Air-Borne

Summary

99% Invisible: "Air-Borne" Episode Summary

Release Date: July 29, 2025

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Introduction to Airborne Microbiomes

Roman Mars opens the episode by contemplating the invisible life in the air we breathe. He juxtaposes his cautious approach to waterborne microbes with his obliviousness to airborne ones, setting the stage for a deep dive into the complex ecosystem of the aerobiome.

Quote:

"When I look at a body of water, I assume that it's teeming with microbes... But I don't apply the same scrutiny to the air I breathe." — Roman Mars [00:47]

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Carl Zimmer and the Aerobiome

Science writer Carl Zimmer, the author of Airborne, is introduced as the expert guiding listeners through the intricate relationship between air and disease. He explains the aerobiome as a vast, largely misunderstood ecosystem that plays a crucial role in both nature and human health.

Quote:

"The aerobiome is not just important for how nature itself works, but you are breathing in living things pretty much with every breath." — Carl Zimmer [01:18]

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Historical Perspectives: The Miasma Theory

Zimmer delves into the miasma theory, an ancient belief that diseases like the plague were caused by "corrupted air" or miasmas. This concept dominated for centuries, influencing urban planning and architectural designs aimed at promoting fresh air to prevent disease spread.

Key Points:

• Hippocrates and the four humors: Health was perceived as a balance of bodily fluids, disrupted by miasmas.
• Sanitarian Reforms: Urban improvements like canals and waste management were implemented to cleanse the air.
• Florence Nightingale's Hospitals: Designed with long corridors and ample ventilation to combat miasmas.

Quote:

"Miasma would actually affect the way people built their world, the way that cities were designed and the way that houses were built..." — Carl Zimmer [05:05]

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Max von Pettenkofer: The Last Advocate of Miasmas

A pivotal figure, Max von Pettenkofer, fiercely defended the miasma theory into the late 19th century. Despite emerging evidence supporting germ theory, Pettenkofer remained steadfast, even ingesting what he believed were cholera bacteria to prove his point—a dramatic act that ultimately led to his downfall.

Key Points:

• Cholera Epidemics: Pettenkofer attributed cholera to toxic fumes from the soil, emphasizing ventilation and clean air.
• Conflict with Germ Theory: Scientists like Robert Koch provided concrete evidence linking specific bacteria to diseases.
• Pettenkofer's Demise: His public ingestion of bacteria, based on flawed interpretations, ended in suicide after it was revealed he had consumed a harmless strain.

Quote:

"He was the last great defender of miasmas... by the late 1800s, Robert Koch was really starting to nail one disease after another." — Carl Zimmer [07:03]

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The Irony of Miasma Ideas in Modern Health

Despite the miasma theory being scientifically disproven, some of its principles—like the importance of ventilation and clean air—resurface as vital strategies in controlling airborne diseases such as tuberculosis and COVID-19.

Key Points:

• Ventilation and Filters: Effective building ventilation and air filtration systems can mitigate the spread of airborne pathogens.
• Ultraviolet Light: Once a tool for miasma control, UV light is now validated as a method to disinfect air.
• The Pettenkofer Number: Modern CO₂ meters, inspired by Pettenkofer's work, serve as proxies for measuring indoor air quality and ventilation efficiency.

Quote:

"The idea that the air can kill you with some of these infectious diseases. That's true. That's absolutely true." — Carl Zimmer [17:18]

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20th Century Shift and Persistent Reluctance

Zimmer traces the decline of airborne disease awareness through the 20th century, highlighting how early germ theorists like William and Mildred Wells struggled against entrenched scientific beliefs to advocate for recognizing diseases as airborne. Their work laid foundational concepts for understanding airborne transmission, yet acceptance remained limited until recent decades.

Key Points:

• William and Mildred Wells: Pioneered the understanding of airborne transmission through research on droplets and ventilation.
• SARS and COVID-19: These pandemics reignited discussions about airborne transmission, forcing a reevaluation of long-held public health practices.
• Institutional Resistance: Scientific and public health establishments were slow to adapt, often dismissing airborne transmission despite mounting evidence.

Quote:

"We were in a bad position when Covid hit in 2020 because so many of our buildings and our spaces were poorly ventilated." — Carl Zimmer [40:15]

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Modern Applications and Future Implications

The episode emphasizes the urgent need to integrate lessons from the past into contemporary building design and public health policies. By adopting strategies such as continuous air monitoring, improved ventilation systems, and the use of UV light, society can better safeguard against current and future airborne diseases.

Key Points:

• Air Quality Monitoring: Using CO₂ meters to assess and manage indoor air quality.
• Building Retrofits: Upgrading existing structures with better ventilation and filtration systems.
• Design Standards: Developing and enforcing indoor air quality standards akin to clean water regulations.

