How getting cholera wrong led to getting Covid wrong

So, one of the things I love about twitter is that a center-left Political Scientist obsessed with Covid and air quality can end up finding a center-left technology company guy who founded a bamboo shirt company (I’m wearing one now– most comfortable clothing I’ve ever owned) also obsessed with air quality, and strike up a meaningful correspondence.  In this case Jeremy Chrysler wrote a terrific article about how science getting the miasma theory of disease wrong essentially led to an over-correction that led science to largely get airborne transmission of disease wrong.  It’s really a fascinating history of science story with great details about cholera epidemics and, really, about how our overconfidence in how we’re just so much smarter now can lead to our downfall.  If you prefer the twitter thread version, here you go (it’s an excellent thread):

But, also, my favorite (long) part of the article:

Why was miasma theory so durable? Because science often resists change.

With a new, observable mechanism in place, and one that allowed for dramatic public health improvements through policy interventions, germ theory took hold. Even so, belief in miasma had endured for decades longer than it should have, despite all the evidence that is plain to us now and despite all the grinding, thankless work by dedicated scientists. 

As the history of science has shown though, the delay in adopting a new paradigm has been the norm in science, and the lessons of the past are a helpful warning to those inclined to resist change today. 

Thomas Kuhn, author of The Structure of Scientific Revolutions, writes that resistance to change is actually a part of the critical functioning of “normal science.” Normal science is a “cumulative enterprise” that relies on a basic agreement about what it is that scientists are working on. Without this commitment to a common foundation, scientists can’t collaborate across time and space. 

Most of the time, this resistance is helpful. 

Kuhn writes that

normal science often suppresses fundamental novelties because they are necessarily subversive of its basic commitments.”

Normal science is thus essentially conservative, especially when it comes to fundamental operating assumptions. It wouldn’t work otherwise. Conservatism is a feature, not a bug, as it helps preserve collective focus from distraction. 

When the operating assumptions are wrong, as they were with miasma, anomalies and inconsistencies thus initially get suppressed by the collective pressure of normal science. This is why the research of Snow, Semmelweiz, and Lister encountered resistance – all of their work went against the operating consensus. Their work started a revolution in science, but it did so in slow motion. 

Revolutionary science often meets fierce resistance, delaying progress. 

This is because revolutions in science are “tradition-shattering.” The Copernican Revolution, the theory of evolution, special relativity – they all encountered serious resistance en route to adoption because like germ theory, they rewrote fundamental assumptions.

When a revolution is finally achieved, the old theory is thrown out. 

But despite resistance, these revolutionary ideas are inexorable. Such was the case with germ theory. It took decades to complete, but once germ theory finally took hold it wouldn’t just be added to the idea that air carried disease, it would create a new foundation of understanding for all scientists who came after.

The foundational belief that the air carried disease was effectively abandoned and replaced by the understanding that germs did. 

In 1910, Charles Chapin helped finalize this replacement when he published The Sources and Modes of Infection, a seminal work in which he systematically argues that infections are spread by close contact, when one person spreads germs – bacteria, parasites, and the like – to another through direct contact. 

Unlike the superstitious miasma theory of old, contact transmission was supported by real evidence – organisms that could be observed and cultured from surfaces. Chapin even cites Snow’s work – he was effectively describing contact transmission before it had a name – among many documented examples of historical contact transmission that weren’t then recognized as such. And Chapin saw little reason to consider airborne transmission at all given what we now knew. 

Thus, belief in airborne transmission was discarded in favor of germ theory.

Chapin writes of airborne spread, “without denying the possibility of such infection, it may be fairly affirmed that there is no evidence that it is an appreciable factor in…our common contagious diseases. We are warranted, then, in discarding it...and devoting our chief attention to the prevention of contact infection. It will be a great relief to most persons to be freed from the specter of infected aira specter which has pursued the race from the time of Hippocrates…” 

Excerpt from Chapin

Note two things. First, Chapin is motivated in part out of a worry that people will avoid contact protections if they believe a disease spreads through the air. Many have speculated that this has been a part of our current reluctance too.

Second, the use of the the word “discard” here shows where we abandoned it. The airborne theory of disease transmission, which had been the dominant view for two thousand years, was being thrown out because the real cause of disease had been found. 

Chapin’s dismissive characterization of airborne transmission was tied to the then recent superstitious history of miasma and his fear of losing hard-earned progress of contact mitigation, but the attitude and tone he took toward aerosols has propagated through infectious disease literature ever since he published. Indeed, his words are echoed in this pandemic 110 years later. 

Chapin’s dismissal of airborne transmission still lives on. 

In July of 2020, JAMA published an article entitled Airborne Transmission of SARS-CoV-2, Theoretical Considerations and Available Evidence, in which the authors write “notwithstanding…the possibility of aerosol-based transmission, the data on infection rates and transmissions in populations…are difficult to reconcile with long-range aerosol-based transmission.”

It’s the same basic language that Chapin had employed

In many ways what is happening here is similar to what happened in the cholera pandemic in 1855. We have a theory which has been dominant for some time, and we see public health authorities resisting changes to that theory despite the fact that new science from outsiders offers a better explanation of how a pandemic disease is spreading. 

I love that a guy I just met on twitter with similar interests actually thought enough of me to have me read a draft and provide some feedback, but, mostly, I really love this finished product (for which I take no credit) and have been so happy to read.  


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