and then settle on the surroundings.
Experts call it the ‘toilet plume.’”
This article, aiming at a mass audience, organizes itself around a human interest story, the struggle of underappreciated (often female) scientists to be taken seriously by the public health establishment and the search for the primal error at the heart of it all.
As a social scientist, though, I’m looking for an explanation for *why* the WHO and CDC resisted the aerosol approach even though the logic and evidence were so indicative. The article doesn’t really get at that, or if it does only indirectly. The centrality of TB to the error is recognized, but why was TB given such a distinctive institutional treatment?
Just in passing, the article refers to my favorite hypothesis, that identification of aerosol transmission requires the use of isolation wards dedicated to the disease(s) in question. This is resource intensive. If the primary goal of “public health” is to reduce the demand on these resources one route is reducing the spread of such diseases but the other could be to cordon off as small a set of such diseases as possible. Don’t make hospitals set up isolation wards unnecessarily! It’s not hard to see how small errors or exaggerations in the research record could solidify into hard distinctions that had the effect of defining most diseases as not needing the costly aerosol treatment. TB simply had to be recognized as transmitted by aerosol — there was no choice — but it became established as an exemplary exception. 5 microns, which derived from the particular requirement for TB infection, was established as the demarcation for purposes of identifying when isolation was called for. Interestingly, biological warfare modeling went in the same direction.
Again, this reading is speculative. But the story of encrusted error in public health is not just a matter of intellectual history; it needs an explanation based on institutions and interests.
Yours is not the first comment I’ve read suggesting that one can explain CDC’s behavior by positing that the agency has historically thought of its primary audience as hospitals and clinicians rather than the public, which seems plausible.
Peter –
As to the answer of “Why?,” and as you allude to but in I think maybe a less direct way, over the past few decades public health has been largely defunded (or at least less funded relative to the growth of our economy) – and as such it isn’t so much the institutions and interests associated with public health per se, but institutions and interests at more of a societal level, that might be at the root of the problem.
My own bias is that as a society we tend to go hunting for institutions or personalities to finger for responsibility because they’re easy targets when in fact, the disfunction is broader; our cognitive biases, the influence of social media and other technological changes more generally, and perhaps failures to adapt in our collective politics and approach to civil society.
I fear that the tendency to hunt easily identifiable villains will only recursively exacerbate the larger-scale problems, for example by leading to even less funding of public health in the future.
We can see this more generally with our inability to deal with complex problems like climate change. It’s distressing that, it seems to me, this pandemic has only further illustrated that the fault lines in our large-scale problems are even further undermining our ability to take collective action.
+1
Ditto
In searching for a why, I’m not necessarily searching for villains. In fact, I’m generally a structuralist about these things, and that’s why I mentioned institutions and interests. Of course, individuals in key positions can make a big difference, but at a first pass I would always look for structural explanations.
I agree we need a lot more funding in public health, but a reorientation of the field would also be a good thing. It’s no surprise when an institution’s intermediate goal evolves to become an end in itself. In fact, pushing against that is one of the core tasks of enlightened management. I can understand why reducing the demand on hospital resources would be an important intermediate goal of any public health entity, just as I can understand the logic behind many other public health commitments that I have tangled with over the years. It’s when they become routine and unbudgeable, anchored in conventional wisdom, that problems arise. The description of the conference call between WHO officials and aerosol scientists sounds like such an impasse. (I’ve been in similar situations around occupational health.) Money alone won’t solve this, but of course neither will underfunding these overburdened agencies.
Peter –
Apologies…I didn’t mean to imply that you’re looking for a villain…was just saying that I feel like that’s a general trend these days. And it bugs me, so I’m just kind of venting. I worry that the overall trend is in the wrong direction, which may lead to further disintegration of the viability of public health institutions. Yes, as you speak to there are certainly structural problems, perverse incentives and the like but I think in general there’s too much focus on them, or on bickering about individuals (e.g., Fauci or even someone like Atlas).
My general feeling is we’d be better off with more recognition of the inherent challenges in the public health space. I think we’re probably better off than we’ve ever been when facing a problem such as what’s presented with COVID, but there’s so much hand-wringing. I think it’s reflective of a sense of entitlement. People have a hard time integrating the need to improve along with an appreciation for the benefits we have. In a funny way, I think it connects to the general hard-wired human difficulty with conditional probability. It’s well described when public health officials describe how they’re damned if there’s illness and death (because they didn’t do enough) and also if there isn’t (because they did too much).
I’m curious if you’ve seen any signs of structural reorientation of the sort you suggest.