Quote:

"It's time to wake up and start to build safer buildings." — Carl Zimmer [41:29]

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Case Study: Club Cafe in Boston

Zimmer recounts his visit to Club Cafe in Boston, where retired tuberculosis expert Ed Nordell implemented far UVC lights to ensure the room was safe for gatherings. This practical application demonstrates how advanced air purification technologies can facilitate safe indoor interactions without compromising social experiences.

Quote:

"Ed was thinking, well, like, we need to get back together... and so he talked the club into letting him install these little far UVC lights on the ceiling." — Carl Zimmer [42:48]

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Conclusion: Embracing Healthy Air Practices

The episode wraps up with a call to action for architects, designers, and policymakers to prioritize indoor air quality. By learning from historical theories and modern science, societies can create environments that protect public health while allowing for communal and social activities.

Final Quote:

"We deserve to enjoy each other's company... We just need to take the right precautions." — Carl Zimmer [43:00]

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Production Credits

Produced by Emmett Fitzgerald, mixed by Martine Gonzalez, with music by Swan Real and George Langford. Special thanks to contributors and the 99% Invisible team for their dedication and creativity.

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Note: This summary excludes promotional content and advertisements present in the original transcript to focus solely on the episode's substantive discussions.

Transcript

[Carl Zimmer]

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[Roman Mars]

This is 99% invisible. I'm Roman Mars. When I look at a body of water, I assume that it's teeming with microbes. And for that reason, I wouldn't fill my water bottle from a puddle or a pond or probably even a stream, because I know that I have a chance of getting a waterborne disease. But I don't apply the same scrutiny to the air I breathe, which is a little odd because it, too is chock full of life.

[Carl Zimmer]

Scientists call it the aerobiome. It's this huge ecosystem that we really barely understand at all.

[Roman Mars]

This is science writer Carl Zimmer, who has written an amazing new book called Airborne, all about the life that is wafting about in the air all around us.

[Carl Zimmer]

The aerobiome is not just important for how nature itself works, but you are breathing in living things pretty much with every breath. You know, most of the time they don't kill you, but, you know, when you have a pandemic, sometimes a lot of people do die.

[Roman Mars]

Carl Zimmer's book is a scientific history of the air and its relationship to disease. I started reading the book for fun, but I decided to interview Carl on the show because it actually has a lot to do with architecture. Most of our breathing happens indoors, and yet modern architects rarely design buildings with airborne disease in mind. Carl Zimmer thinks that's in part because for over a century, scientific institutions have been reluctant to take the air seriously as an important vector for disease. We, we got a taste of this during the early days of the COVID 19 pandemic, when there was a lot of conflict and confusion about whether the virus was airborne and what airborne even means.

[Carl Zimmer]

But this conflict and confusion, it didn't start in 2020. I mean, the fact is that our struggle to understand the air and what the air means to us and our health actually goes back thousands of years.

[Roman Mars]

So, okay, so I want you to guide us through this history of how we think about the air and its relationship to disease. So where should we start?

[Carl Zimmer]

Well, if you go way back to the ancient world, there were a lot of concepts about the air being the cause of many diseases. And so Hippocrates would talk about miasmas, which were like a corruption of the air. You know, why is it that all these people in this village all got the plague around the same time? Well, it must be because there was a miasma in the air that just traveled along and everybody inhaled it and they all died. So there was this powerful concept which held on in one way or another for many, many centuries.

[Roman Mars]

Could, could you describe what, what was the conception of what a miasma was like? What was it made of? Like, I don't quite, quite get it.

[Carl Zimmer]

Of course you don't get it because you don't live in ancient Greece and you don't have an ancient Greek worldview. You know, I mean, you got to think about the world as being made of four elements. So you have to think about your body as being made of four humors. I mean, it takes a lot of rejiggering to. To really try to even begin to understand what Hippocrates is talking about. It's a corruption. Corruption was a very powerful idea in ancient Western thought in particular. And so, you know, you, you would have the four humors in your body which were in this delicate balance. And, you know, if you inhale this corrupted air, that would throw your humors out of balance. I should add, like, miasmas were believed to be caused by lots of different things. So they might be caused by bad weather, they might be caused by the stars, they might be caused by waste lying on the ground or stagnant water. So there are all these potential sources for corrupting the air. And then when you breathed it in, then you would get sick. And there were different miasmas for different diseases, you know, plague, influenza, on and on and on. Each one had its own miasma.

[Roman Mars]

So how did thinking about disease as a miasma affect the way people behaved?

[Carl Zimmer]

Miasma would actually affect the way people built their world, the way that cities were designed and the way that houses were built so canals would be built, you know, so that you didn't have water just getting stagnant. Waste would be required to be cleared out of the center of cities. When you had reform movements in Britain in, in the 1700s that were trying to improve the health of people in prisons, people were dying in prisons of, of diseases, including something they called jail fever. They thought what you needed to do was to bring in fresh air, because wholesome fresh air would replace the. The stagnant air that, you know, filled with miasmas that was building up inside these prisons. And so there was even a british prison that had a windmill built on the roof to try to circulate fresh air through the whole building. And so a lot of the response to this belief in miasmas was urban planning and architecture.

