Air-Borne

0:00This 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. Scientists call it the aerobiome. It's this huge ecosystem that we really barely understand at all. 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.

0:49The 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. 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.

1:36We 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. 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.

2:06So, 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? 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.

2:51Could you describe what was the conception of what a miasma was? Like, what was it made of? Like, I don't quite get it. 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 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 would have the four humors in your body, which were in this delicate balance.

3:35And, you know, if you inhale this corrupted air, that would throw your humors out of balance. Actually, yeah, 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 were 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, so on and on and on. Each one had its own miasma. So how did thinking about disease as a miasma affect the way people behaved?

4:24Miasma 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 the 1700s that were trying to improve the health of people in prisons, people were dying in prisons of diseases, including something they would call jail fever. They thought what you needed to do was to bring in fresh air, because wholesome fresh air would replace the stagnant air filled with miasmas that was building up inside these prisons.

5:15And 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. I want to bring in this character, this person that is a character in your book named Max von Pettenkoffer. Can you tell me about him and where he sits in the miasma world? 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.

6:06In his day, he was not considered a crank. In fact, just the opposite. He was revered. He was considered the world expert on cholera. And so what were Van Pettenkofer's ideas about cholera? 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. And thousands and thousands and thousands of people are dying in city after city after city.

6:51So what is it? So Van Pettenkofer 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 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.

7:35And so he was very concerned to keep the air safe. So what were his ideas about how to do that, about how to keep the air safe? 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.

8:23Because 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. I mean, you wrote that the New York City Board of Health forced the installation of 46 ,000 new windows throughout the city, which sounds, I mean, that's an intense buy-in.

9:07I mean, that's a very expensive proposition. Yeah, absolutely. Absolutely. I mean, you know, New York was much smaller of a city at the time. So that is just huge. Yeah. But these sanitarians and these reformers were able to get a lot of things pushed through. And 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 for these patients. Because she was convinced that they were getting sick, not from contagious disease, but from miasmas.

9:47So 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 Pettenkoffer? 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 bacteria.

10:32Like 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 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.

11:25So this thing that Maxwell and Pettenkoffer was saying, oh, this is a cholera miasma. It's caused by these fumes. You got to 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 it. And it is spread through water. The last great cholera outbreak was in the 19th century in Europe, was in Hamburg in 1892. And Robert Koch comes in there and says, okay, we have got to deal with this as it really is, as a waterborne microbe.

12:09And 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, you know, to make sure our water doesn't make us sick. Yeah. And von Pettenkofer refused to accept this. He just kept fighting with coke over and over again. And now he's like in his 70s, like, no, no, no, no, no. 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. Yeah, 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.

12:57Says 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, 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 airborne miasma disease. And, you know, 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.

13:41He was such a dramatic person. You know, he actually like tried to be an actor when he was young. 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 a dramatic streak. So he's putting on this performance and he kicks it back. And And over the next couple of 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 Koch to know. But what Pettenkoffer didn't know is that when he asked for the bacteria that causes cholera, Koch and his pals kind of had an idea of what he wanted.

14:26And they're like, hmm, 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 tell him what they had done, but they had just said like, oh, just give him a harmless strain, which he then drank and thought that he had proved at last that my asthma 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 shot himself. He committed suicide.

15:03And, 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 a, one journal said he's just a shadow of a name. He was gone. So I'm struck by a certain irony when it comes to von Pettenkofer and the whole miasma theory, which is, you know, 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.

15:50I 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? 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. And, you know, those people who were wrong, they're, you know, cast back into history as being the wrong ones. 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.

16:47That's really wrong. And if you were to try to protect yourself from cholera or typhoid that way, you would be so wrong you'd be dead. Right. 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 would do very well to go back to the ideas of people like Max von Pettenkhofer and learn a lot from them. to learn about the importance of fresh air, of clean air, of ventilation, all these things that Penkoffer was developing in the 1860s. He was right in a lot of ways, as wrong as he was in other ways.

17:39Coming 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.

18:05Okay, 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. 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 there are just a few basic ways.

18:47Either 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 many, many centuries now, you know, in the words of some of these public health experts, it was basically harmless. And, you know, somebody even said like, we should be relieved. That's great. We don't have to have to worry about these miasms the way that, you know, generations and generations were worried about it. Relax. The air is fine. But in your book, you talk about these two scientists who started to really question whether that was actually true.

19:24Yeah. 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 going to 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.

20:12And so your risk of getting a disease from these airborne germs will increase. And because miasmas were so out of fashion at this point, did they sort of fight the stigma of being called miasmatists or something like that? They did. They did. They actually wrote, we're not talking about miasmas. We're not miasmatists. Please, 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've been airborne.

21:01And, 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 myansis. 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. But despite Mildred and William Wells' research showing that certain diseases were traveling through the air, the scientific establishment remains pretty reluctant to jump on the idea of airborne infection. And this remains true really up until the 21st century. Yeah.

21:37William 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 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 can cause quite a lot of people to die. and it's spreading in strange ways. There was an outbreak in a hospital where there were cases that went, new cases that cropped up all the way down a ward from a patient, like a long distance. And people were like, how is this happening?

22:25And there was an 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, these conventional ways we talk about, 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. They had to rediscover these folks and say like, huh, this seems like this explains it.

23:06It 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 were 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. Yeah. And I still just like, why? Why do you think scientific institutions have been so reluctant to see airborne infection for what it is?

23:51I 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're 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. Yes. Certainly working on this book was just really vexing in the sense that I'd be reading things from the 1930s where I'm like, oh, right. Yeah. Okay. All this stuff that we've learned in the past few years about airborne disease, like we didn't learn this.

24:37We 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, we are going to be protected in the future. Schools and theaters and hospitals and 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.

25:14This is what people were thinking in the 1930s, and then it went away. These are powerful, durable ideas that take hold and don't move very easily. 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. 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.

26:15You know, 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 got to like deal with that really seriously on another level. 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. Yeah. We're all like the mayor of Amity Island, and we're just not willing to accept that Jaws is here, you know what I mean?

26:59Because it's too much to handle, you know? That's right. And I mean, I'm not just inferring this, 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 healthcare 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 entirely convinced of it. People actually said this out loud. Yeah, yeah, yeah. Those beaches will be open on July 4th, is what they said.

27:47Basically. 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? 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 at 441 parts per million.

28:29And then I thought I'd close the window so that 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. 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 Pettenkoffer number, is Max von Pettenkoffer, the miasmatist, you know, the last standing miasmatist. It is crazy. It is crazy. This guy who was willing to drink cholera bacteria to prove his miasma theory. That's what we call it now.

29:16We still call it the Pettenkoffer number. 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. You're just measuring the CO2 load, which means it's gone through your body and expelled again. Yeah. So Pettenkofer, Max von 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. 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.