Joshua —
I’m not angry at individuals (for the most part), but it frustrates me when obstinacy gets in the way of an effective public health response. The article is about aerosols, but we went through this with masking and travel too. Poor communication with the public has not made dispelling disinformation any easier. I like what Zeynep Tufekci has written on this.
As for the hypothesis that much of the public health apparatus has prioritized protection of health care delivery resources at the expense of other objectives, that appears to be a common thread to the snafus. (Masks had to be dissed because health care providers needed them; medical specialists needed to travel freely, and international supply chains had to be sustained for devices and pharmaceuticals; Covid transmission couldn’t be aerosol because that would have costly consequences for hospitals.) That doesn’t prove anything of course, but it does make me suspicious.
I suppose I’m predisposed to think this way because I’ve had interactions in the past with WHO (and a bit with NIOSH) on occupational safety and health that left me feeling the default public health stance was what you might call over-medicalized. That’s not exactly the same as elevating the protection of hospital resources to a primary policy objective, but it’s related. I’ll be the first to admit that my view is rather impressionistic and would need a lot of data and analysis to qualify as a plausible explanation.
“common thread to the snafus. (Masks had to be dissed because health care providers needed them; medical specialists needed to travel freely, and international supply chains had to be sustained for devices and pharmaceuticals; Covid transmission couldn’t be aerosol because that would have costly consequences for hospitals.)”
The common thread can just as well attributed to: [1] wishful thinking in the face of fright; and [2] the tendency to look for the keys under the streetlamp, because that is where the light is; [3] the pale wan substitutions which pass for “leadership” — shocking but probably not at all surprising — in the event. In other words it can be explained by motives common to all persons and organizations, not just those with supposed recondite vested interests.
“over the past few decades public health has been largely defunded”
Actually, since 1970, funding for the NIH and the CDC has met or outpaced economic growth every decade except this last one, where it has leveled off.
Although finding for public health means more than just funding for the CDC and NIH. I was thinking more of public health departments.
> I’m looking for an explanation for *why* the WHO and CDC resisted the aerosol approach
Yeah it seems like there are a few possibilities there and the distinction would matter.
Like was this:
1. WHO/CDCers generally did not believe the evidence
2. WHO/CDC insiders didn’t want to rock political boats
3. The WHO/CDC didn’t think the distinction mattered that much — people are already doing their best, etc.
4. Something else…
Maybe it’s just impossible to pull this stuff apart and nobody was recording anything, but at the end of the article there was the line:
> As Zeynep Tufekci noted in The New York Times, perhaps the biggest news of the pandemic passed with no news conference, no big declaration.
Which I don’t really get the biggest news of the pandemic point — it’s unclear to me what changes as a result of this (not that these changes can’t be important — I just don’t understand what they are). The messaging at the end seems to be buy lots of ventilation, so maybe the hope is that people who weren’t already buying ventilation will buy it now? Or maybe the change has legal implications for workplace safety?
My guess is people understand covid is airborne in closer to the literal sense of the word and not this medical sense (it seems understood in the comments here, at least). In the article there is:
> In an interview, the WHO’s Maria Van Kerkhove said that the change reflects the organization’s commitment to evolving its guidance … She maintains that the WHO has paid attention to airborne transmission from the beginning… But because that term has a specific meaning in the medical community, she admits to avoiding it… Does she think that decision has harmed the public health response, or cost lives? No, she says. “People know what they need to do to protect themselves.”
To speculate, in the critique-of-lockdown-effectiveness posts there’s the point that people can change their behaviors without a lockdown. This seems like the next leap (however unfounded this leap may be) — that people basically have all the information and do change their behaviors and so it just doesn’t really matter what the WHO prints on their website.
Anyway, it seems like there is still disagreement here. The NYTimes article says perhaps the biggest news, and WHO says the delayed change probably hasn’t harmed public health or cost lives.
The distal reason for the resistance is that aerosols sound too much like miasma, which had been debunked and replaced by germ theory. I don’t have the source at the moment but I believe you can find Wells discussing this in the 1930s.
The proximal reason is that masking and social distancing policies were based on falsely assuming the virus primarily spread via short-lived large respiratory droplets. These policies make little sense or can even be counterproductive in the case of aerosols.
+1. I too am very discouraged by this.
1. WHO/CDCers generally did not believe the evidence
2. WHO/CDC insiders didn’t want to rock political boats
3. The WHO/CDC didn’t think the distinction mattered that much — people are already doing their best, etc.
4. Something else…
The something else was the same something else all of us felt, unless we were exceptionally brave in facing the dark: it was wishful thinking.