[Roman Mars]

I want to bring in this character or this person that is a character in your book named Max von pettenkofer. Could you tell me about him and where he sits in the miasma world?

[Carl Zimmer]

So max von pettenkofer was the last great defender of miasmas. He was born in 1818, and he died in 1901. And pretty much to the end, he was arguing and fighting passionately for miasmas as being the cause of diseases like cholera and typhoid and on and on and on. In his day, he was not considered a crank. In fact, just the opposite. He was revered. He was considered the world expert on cholera.

[Roman Mars]

And so what were van petenkofer's ideas about cholera?

[Carl Zimmer]

Cholera comes to Europe in the 19th century in this series of epidemics that are totally terrifying. A city would be running along smoothly, and everything seemed fine one day, and the next day, people are just dropping dead in the street. Their faces are turning blue. They are suffering violent cramps and diarrhea, and within a few days, they're dead. You know, thousands and thousands and thousands of people are dying in city after city after city. So what is it? So van pentenkofer believed that cholera was actually caused by fumes that came out of the ground, that there were the certain kinds of bacteria that could ferment, basically, in soil that was damp and just had just the right conditions. So you would have these fumes that they would release and they would build up inside of buildings, inside of people's homes, especially if they were poorly ventilated. So people would, you know, be breathing this stuff in and out, in and out, and it would create damage inside their bodies that would eventually trigger all the horrible, deadly symptoms of cholera. And so he was very concerned to keep the air safe.

[Roman Mars]

So what were his ideas about how to do that, about how to keep the air safe?

[Carl Zimmer]

Well, he believed that you have to prevent these fumes from reaching people. So one way you can do that is to try to avoid the circumstances in which these fumes can form. You can build buildings on soil that he believed was safer. For example, he made lots of changes in munich to the Water system so that you wouldn't have a lot of stagnant water sitting around, which he believed that would be a problem. He emphasizes ventilation. You want to get fresh air moving through your house or your office or your school, because if there's no way for air to get out, these fumes that he imagined were rising up from the ground are just going to get into these rooms and get trapped in there. And then you just breathe them and breathe them and breathe them. And he was part of a movement, you know, they called themselves sanitarians, and they wanted to help everyone. And so, you know, tenements in New York or hospitals for the poor in London or what have you, they were all trying to get fresh air to people. They were all trying to fight miasmas and thereby fight disease.

[Roman Mars]

I mean, you wrote that the New York City Board of Health forced the installation of 46,000 new windows throughout the city.

[Carl Zimmer]

City.

[Roman Mars]

Which sounds. That's something. That's an intense buy in. I mean, that's a very expensive proposition.

[Carl Zimmer]

Yeah, absolutely. Absolutely. I mean, you know, New York was much smaller of a city at the time, so that is just huge. Yeah, these sanitarians and these reformers were able to get a lot of things pushed through. And, you know, Florence Nightingale was very much part of this movement as well. And she designed new kinds of hospitals with long corridors and rooms branching off of them, all designed to maximize the flow of air, to get fresh air into for these patients, because she was convinced that they were getting sick not from contagious disease, but from miasmas.

[Roman Mars]

So as popular as the miasma theory was, the idea that bad vibes or animal carcasses or stagnant water was corrupting the air with poisonous fumes was obviously wrong. And over time, you get this competing philosophy, which is germ theory, which we now know is correct. Can you talk about how germ theorists started to win the battle of ideas against sanitarians like von Pettenkofer?

[Carl Zimmer]

You know, in the 1600s, people are starting to invent microscopes. And when they look through the microscopes, they suddenly discover there are all these tiny creatures that we didn't know about before. They would call them germs or microbes or, you know, bacteria. Like, they had all sorts of names for these things. And as early as the early 1700s, you had people saying, you know, these germs are the cause of diseases like plague and tuberculosis and on and on and on. And they got to be known as the. The contagionists. And everyone thought they were crazy. But Slowly, in the 19th century, the evidence started to accrue that, yeah, actually, there are particular microbes, species of microbes that can cause particular diseases. And by the late 1800s, there's a German scientist named Robert Koch who is really starting to nail one disease after another. And he establishes a link between one kind of bacteria and cholera. So this thing that Maxwell Pettenkofer was saying, oh, this is a cholera miasma. It's caused by these fumes. You gotta be careful about the air that you breathe, and blah, blah, blah. Robert Koch is saying, no, it's caused by this bacteria. You know, I find it in people's stool who are sick with cholera. You know, when there's an outbreak in a village and I go to a water tank in India, I find the same bacteria in there. Like, this is. This is it. And it is spread through water. The last great cholera outbreak was in. In the 19th century in Europe was in Hamburg in 1892. And Robert Koch, like, comes in there and says, okay, we have got to deal with this as it really is, as. As a waterborne microbe. And he brought in clean water, he disinfected houses, so on and so forth. The epidemic ended, and national laws were put in place to follow these rules to ensure clean water, to make sure our water doesn't make us sick. And von Penkofer refused to accept this. He just kept fighting with Coke over and over again. And now he's in his 70s, like, no, no, no, no, no.

