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The air man needs a fresh hit. It’s a beautiful summer morning. Dew shines on the grass. Birds chirp. What a glorious day to contemplate the air. I had con­tacted the air man—he has a name: Steven Welty—because of a faint, bizarrely sweet odor in our new house that had been annoying me for weeks. Nobody else in my family smelled it, not my wife or our kids. They just thought I was crazy, so I called Welty, thinking he could testify on my behalf. He designs airflow systems that prevent the spread of infectious diseases and potential acts of airborne terrorism in hospitals, office buildings, and high-target government buildings.

Though he doesn’t make many house calls, my problem piqued his curiosity, so here he is standing on my front lawn. Welty is bald and wiry, and he’s a fast talker. He begins many sentences with, “Dude.…” He explains that he’s virginizing his nose to my house. He had not smelled anything when he first showed up 15 minutes ago. With his nose now primed, Welty pinches his nostrils—to keep his nasal purity intact—and walks through my front door to the foyer, the area with the odor. He releases his fingers and breathes in deeply, as if he is drawing his last breath.

“Dude,” he says, “you have an epic nose.”

“What do you mean?” I say.

He explains that he can barely smell anything unusual, if at all. This is a theme in my life. As a practicing hypochondriac and obsessive worrier, I often sense danger where others sense nothing. My heart sinks.

“You can’t smell anything?” I say.

Welty says there’s an odor but it’s so faint, so barely noticeable, that people could rent my nose out, like a dog that sniffs for mold.

“Mold Dog Rosenwald,” he says. “Dude, that’s you.”

I briefly consider and reject this new and exciting career. We walk around my house looking for mold, the most typical source of household smells. We check the basement. We check an old fireplace. With flashlights we look into my HVAC system. We don’t find anything. Standing in the kitchen, making small talk about my residential air, the conversation turns to the kind of air Welty really worries about.

He tells me about the SARS outbreak in 2003 and how scientists have traced it back to a Hong Kong hotel where one man, Liu Jianlun, infected a number of other guests who then went on to spread the virus around the world. Though there has been speculation that Liu threw up in the hallway, Welty thinks the germs spread from behind his closed door on currents of air. When I express shock at how that could be, Welty introduces these phrases into the conversation: “toilet aerosolization” and “fecal cloud.” I imagine a cloud in the sky made of precipitation. Then I imagine a cloud above my toilet made of—well, I’ll stop now. I realize I can never unsee this image. He tells me about flu and how people are trying to stop it with, of all things, humidity. He tells me about so-called “super-emitters”—people who when they sneeze spread far more germs than an average gesundheit situation. He tells me about Clostridium difficile, an infection that drifts around hospitals, causing, among other symptoms, “watery diarrhea.”

At this point, I’m considering relocating to a bubble.

“I had never thought about any of this stuff,” I say.

“Dude, you have no idea what’s out there.”

So I ask him to take me on a journey through the air.

Airborne Deniers

Welty lives with his wife and son in a two-story townhouse in a quiet northern Virginia suburb, about an hour’s drive from the White House. I arrive there early one morning to pick him up for a road trip. We’re heading four hours down I-81 to Virginia Tech University to see one of his heroes, Linsey Marr, an environmental engineer who recently won a $2.3 million NIH grant to study how humidity affects the spread of influenza. But the air man is running late. At his dining room table, I find him stacking books as carry-on luggage for our trip: Airborne Infection on top of Pulmonary Deposition and Retention of Inhaled Aerosols on top of Hospital Airborne Infection Control on top of Aerosol Technology on top of The Aerobiological Pathway of Microorganisms.

The covers and spines of the books are beat up and old, like antique copies of Huck Finn found at a friends-of-the-public-library sale. They are a perfect metaphor for the study of airborne disease in this country: tattered, old fashioned, vintage. In the 1940s and ’50s, when several of the volumes were published, airborne disease transmission was a hot area of scientific inquiry. Measles and tuberculosis killed people. Penicillin and vaccines were just being developed. Public health experts centered their attention on the air. “Prevention of the institutional spread of airborne contagium should become the first objective of air hygiene,” William Firth Wells, a famous but now forgotten biologist and sanitarian, wrote in Airborne Contagion and Air Hygiene, another book in Welty’s stack. Their foresight was remarkable.

While researching this story, I managed to come down with coxsackie virus, which causes hand, foot, and mouth disease—and a really, really bad sore throat. I sent Welty an email saying how sick I was and he responded, “It’s ironic that you’re the perfect person to benefit from my expertise.” Welty told me that government scientists in the 1960s used coxsackie virus on prisoners to study airborne disease transmission. In one groundbreaking study, two sets of patients were separated by a wire barrier. One set was inoculated with coxsackie. The other wasn’t. Large floor fans were arranged to really stir things up. Everyone wound up sick. We now know that as many as 100 infectious bacteria, viruses, and fungi can be transmitted by air, either inhaled as they sail around or ingested after landing on a surface.

