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A few years ago, when I still had confidence in our modern ability to fight viruses, I pored over a photo essay of the 1918 flu pandemic. How quaint, I remember thinking, as I looked at people bundled up for outdoor classes and court and church. How primitive their technology, those nurses in gauze masks. How little did I know.

I felt secure, foolishly, in our 100 additional years of innovation. But it would soon become clear that our full-body hazmat suits and negative-pressure rooms and HEPA filters mattered little to Americans who couldn’t find N95 masks. In our quest for perfect solutions, we’d forgotten an extremely obvious and simple one: fresh air. A colleague joked, at one point, that things would have gone better in the pandemic if we still believed in miasma theory.

Miasma theory—discredited, of course, by the rise of germ theory—held that disease came from “bad air” emanating from decomposing matter and filth. This idea peaked in the 19th century, when doctors, architects, and one particularly influential nurse, Florence Nightingale, became fixated on ventilation’s importance for health. It manifested in the physical layout of buildings: windows, many of them, but also towers erected for the sole purpose of ventilation and elaborate ductwork to move contaminated air outdoors. Historic buildings still bear the vestigial mark of these public-health strategies, long after the scientific thinking has moved on.

The obsession with ventilation—and miasma theory in general—was indeed wrong when it came to pathogens such as cholera and yellow fever that we now know spread through other means (water and mosquitoes, respectively). But it did make sense for the diseases that invisibly stalked people through 19th-century air: measles, tuberculosis, smallpox, influenza—all much diminished as threats in the 21st century. “We’ve gotten so good at preventing so many diseases, there’s been a loss of knowledge and a loss of experience,” Jeanne Kisacky, the author of Rise of the Modern Hospital, says. Science is not a simple linear march toward progress; it also forgets.

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Today, amid a pandemic caused by a novel airborne virus, these old ideas about ventilation are returning. But getting enough schools and businesses on board has been difficult. Fixing the air inside modern buildings, where many windows don’t or barely open, means fighting against the very nature of hermetically sealed modern buildings. They were not built to deal with airborne threats. Nineteenth-century hospitals were.


That era saw the rise of well-ventilated “Nightingale pavilions,” named after Florence Nightingale, who popularized the design in her 1859 book, Notes on Hospitals. As a nurse in the Crimean War, she saw 10 times more soldiers die of disease than of battle wounds. Nightingale began a massive hygiene campaign in the overcrowded hospitals, and she collected statistics, which she presented in pioneering infographics. Chief among her concerns was air. Notes even laid out exact proportions for 20-patient pavilions that could allow 1,600 cubic feet of air per bed.

Florence Nightingale / Wikimedia Commons

Each pavilion was a separate wing, radiating from a central corridor. And it had large windows that faced each other, which allowed a cross breeze to blow between the beds. The windows stayed open no matter the weather. There were stories, Kisacky told me, of hospitals in winter where “the patients are closing the windows, and the nurses are opening them. And the doctors come and knock the glass out to make sure they stay open.” In some pavilions, a central fireplace heated the room, so that contaminated air rose out of the ward via the chimney effect. That heat might have been nice in the winter but “they would run fires in the fireplaces in August to keep the air moving,” Kisacky said. “You wouldn’t want to be the patient in the bed closest to that.”

The pavilion-plan hospitals formalized the fear of “bad air” in hospital design, but the idea is much older. The Greek physician Hippocrates warned in the fifth century B.C. that bad air was the cause of pestilence. People in the Middle Ages believed some version of this too. The word miasma, which dates to the 17th century, comes from the ancient Greek for “pollution.” In the 19th century, the fear of outbreaks fueled new sanitation campaigns to rid cities of miasma.

Homes needed ventilation as well. In Victorian England, reformers successfully fought a window tax that penalized large windows, says Henrik Schoenefeldt, an architectural historian at the University of Kent. Bigger windows meant better ventilation. One doctor, Schoenefeldt told me, even railed against small windows as a “crime” that was killing people. When I was Zooming with another historian of architecture, Harriet Richardson Blakeman of the University of Edinburgh, she pointed her webcam up toward the ceiling. Above the door was a grate, which ventilated the room that had become her office in her Victorian-era home. (Blakeman thinks the grate may have actually been added some decades after the house was first built, as ventilation continued to be a concern.)

The massive growth of cities in the 19th century also sparked the creation of bigger and more elaborate public buildings, which meant the creation of bigger and more elaborate ventilation systems in new museums, prisons, and courthouses. “There are new types of buildings being invented to respond to urbanization,” Alistair Fair, an architectural historian also at the University Edinburgh, says. This was a time of innovation in ventilation too. In these complicated buildings, simple windows and chimneys would no longer do. Instead, intake vents were installed, as were ducts that wove through the walls and floors.

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A famous example is the Palace of Westminster, in London, whose construction began in 1840. The building’s architect consulted with a doctor, David Boswell Reid, and Reid suggested extensive revisions to the architectural plan to improve ventilation. The two iconic towers of Westminster—the Victoria Tower and the one that holds Big Ben—are both also ventilation towers that helped draw warm, stale air out of the buildings. Reid further insisted on an expensive third tower, the Central Tower, for the sole purpose of ventilation. The ventilation system as a whole, which also included mechanical fans, valves, and a series of air chambers in the basement, accounted for a quarter of the building’s costs. Physically, too, “that system, when it was completed, took up about a quarter of the entire building,” said Schoenefeldt, who has extensively studied historical ventilation in Westminster.

The system’s physical remnants are still in the building, now unused. Even in the 19th century, the building’s ventilation did not always work as designed—Reid was a doctor, not an engineer, after all—but the principles of his designs were influential. “The Palace of Westminster was, at the time, the technologically most sophisticated building constructed in Europe,” Schoenefeldt told me. Its ventilation system inspired those in the era’s new museums, concert halls, and courthouses.  