[Roman Mars]

I mean, so much so that he, like, ingests a bunch of cholera just to prove his point. Like, he really put his money where his mouth is.

[Carl Zimmer]

Yeah, right. Right in his mouth, you could say. I mean, what happened was that von Pettenkofer sends a very mysterious note to a colleague of Robert Koch in Hamburg. Says something along the lines of, I would like to have a sample of this bacteria for my own study. So they send it to him. And he gets up one morning, and then he goes to a lecture hall, and he brings together all of his acolytes, and in front of them, he declares, hold, holding up this tube, that he is going to drink it. He's going to prove once and for all that cholera is not caused by bacteria. That it is, you know, that it is this. This airborne miasma disease. And, you know, his students are like, no, no, no, let us do it for you. And he's like, no, no. He says, I should die in the cause of science. Like a soldier on the field of honor. He was such a dramatic Person, you know, he, he, he actually like tried to be an actor when he was young. He, he ran off from pharmacy school for a year and was in the theater and then decided that wasn't going to work. But he never lost his dramatic streak. So he's putting on this performance and he kicks it back and over the next couple days he doesn't feel great, but he gets over it. And he sends a note to Robert Koch, you know, declaring that he was in good health, just wanted co. But what, what Pettenkofer didn't know is that when he asked for the, the bacteria that causes cholera coke and his pals kind of had an idea of what he wanted and they're like, what do we do? And amazingly, weirdly, you know, they said, let's give him some bacteria isolated from someone who had very mild symptoms, someone who did not die. So they took pity on him. They didn't, they didn't tell him what they had done, but they had just said like, oh, just give him, give him a harmless strain. Which he then drank and thought that he had proved at last that my asthmas were real. But by then, you know, the evidence was just piling up and piling up and piling up and you know, he got very depressed. And it's a very Sad story. In 1901, he, he, he shot himself. He committed suicide. And you know, the obituaries were polite at first, but eventually, as the germ theory of disease really took hold and miasmas really started to look like an embarrassing vestige of a superstitious age, Pettenkofer was lost to history. People would just say he is just one. Journal said he's just a shadow of a name. He was gone.

[Roman Mars]

So I'm struck by a certain irony when it comes to von Pettenkofer and the whole miasma theory, which is the underlying science, is complete nonsense. But some of his ideas about how to keep people healthy, particularly his focus on ventilation and clean air, actually do make sense in the context of airborne infections like tuberculosis or COVID 19. I mean, can you talk about that weird irony of being so wrong, but like, right enough that, you know, things are actually made better, you know, in the built world and for people's health.

[Carl Zimmer]

Yeah, it's strange that, you know, we think that when, you know, people are wrong, they're just wrong, wrong. And we think about the history of science as giving up wrong ideas to embrace the right ideas. Yeah. And you know, those people who were wrong, they're, you know, cast back into history as being the wrong ones.

[Roman Mars]

Right.

[Carl Zimmer]

You know, and, and their ideas, we would think of them as just nothing but superstition. And the idea that cholera or typhoid was something that was caused by you inhaling fumes, that's wrong. That's really wrong. And, and if you were to try to protect yourself from cholera, typhoid, that way, you would be so wrong, you'd be dead.

[Roman Mars]

Right.

[Carl Zimmer]

And yet, you know, the idea that the air can kill you with some of these infectious diseases. That's true. That's absolutely true. And in some ways we, we would do very well to go back to the ideas of people like Max von Pettenkofer and learn a lot from them, to learn about the importance of fresh air, of clean air, of ventilation, all these things that Pencoffer was developing in the 1860s. He was right in a lot of ways, as wrong as he was in other ways.

[Roman Mars]