We now know that as many as 100 infectious bacteria, viruses, and fungi can be transmitted by air

But in the ’60s and ’70s, the growing use of antibiotics and vaccines slowly relegated the study of airborne disease transmission to benchwarmer status. “Doctors had such overwhelming success with antibiotics that they thought it was the end of disease altogether,” Wladyslaw Kowalski, an aerobiological engineer and former Penn State researcher, told me. “They no longer cared much how it was transmitted because they had the cure for everything.” Airborne disease conferences dried up and so did research dollars. Ear infection? Here’s a pill. Strep throat? Here’s a pill. Flu? Here’s a needle, roll up your sleeve. Disease prevention turned into signs in bathrooms that say, “Did you wash them? Hand washing prevents disease.” The signs are often accompanied by a smiley face.

In the last decade or so, two events have reawakened interest in the moribund field. The first was SARS. The initial outbreak at the Hong Kong hotel was bad, but the most chilling incident occurred in an apartment complex called the Amoy Gardens. There, a single man with really bad diarrhea infected 321 people, killing more than 40. Scarier still, he did it from the solitude of his own bathroom. Welty and other airborne disease specialists have pointed to either the building’s plumbing or fan system (or both) as spreading virus-laced droplets through the air, infecting unwitting neighbors who breathed the stuff as it crept through open windows on a beautiful Hong Kong night. A New England Journal of Medicine paper in 2004 pointed out, “The SARS epidemic provides an opportunity for the critical reevaluation of the aerosol transmission of communicable respiratory diseases.”

The other event rekindling interest in airborne disease transmission is the rapid and frightening—especially to hypochondriacs like me—microbial resistance to everyday antibiotics. The World Health Organization says, “A post-antibiotic era—in which common infections and minor injuries can kill—far from being an apocalyptic fantasy, is instead a very real possibility for the 21st century.” So not only are there viruses to worry about—the influenzas, measles, and rhinoviruses of the world—but air contains increasingly antibiotic-resistant forms of tuberculosis, pneumonia, and whooping cough, just to name a few.

The old way of thinking—by which I mean generally ignoring the air—still dominates

Airborne disease adherents say that even the threat of a post-antibiotic era should re-align our thinking with the pre-penicillin days, when airborne disease transmission and prevention was a more appreciated concept. In practice, however, the old way of thinking—by which I mean generally ignoring the air—still dominates. Welty and other airborne disease specialists refer to those who don’t fully embrace the potential terror lurking in ducts and vents as airborne deniers. They point fingers at even the most hallowed of institutions, including the Centers for Disease Control (CDC). The agency still publicly recommends people wash their hands to prevent the flu despite one of the great highlights of the air man’s life: In 2009, as the H1N1 virus swept through schools and nursing homes, a CDC spokesman admitted to CNN that, “We don’t have solid data on the effect that hand washing has on the transmission of H1N1.” The reason, according to virologists, is that flu isn’t stable once on your hands; it breaks down and becomes less infectious. The air is where it hides, which is why the air man loads his old books in my trunk, like Linus with his blanket, and we drive down to see Linsey Marr at Virginia Tech.

Trouble With Toilet Plumes

Interstate 81 is a scary stretch of highway packed with long-haul truckers zipping north and south. I grip both hands on the steering wheel. The air man sits next to me, periodically dipping into the back seat, where he has stashed several large portable file cabinets containing perhaps thousands of airborne disease research papers. (The books are weighing down my trunk.) Welty, who is 55 years old, came to his specialty late in life. After graduating from Wake Forest University with a degree in economics, his careers included running a Washington, D.C., limo company that used old London cabs, inventing a fat-free yogurt muffin (called the Yogin), and investigating mold in people’s homes. He is a rather obsessive person, and studying mold led him to appreciate the air, which led to collecting and reading hundreds of old books about airborne disease transmission, which led to numerous classes and certifications in indoor air and filtration. Welty has briefed top federal officials, including those at the Environmental Protection Agency, and designed a bioterrorism protection system at a secure building in Washington, the address of which he can’t disclose.

In many ways his career is possible because of how we built our modern world. Air flows around us like an unseen, living river. Yet we have constructed our homes and cities and office parks with little appreciation or understanding of it, ignorantly erecting dams, dikes, and tributaries for air with slim thought for the consequences. In the old days, fresh air flowed pretty freely through huts and homes, and the sun’s rays fried many of the bad bugs. Now most new office buildings don’t even have working windows. As homeowners, we are so energy conscious and fearful of our precious heated air escaping that we don’t allow any fresh air to come in. We just recycle the stale stuff over and over again. The germs must love what we’ve done with the place.

Air flows around us like an unseen, living river. Yet we have constructed our homes and cities and office parks with little appreciation or understanding of it

In the car, Welty and I discuss some of the papers in my back seat, which he’s also been sending me for the past few months. I tell him one of my personal favorites is “Lifting the lid on toilet plume aerosol,” a title you probably don’t want to ponder if you have someone in your house with an upset stomach. The paper summarizes dozens of studies on what happens after a sick person uses and then flushes a toilet. For purposes of metaphor, imagine a salad spinner—you cover it while spinning to stay dry. “Aerosolization can continue through multiple flushes to expose subsequent toilet users,” the paper says. “Some of the aerosols desiccate to become droplet nuclei and remain adrift in the air currents.” It is thought that Norovirus, SARS, flu, C. diff, and microbes from many other ailments poof up into the air from toilets and settle onto nearby surfaces or waft through ventilation systems.