By the late 19th century, scientists were developing the beginnings of germ theory. John Snow had drawn his famous map of a cholera outbreak, which he traced to a single water pump. Louis Pasteur had shown that organisms cannot spontaneously generate in sterilized broth. And Robert Koch had identified the microorganisms that cause tuberculosis, cholera, and anthrax. But germ theory did not immediately do away with the importance of fresh air. “Early understandings of the germ, which emphasized its ubiquitous presence in air and water and its hardiness outside the body, neatly harmonized with already accepted modes of protection,” Nancy Tomes, a science historian at Stony Brook University, writes in The Gospel of Germs. The shift, like most paradigm shifts in science, was gradual.

For hospitals, the pavilion style continued into the 1930s, Annmarie Adams, an architectural historian at McGill University, told me. The 1918 flu pandemic struck at a time when germ theory was taking hold but people still recognized the importance of air. Even in modern hospitals today, where hand-washing and disinfection are paramount, the flow of air remains tightly controlled. Infectious patients are put in negative-pressure rooms, which contaminated air cannot escape. Immunocompromised patients are put in positive-pressure rooms, where contaminated air cannot enter. If anything, the flow of air is controlled in ever more sophisticated ways.

Outside hospitals, though, the menace of “bad air” has faded away. Airborne diseases simply don’t exist the way they did 100 years ago, Tomes says. Measles and smallpox have been vanquished through vaccines. Tuberculosis is treatable with antibiotics. The common remaining airborne pathogens are the cold and flu, diseases taken so unseriously that you might be docked for missing school or work on account of them. Without deadly airborne pathogens in the literal air we breathe, we’ve lost an intuitive sense of their invisible danger. And we’ve lost the relatively simple ways of mitigating that danger. Fresh air became less important; homes and workplaces were sealed up for energy efficiency.

Imagine, Tomes said to me, a sci-fi movie featuring a scary new virus. You would probably picture people protecting themselves with space suits and respirators. “Nobody ever goes to open a window,” she said. Who would have thought that the key to fighting this novel coronavirus would be as simple as fresh air? Only everyone 100 years ago.


Before COVID-19 hit last year, Linsey Marr, an environmental engineer at Virginia Tech, was one of the few scientists already studying airborne transmission of viruses. She told me she would read medical textbooks that claimed pathogen-laden droplets from our mouths fell to the ground within six feet. Until recently, however, scientists couldn’t measure what remained airborne, because they had no way of collecting delicate live viruses from the air.

There were other signs the textbooks were off, though: Marr knew, based on simple calculations she did with her undergrad students, that droplets of a certain size could linger midair. And papers going back decades suggested that common respiratory ailments such as the flu were indeed airborne, which official medical sources kept downplaying. “I just kind of figured, well, maybe 30 years from now, people will look back at these papers, mine and other people’s, and realize, ‘Oh yeah,’” she said. “Finally there’ll be enough evidence showing that these diseases are really transmitted by breathing in virus from the air.”

Then a mysterious new respiratory virus began sickening people in China at the end of 2019. Scientists quickly identified it as a novel coronavirus, but it took several more months for health agencies to acknowledge that COVID-19 spreads through air—a blip in the normally glacial pace of science but a long time in an emergency when cases are growing exponentially. Experts were initially reluctant to label the virus “airborne,” because they typically used that term to describe pathogens that linger infectiously in the air for hours, such as measles. The coronavirus doesn’t seem to last as long, but it can still transmit through the air when people talk and breathe. The smoking gun, in Marr’s view, was a study that found live viruses lingering in the air seven to 16 feet away from patients. Super-spreader events and asymptomatic spread—when people aren’t coughing or sneezing—offer additional circumstantial evidence, she said, that the virus is spreading via small aerosols from breathing and talking.

In July, she was one of 239 experts who signed an open letter to the World Health Organization outlining the evidence for airborne transmission. The WHO eventually acknowledged airborne transmission, as did the CDC, finally, in October. In retrospect, it’s remarkable how long it took to say what should be intuitive: A virus that infects the respiratory system spreads through air. “It seems like it would be obvious, right?” Marr said. A 19th-century doctor, who didn’t even know what viruses were, might have thought so too.

Still, early advice that focused on hand-washing and sanitizing surfaces has stuck, as evidenced by the hygiene theater that continues to pervade public spaces. Genuine confusion exists about the changing scientific consensus, but so does inertia. Wiping surfaces and erecting plexiglass barriers is easier than installing expensive air filters or, God forbid, reconfiguring a hermetically sealed building’s entire ventilation system. Even the CDC’s school-reopening guidelines, released just this month, said little about ventilation.

Like so many viruses before it, the coronavirus is likely to be tamed by vaccines. Perhaps soon, ventilation won’t matter again. But COVID-19 is a humbling reminder of the value of lost knowledge.

I’m writing this now at my desk, which is in front of a radiator, which is in front of a window. For apartment buildings like mine, built in the early 20th century, this is by design. The radiator runs too hot, so that residents can keep the window open for ventilation. (I am indeed too hot. The window is open.) This quirk of old building design went viral months ago in a collective “Aha!” moment. This thing that never made sense actually makes sense! Like many old buildings, my apartment has pipes that somehow always need to be repaired. I remember going downstairs one day to find a giant trench dug out in the lobby, where a steam radiator had exploded. And in the past year of working from home, I have cursed the lack of central AC and the overwhelming heat of the radiators.

But the window is open today. The air is good. This is a building designed in a time of airborne pathogens.