Coming up after the break, Carl Zimmer and I talk about how in the 20th century our perception of the air totally flipped and we went from being too scared of the air to not scared enough. You booked your flights, you booked your place to stay. Now what? Adventure doesn't need to begin when you arrive with getyourguide Planning is as much of an experience as the trip itself. Get your Guide is an online platform where you can discover and book a range of activities cities in the US and around the world. Choose from over 150,000 experiences including guided tours, sightseeing, excursions, adventure activities, museum tickets and more. GetYourGuide brings the thrill of discovery to every moment leading up to your trip. No matter where you're headed, get yout Guide is the best way to connect with your destination with locally vetted and expertly curated experiences. There is something for everyone. Whether it's must see iconic attractions or or unexpected under the radar gems with flexible booking options, mobile tickets and millions of verified reviews. I'm one of those five star reviews. You'll find everything you need to simplify trip planning and book the best things to do in thousands of destinations. Discover and book experiences for your next [e-mail] that's getyourguide.com article makes it effortless to create a stylish, long lasting home at an unbeatable price. Whatever your personal style may be. Article offers a curated range of mid century, modern, coastal and scandi inspired pieces that not only shine on their own, but also pair seamlessly with nearly any other article product. Their carefully selected collections feature high quality meaningful pieces that will stand the test of time. There is no filler. Every item is chosen for its craftsmanship, design and lasting value. My house is like an article furniture longitudinal study. I sleep in an article bed my wife Joy works at and we eat at an article dining room table and we sit in article chairs. And it has been this way for years and years and years. All the furniture I've ever gotten from Article is still in service and performing at its peak. Article is offering our listeners 50 off your first purchase of 100 or more. To claim, visit article.com 99 and the discount will be automatically applied at checkout. That's article.com for $50 off your first purchase of $100 or more. The moment you realize your business needs to hire someone new, you pretty much have to hire that person like yesterday. So how do you find amazing candidates fast? It's easy. Just use Indeed. With Indeed Sponsored Jobs, your post jumps to the top of the page for your relevant candidates so you can stand out and reach the people you want faster. I ran my own business for most of my adult life and hiring is one of the hugest things that you have to take on when you run a business. Doing outreach and waiting for people to come back to you. All that stuff is so painful. I wish there was a podcast ad telling me about Indeed back then. There's no need to wait any longer. Speed up your hiring right now with Indeed and listeners of this show will get a $75 sponsored job credit. To get your jobs more visibility at Indeed.com Invisible just go to Indeed.com Invisible right now and support our show by saying you heard about Indeed on this podcast. Indeed.com Invisible terms and conditions apply. Hiring Indeed is all you need. This podcast is brought to you by Squarespace. Squarespace gives you everything you need to offer services and get paid all in one place, from consultations to events and experiences. Showcase your offerings with a customizable website delivery designed to attract clients and grow your business. With their collection of cutting edge design tools, anyone can build a bespoke online presence that perfectly fits their brand or business. And Squarespace's intuitive built in analytics tools can help you make smarter business decisions by letting you review website traffic, focus on key areas of engagement, and track revenue from bookings, invoices, or product sales all from one place. I set up Romanmars.com my Squarespace site so long ago. It was very simple and it's sort of dynamically refreshed by social media posts and other tools and so I don't really have to Fuss with it. Which is the greatest gift Squarespace can give me. Head to squarespace.com invisible for a free trial. And when you're ready to launch, use offer code Invisible to save 10% off your first purchase of a website or domain. Okay, so we're back with Carl Zimmer, and we just got done talking about the end of the miasma theory of disease in the late 1800s. So let's fast forward a little bit into the 1930s and 40s. By this point, there was broad acceptance that germs were causing diseases. And scientists thought you might spread germs by coughing saliva particles right into someone's face. But they didn't think that germs could float around in the air like smoke.

[Carl Zimmer]

That's right. So by the early 1900s, public health experts generally feel that, you know, they've got a handle on how diseases spread, and they're just of a few basic ways. Either they're spreading by contact. They're, you know, contaminated surfaces, sex, contaminated food, contaminated water. That's about it. And the air, which had been so dominant for. For many, many centuries now, you know, in the words of some of these public health experts, it was basically harmless. And, you know, someone even said, like, we should be relieved. That's great. We don't have to have to worry about these miasmas the way that, you know, generations and generations were worried about it. Relax. The air is fine.

[Roman Mars]

But in your book, you talk about these two scientists who started to really question whether that was actually true.

[Carl Zimmer]

Yeah. William and Mildred Wells. In the 1930s, this husband and wife team said, wait a minute. Like, that's not right. And, you know, they developed the basic ideas and the basic concepts for how actually airborne transmission really works. They understood that when we exhale, we're exhaling tiny droplets all the time. You don't have to be coughing or sneezing. And they might have viruses or bacteria in them, and if they're small enough, they'll just float along. And if you're in a poorly ventilated room, they're gonna be hanging around with you. And as people keep exhaling those droplets with the bacteria and the viruses in them, those concentrations are going to increase. And so your risk of getting a disease from these airborne germs will increase.

[Roman Mars]

And because miasmas were so out of fashion at this point, did they sort of fight. Have to fight the stigma of being, like, called masmasts or something like, like.

[Carl Zimmer]

Yeah, they did. They did. They actually wrote, we're not talking about miasmas. We're not miasmatists. Please, like, listen to us. Listen to what we have to say, and don't dismiss us as if we were from 400 years ago. We're talking about real physics right now and based on real experiments. And this could be a major source of disease. They were concerned, for example, that the influenza pandemic of 1918, which had killed 50 million people, they were saying, you know, that might have been airborne and, you know, tuberculosis, one of the biggest killers, year in, year out, they're saying, we think this is airborne, too. And we're not talking about mysterious Myanmars. We are germ theorists. There are germs that are doing this, but they're going through the air. They're traveling through the air, and you can stop them in the air.