It was hoping that things would be more manageable rather than less. It was fear. Bureaucracies and “suits” feel fear too — they just dress it up differently. Instead of saying outright “consider X” they go to great lengths to tell you all about the marginal evidence they have on-hand for “consider Y” where Y is less disagreeable than X. Further, the sophisticated among them will tell you how slipshod the miscellaneous evidence is for X in contradistinction to that for Y, which, although marginal, is “better put-together”. They keep fear at-bay by converting uncertainty into seeming precision; precision, like stardust, attaching to each piece of dead uncertainty, and the whole dead edifice of uncertainty amazingly levitates a few inches above the dead ground!
One of the biggest contributors to the “droplet spread” idea for me was the German study done back in January that contact traced the first German outbreak (backed by PCR diagnosis of all potential contacts) that resulted in something like 17 discovered infections among 212 subjects, and most of these were linked to close personal contact 15 minutes.
So, no matter what you qualify as aerosol or not, focusing on preventing these types of contacts, or mandating protection in especially these situations, seemed like a sensible way to focus public health policy.
If “droplets” are the big contributor, then a clear plastic face shield should basically 100% block transmission. But if it’s aerosols, then they’ll be carried with your breath around the face shield and generally fill up the air around your body through diffusion and air currents.
If “10-15 minutes” are required, then this seems even more evidence for *aerosols* as diffusion around to the breathing space of the others takes time. If it’s droplets, then you’ll be hit by them right away, as they travel several feet.
I do think it matters a lot, because if aerosols are the means of spreading then you can spread the virus even if you’re not in direct contact with others. For example, infected person goes into elevator on floor 1, gets off on floor 2, uninfected person gets in empty elevator on floor 3, goes down to floor 1… transmission. Or person walks into restroom recently after someone else flushes toilet. Or one person sits next to air conditioner, breathes viruses into airstream, fan blows them to other tables at restaurants (this is an actual case study), or people in a call center, all wearing masks, still transmit (also a case study).
Missing these kinds of transmissions because you’re not looking for them and they’re “impossible” by dogma, or even finding them but not understanding what they mean (the restaurant AC or call center) means you’re not protecting people properly, and people focus on the wrong things (ie. say handwashing and 6ft distance instead of HVAC).
The 10-15 minute thing does not seem to me to particularly favor either aerosols or droplets, because you need sufficient “viral load” to be infected. Aerosol view: you need exposure for 15 minutes to get enough viral load from enough aerosols at typical conversation distance. Droplet view: you need exposure for 15 minutes to get decent odds of a droplet hitting the target of your nose and mouth.
As for the time it takes for aerosols to diffuse around the breezing space of others, the diffusion time of aerosols over such distances is not markedly different from the diffusion time of molecules. My experience with farts suggests that this sort of diffusion is quite rapid.
Only one virus needs to infect a cell, then it replicates and creates many more copies of itself that are released and infect other cells where it replicates more.
If you plant more seeds at least one is more likely to sprout into a plant. And the second generation will produce more seeds than a single plant can. But one original seed is sufficient.
Anoneuoid –
> Only one virus needs to infect a cell
Just to check that you aren’t suggesting that “viral load,” or perhaps less ambiguously the amount of virus (whether droplet or aerosolized) a person is exposed to doesn’t translate into affecting the probability of developing (1) an infection and/or (1) a serious infection?
First off, I used the wrong term: it should be “infectious dose”.
As an infectious disease expert who knows better explained it to me, the body has various nonspecific response systems for dealing with an infectious agent, and they can generally handle a few hundred to a few thousand viral particles without much difficulty. But get much more than that and it’s too much to handle and the body needs to bring in disease-specific antibodies, which take time to develop if you don’t already have them.
From that, I gather that the probability of infection is very low for low doses of viruses, and stays very low until a certain fuzzy threshold is reached, after which it rapidly increases to near 1.
I could be wrong with that interpretation, but that’s how I understand it.
The thing is, this was the first outbreak in Germany, in a small auto parts manufacturer, and they didn’t miss any cases. Provably. The strain that later caused outbreaks in Germany came form Italy, that was genetically evident.
So, if these aerosol-only transmission types had played a major role in the epidemiology, that would’ve been detected.
There are some activities involving heavy breathing (such as singing) which make aerosol generation more prevalent, and the advice is different for those, but for normal contact, curbing droplet spread did enough epidemiologically to stop the first wave.