[Roman Mars]

But despite Mildred and William Wells research showing that certain diseases were traveling through the air, that the scientific establishment remains pretty reluctant to jump on the idea of airborne infection. And this remains true, really, up until the 21st century.

[Carl Zimmer]

Yeah. William Wells dies in 1963. And, you know, there's a tiny little obituary for him, but his work is pretty much forgotten right after that, except for a few people that are trying to sort of carry on his memory and his ideas. But for the most part, it's forgotten. And in 2003, in China and in Hong Kong, suddenly there's this pneumonia that breaks out, SARS that, you know, can cause quite a lot of people to die, and it's spreading in strange ways. You know, there was an outbreak in a hospital where there were cases that went, you know, new cases that cropped up all the way down a ward from a patient, like a long distance. And people were like, how's this happening? And there was apartment block where lots of people were getting sick, so much so that this giant apartment block had to be emptied out. People were sent off outside of Hong Kong so that the building could be disinfected. And so as a few scientists started to look carefully at that and think about that, and how do you get that sort of spread? They're like this. These conventional ways we talk about don't. They don't make sense. And they started to dig into this old, old literature about airborne disease. William and Mildred Wells, who they had not heard of, like, they had to rediscover these folks and say, like, huh, this seems like this explains it. It seems like SARS is airborne. And so you had this small group of people in the early 2000s who were studying SARS, who were studying influenza, who are actually trying to Capture the droplets coming out of people's mouths and actually finding those viruses that were in the droplets. And they were doing this very basic research, but pretty much ignored by public health community. They just kept saying, no, no, no, this. This doesn't matter. This can't happen. It's not airborne. They just wouldn't accept it. Right up through into the COVID pandemic.

[Roman Mars]

Yeah. And I'm still just like, why? Why do you think scientific institutions have been so reluctant to see airborne infection for what it is? I mean, because, I mean, when you say this is happening in 2003 and then developing, you know, up until today, it's just like, usually you read science history books and you go, oh, those dummies didn't know anything back then, or whatever. And you, like, it's so obvious now. And that this is a fight that's brought right to our contemporary doorstep is so shocking to me.

[Carl Zimmer]

Yes, certainly, like, working on this book was just really vexing in a sense that, like, I'd be reading things from the 1930s where I'm like, oh, right, yeah, like, okay, like all the stuff that we're. We've learned in the past few years about airborne disease, like, we didn't learn this. We weren't the first. You know, like, people were understanding this stuff in the 30s, and it wasn't a secret in the 30s either. You know, there were newspaper articles about William and Mildred Wells. Not only had they established that diseases might be able to spread through the air, but they could kill them in the air. They discovered that ultraviolet light could disinfect the air. And so you had articles saying, oh, like, we are going to be protected in the future. Schools and theaters and hospitals and, you know, public spaces will be protected by ultraviolet light. So we don't have to worry about things like the 1918 flu pandemic in the future. This is what people were thinking in the 1930s, and then it was. Went away. You know, these are powerful, durable ideas that take hold and don't move very easily.

[Roman Mars]

Right. And we saw this persistent reluctance to embrace the reality of airborne infection as recently as five years ago, during the early days of the COVID pandemic. I don't know, part of me felt like the reason the public health officials didn't want to declare that Covid was airborne was just because they knew that our society was so ill prepared to deal with a disease like that.

[Carl Zimmer]

There are things you can do, but it takes a lot of work. And so if you treat a disease as if it is only spread through contact or through very large droplets that only go a very short distance, you know, three feet or something like that. There are things that you can do both in hospitals and in the community that are pretty straightforward. You know, you just. You just tell people, like, okay, you know, if you're not feeling well, you know, stay at home. If you see someone who's sick, keep an arm's length for them and you'll be fine. You know, Whereas if you are dealing with an airborne disease that is raging through your community, you gotta, like, deal with that really seriously on. On another level. Because the. Because now the air itself effectively is making people sick. And so you have to deal with the air as a whole. And that's not something that people are eager to embrace.

[Roman Mars]

Yeah, we're all like the mayor of Amity, you know, island, and we're just not willing to accept that Jaws is here, you know what I mean? Because it just. It's too much to handle, you know?

[Carl Zimmer]

That's right. And I mean, I'm not just inferring this. You know, the fact is that during the COVID pandemic, when there were scientists who were saying this thing looks airborne and you, the World Health Organization, need to treat it that way, The World Health Organization responded to them saying, we are not going to tell countries with limited health care budgets that they're going to have to go spend it all to deal with big airborne control systems when, you know, we're not. We're not entirely convinced of it. People actually said this out loud.

[Roman Mars]

Yeah, yeah, yeah, those beaches will be open on July 4, is what they said, basically. So it took way too long. But eventually we recognized COVID 19 as an airborne infection. And that recognition led to some changes in our behavior, you know, like outdoor dining and masks. But you personally had a change in your lifestyle that I think is pretty neat. Can you talk about the little device that you now carry around with you to help you measure the level of ventilation in indoor spaces?

[Carl Zimmer]

I have a carbon dioxide meter that I keep with me, and I'm looking at it now. So when we started talking, I had the window open just because it's a nice day here. And it was that 441 parts per million. And then I thought I'd close the window so that, you know, if someone starts mowing their lawn outside, it wouldn't bother our conversation. And it's gone up to 746 parts per million since we've been talking. That's just my own carbon dioxide.

[Roman Mars]

I mean, this strikes me as super funny to me, because the inventor of measuring CO2 and who sort of pioneered that, and in fact, the sort of count of CO2, the Pettenkofer number, is Max von Pettenkofer, the miasmatist. You know, the last standing miasmatist.

[Carl Zimmer]

It's. It is. It is crazy. It is crazy. This guy who. Who was. Yeah. Was willing to drink cholera bacteria to prove that his miasma theory. That's what we call it. We call it. Now that we call it. We still call it the Pettenkoffer number.

[Roman Mars]

And really, because it serves as this useful analog for something else. It's not like you're measuring the amount of bacteria or viruses in the. You're just measuring the CO2 load, which means it's gone through your body and expelled again.

[Carl Zimmer]

Yeah. So Pettenkoffer, Maxwell Pettenkofer, thought that he couldn't directly measure the miasmas, so he would use carbon dioxide as a proxy for the ventilation in a room. You know, he could say a room that has high CO2 is poorly ventilated and therefore can be dangerous if there are fumes that rise into it. We can use our carbon dioxide meters to also measure the ventilation in rooms. And if it's a poorly ventilated room and there are a lot of people, the carbon dioxide level is going to build up, and along with that, so are the little droplets that we exhale. And if somebody in the room has got Covid or has got tuberculosis or has got the flu, has got measles, I got a whole set of airborne diseases. The risk that you will get sick goes up.

[Roman Mars]

So when your CO2 meter gets to the Pettenkofer number, above that number where you're uncomfortable, what do you do?

[Carl Zimmer]

If I'm on a plane and, you know, I'm not able to get off of it, I will break out my mask, you know, and then 95 respirator. Because I know from lots of research that scientists have done that N95 respirators are really good at preventing you from inhaling airborne viruses or bacteria or what have you.

[Roman Mars]

That seems like a very responsible course of action to put on a mask, if you notice the number coming up. But should we demand a world in which the expectation is that this number shouldn't get up that high, you know, to begin with, or that the. The built environment should be taking care of us in some way?

[Carl Zimmer]

Oh, absolutely. If you are looking at a carbon dioxide meter and it's going up over, you know, a thousand parts per million, I mean, that's Telling you that we're dealing with a systemic failure. We're dealing with a failure to protect the air for all of us. This, this air in our indoor spaces, we share it. So, you know, we want to find ways to actually make that air healthier for everybody. And there are lots of ways that you can do that.

[Roman Mars]

So one of the interesting ideas in your book is once we have determined that the air, the indoor air in particular, is full of this aerobiome that could make us sick, is that we should think of it like we think of tap water getting clean water. Like if tap water was spreading a disease, we would fix that problem right away. Should we be thinking about air in this way?

[Carl Zimmer]

Absolutely. Absolutely, yes. And many of the scientists who led the charge to get the world to recognize that Covid is airborne have been continuing to fight for clean air. They have proposed a whole set of benchmarks that buildings should meet in order to ensure that we're not at really great risk of getting sick so that we don't have these super spreader events.

[Roman Mars]

And so how do we do that? Like, how do we move towards a world where healthy air is an expectation the way clean water is an expectation?

[Carl Zimmer]

Well, I mean, I think to begin with, people need to monitor the air. And then if you've got a space that was built poorly and is poorly ventilated, you got to find out ways to make them better ventilated. Back in, you know, the 1800s, New York City said, okay, we're, we're chopping windows into buildings, right? We don't necessarily have to do that. But, you know, there are ways to retrofit buildings so that you can bring in more fresh air to mix into the ventilation systems. That's one way you can use filters, you know, like HEPA filters and other types of filters. Those work. In some circumstances, ultraviolet light might actually work really well. There still needs to be more testing to really nail down the best way to use it. But we've known since the 1930s that ultraviolet light can disinfect air, so that that could be another tool. And then when new buildings are built, you know, they need to take these, these facts into consideration. It's a lot easier to build a healthy building than it is to try to retrofit a sick building. You know, building engineers and building engineer societies are thinking about these issues very seriously. And some of them are implementing these things into their, into their buildings designs, which is great. But, you know, it's just on a sort of case by case basis. You know, you don't Walk into some building and go into a bathroom and, you know, washing your hands, thinking, well, I hope this building, you know, has clean water that won't give me cholera. You know, you don't say that because you don't have to say it because there are standards for that. So there's no country in the world yet that has standards along the lines of what I'm talking about.