My point is, this advice wasn’t just based on 60-year-old assumptions, this was based on a very thorough observation of an actual outbreak cluster.
https://twitter.com/random_walker/status/1395374326241767428?fbclid=IwAR1_fhyA-fW9E9jXdz7V8Dy5SAECiI8hLWFuG5gCR31CEMuZ0n8S-kBEXBU
I thought this Twitter thread hits the nail on the head. This entire absurd episode is a massive black eye for public health and science. I can’t believe some here are actually excusing this.
How is it a black eye for science? A bunch of people agreeing on the same obviously wrong assumption for generations then saying everyone needs to listen to them is religion or scholasticism.
Interview: Donald Milton on Aerosol Transmission of Covid-19
An expert on aerosols discusses his early efforts to warn authorities about the airborne spread of Covid-19.
https://undark.org/2021/08/06/donald-milton-interview/
Joshua:
Sure, but I don’t trust Undark.
I remember that. But I can personally vouch for the interviewee
I wrote a lengthy description of this in a draft of a textbook of logical fallacies in scientific reasoning.
Langmuir wrote an article at the end of his career and he personally blamed his own “smugness” when he came to believe he may have been wrong about the nature of airborne infection, which deserves an award for cajones. There are only 43 citations to this article since 2000, so obviously, the fact that he signaled other researchers that they should revisit the question of what kinds of diseases can be airborne was ignored.
There is also a fallacious interpretation at the beginning of HIV research, partially caused by medical ethics as far as I can see. But when medical ethics prevents further study, it may be that our refusal to reason about causality unless it is proven (another logical fallacy) is to blame. From what I can tell, the medical community now collects observational data, which is evidence that they are learning. And what is sad is that social scientists are now of the belief that only experiments can lead to causal inferences. Ugh.
There is also the bizarre case of rheumatoid arthritis and Alzheimer’s. I have been telling this story for a decade, but I did not realize until writing my essay about this that there were NO TREATMENTS for Alzheimer’s until these researchers studying rheumatoid arthritis mentioned a bizarre fact: they found very, very low numbers of people with Alzheimer’s, as compared to the general population of similarly aged people. They wrote a letter to the editor reporting a strongly negative correlation (p< .005). This led to our understanding that Alz is a disease of inflammation and those on anti-inflammatories, which we did not know before.
This means that sometimes, correlation without causation can lead to significant scientific advances.
And there is also the story of Sarah Stewart who spent much of the 20th Century trying to show that viruses may be the source of some cancers. She was fired for it, but her dogged persistence finally got her a job at NIH. I am sure they apologized for their sexism (and racism as she was also Mexican American). (I am sure they did not, as she is rarely even cited). The WHO now believes that 10% of cancers are caused by viruses.
This is why the peer reviewers (and editors) need to stop using the question: "Do I agree with this?" as the gatekeeping question. And we need to stop refusing to publish research from observational research. And rather than having our methods training be focused on: teach them to use the correct method, we ought to teach students to navigate the problems associated with imperfect data for themselves, using a "teach a man to fish" logic.
Sources
https://www.smithsonianmag.com/science-nature/woman-who-revealed-missing-link-between-viruses-and-cancer-180972427/
Langmuir, Alexander D. "Changing concepts of airborne infection of acute contagious diseases: a reconsideration of classic epidemiologic theories." Annals of the New York Academy of Sciences 353, no. 1 (1980): 35-44.
Jenkinson, M. L., M. R. Bliss, A. T. Brain, and D. L. Scott. "Rheumatold arthritis and senile dementia of the alzhelmer's type." Rheumatology 28, no. 1 (1989): 86-87.
I should also say thank you to Professor Gelman for your work to help students with the logic of inference. I have a folder on my computer called “Awesome shit Gelman has said”
‘I have a folder on my computer called “Awesome shit Gelman has said” ‘
OK, that’s cool but I’ve said many of those same things – and without the benefit of being at a top tier uni or even having a stats degree!! Do you have a folder on your computer called “awesome things that Chipmunk said – even though he has no stats education and therefore has deeper organic and fundamental insight about stats than Gelman”?? Nooooooo……. Gelman gets all the chicks! Ooooo!!!!
My dad always hated the way I mowed the lawn but if he hired a “professional” who mowed it the exact same way he’d freakin gush over what a great job he did. (there are how many ways to mow a lawn?) Most people don’t understand anything. They just go by reputation.
ha ha ha!
It’s too bad the only two people in the world who would get that probably aren’t reading this blog, but it’s hilarious to me anyway! :)
Vanessa, I too have a folder on my desktop that just has cut/paste snippets of some things Dr. Gelman has written on this blog that I just really thought were awesome!
I have no such folder for Chipmunk’s posts. Chipmunk–are you doing ok? Are those seeds in your cheeks or 100-proof Old Forester?