[Roman Mars]

I mean, could there be standards for indoor air quality that could be met?

[Carl Zimmer]

Oh, yeah, yeah. No, I mean, these scientists who championed recognizing Covid is airborne. They have come out with proposed standards to meet. There have been model bills that have been drafted at Johns Hopkins University. It's all in place that it can all go, but there is still a lot of inertia.

[Roman Mars]

I mean, this seems like a real call to arms and a provocation for architects and designers in particular, like, you know, like to make this central to the way that they're designing our built world is to prepare us for this.

[Carl Zimmer]

Yeah, absolutely. I mean, we, we were in a bad position when Covid hit in 2020 because so many of our buildings and our spaces were poorly ventilated and were just great places for, for this virus to build up and go from one person to another, spreading around like smoke. I mean, that was, you know, that's the, one of the particular cruelties of diseases like Covid because they prey on us when we come together. I do think we, we deserve to enjoy each other's company and not just, you know, out, out in the park. The, you know, outside is fine, but inside is important too. And, and, and there are ways that we can make that experience safer and that will help us for diseases that we deal with serving on a day to day basis now, like familiar diseases. And we do have to think about the next pandemic because unfortunately there will be one. And you know, if it's airborne the way Covid was, that will really turbocharge it and make it, you know, particularly bad. It is definitely a wake up call. And I mean, you know, this wake up call started in, most recently in 2020. So we've had five years of wake up calls.

[Roman Mars]

So it's time to stop hitting the snooze button.

[Carl Zimmer]

It's time to wake up and start to build safer buildings.

[Roman Mars]

So one of the final scenes of this book is at Club Cafe in Boston and it is kind of doing some of the things that you are recommending in terms of how to make our air biome safe for us. Can you describe what it's like there and what they're doing so.

[Carl Zimmer]

In working on the book, I got to know a retired tuberculosis expert named Ed Nordell, and he had worked a lot in using ultraviolet light to protect homeless shelters when there were tuberculosis outbreaks happening. So Ed, in his retirement, discovers he really likes to sing. He likes to sing cabaret songs. And there's this club called Club Cafe, where every week, in a little space called the Napoleon Room, people get together, and there's a piano in there, and they take turns singing songs. So after people got vaccinated, you know, Ed was thinking, well, like, we need to get back together. We need to get together. And so he talked the club into letting him install these little far UVC lights on the ceiling in the Napoleon Room.

[Roman Mars]

And far UVC lights are this new kind of ultraviolet light fixture that you talk about in the book that they can still disinfect the air, but they're designed in such a way that they won't burn your skin or hurt you.

[Carl Zimmer]

That's right. And that would be, you know, the ultimate safe space. You could go in there, you could sing, and you could be pretty confident that you wouldn't get sick from COVID And he invited me along to join him one night. So me and my wife came, and we had a great time singing away and just enjoying this. This experience with. With other folks quite confident that we were not going to get Covid while we were there, and we didn't. And, you know, Ed is not aware of anybody who has gotten Covid coming to the Napoleon Room for these performances. So, you know, I think that gives you a picture of what life could be like, taking airborne disease seriously. It doesn't mean that we have to be all in lockdown, in total isolation, and being really depressed. We can get together, we can do stuff, we can sing, we can have a good time. We just need to take the right precautions.

[Roman Mars]

Yeah. Carl Zimmer, thank you so much for talking with me. I enjoyed the book so much. There's so many details in the book that we didn't cover, but I just. So I encourage people to read it, and it's. It's so much fun. Thank you so much for talking with me.

[Carl Zimmer]

Oh, thank you so much for having me.

[Roman Mars]

99% invisible was produced this week by Emmett Fitzgerald, mixed by Martine Gonzalez, music by Swan Real and George Langford. And, hey, just a heads up, Emmett is going to be interviewing author and 99pi contributor Sam Block at the Commonwealth Club in San Francisco on Tuesday, July 29th. They'll be talking all about Sam's fantastic new book, which is called Shade the Promise of a Forgotten Natural Resource. If you're in the Bay Area, you should totally check it out. Kathy Tuohy is our executive producer. Kurt Kohlstedt is the digital director. Delaney hall is our senior editor. The rest of the team includes Chris Barube, Jason De Leon, Christopher Johnson, Vivian Leshma, Dawn, Joe Rosenberg, Kelly Prime, Jacob Medina Gleason, and me, roman Mars. The 99% invisible logo was created by Stefan Lawrence. We are part of the SiriusXM podcast family now headquartered six blocks north in the Pandora building in beautiful uptown Oakland, California. You can find us on all the usual social media sites as well as our own Discord server. There's a link to that as well as every past episode of [e-mail].

[Carl Zimmer]

There's a time and a place for a.

[Roman Mars]

Filet of fish, but breakfast is for sausage biscuits.

[Carl Zimmer]

McDonald's breakfast comes first.

[Roman Mars]

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