A few weeks after our trip, I called the paper’s author, David Johnson, an environmental health professor at the University of Oklahoma. “I’m certainly more leery of public toilets,” he told me. One thinks that flushing a toilet gets rid of whatever is in it. One is wrong. After flushing toilets in a lab setting, Johnson found that bacteria are still there, potentially launching from the bowl, after 24 flushes. Closing the lid doesn’t necessarily do any good. He pointed me to a study in the United Kingdom that simulated an attack of acute diarrhea in a test toilet; it showed microbes could escape even with the lid closed. “Although splashes would probably have been contained by closing the lid,” the authors wrote, “there was a gap of 15 mm between the top of the porcelain rim and the seat, and also a gap between the seat and the lid of 12 mm, which would allow aerosols to escape into the room.”

One thinks that flushing a toilet gets rid of whatever is in it. One is wrong.

There are ethical limits on testing that have hampered many modern efforts to figure out how people are being sickened by the air. Johnson can’t sit a sick person down on a toilet at Grand Central Station and mount a modern-day coxsackie experiment, for instance. So, what should one do about the potential threat? In the case of toilets—an obvious fixation of obsessives like myself—I asked Kenneth Mead, an engineer at the CDC’s National Institute for Occupational Safety and Health. One obvious idea, he said, is to eliminate the gap between seats and lids. But this, of course, would represent a fairly significant design challenge for the toilet industry. Building engineers might also consider placing ventilation fans on the floor to suck infected air down, rather than installing overhead exhaust systems that circulate it into a rising tornado ready to be inhaled.

For that matter, designers could reexamine airflow in HVAC systems and buildings, and even down city streets. They could also consider the other primary source of transmission, the mouth, which is a quite scary weapon, particularly with flu. Werner Bischoff, an infectious disease expert at Wake Forest, published a study last year in which he sampled air in an emergency room. His team found flu virus in the air as far as six feet from an infected patient’s head. The real stunner was that of the 61 patients with flu, five of them emitted significantly more virus than the others. Bischoff called these people super-emitters and he suspects they are responsible for 80 percent of infections. The problem, Bischoff told me, is that there is currently no way to know who these super-emitters are or how to stop them.

That’s where Linsey Marr’s work might help, particularly during nasty flu seasons, which the CDC has decreed this one to be (the dominant strain is especially virulent). Scientists studied humidity in the golden days of airborne disease inquiry, but it’s only in the past five years or so that Marr and other researchers have taken it up seriously again. The research is difficult because it involves not just biology, but chemistry, aerosol science, and industrial engineering. The research-industrial complex tends to keep subject areas segregated, making funding and collaboration difficult. Marr is unusual in that she has managed to recruit researchers with biology and chemistry backgrounds to her lab.

After a couple stops for coffee, muffins, and beef jerky (I cannot make a road trip without some), we arrive at Virginia Tech. Marr meets us outside her lab building. She is tiny and perky and ready to chat about air. It’s lunchtime, so she suggests we walk a few blocks to a sushi restaurant, which doesn’t seem like a great place to potentially discuss fecal clouds, but really, is there a good place? We find a corner table and order drinks. Welty and Marr bond.

“There are tons of airborne deniers,” Welty says.

“It’s all about washing your hands,” Marr replies.

Marr, who is 40, became interested in the air as an undergraduate at Harvard; during runs along the Charles River she wondered what the smog was doing to her lungs. These days she has young children whom she sends to day care (the epidemiological equivalent of a war zone). Even though the teachers are obsessive about cleaning surfaces and washing hands, Marr noticed that it seemed to have little effect on pathogen transmission. “My kids were getting sick all the time, so I started reading the scientific literature,” she says after we order our sushi, “and I was really surprised how little is actually known about it.”

A sushi restaurant doesn’t seem like a great place to potentially discuss fecal clouds, but really, is there a good place?

Marr decided to run a series of experiments. In one, she collected mucus from a 1 month old, her daughter, and added flu viruses to it. She kept the samples at various humidity levels. Below 50 percent humidity—your average heated building in wintertime, without a decent humidifier—the mucus dried up but the virus survived quite well in the air. But above 50 percent, the virus became inactive. The droplets didn’t fully evaporate, leaving a mixture of virus and mucus that’s too salty or too acidic to survive for long.

So, I ask, “What should schools be doing?”

Schools should increase their humidity, she says, as should hospitals. “If you keep humidity in a certain range, I think you could probably cut down transmission by a lot.” But that work is tricky: Older studies have shown that dryer air prevents the spread of other viruses, such as the common cold. Marr needs to figure out exactly how far to turn the dial.

Marr then mentions another study she’s working on, this one about how viruses settle to the floor as dust.

“What does that mean?” I ask.

“That means a sick person could have cleared out of the room, along with the air, but if the person was coughing and sneezing and stuff, the virus might have settled on the floor. New people come in, they walk around, and they kick up the dust.”

I suddenly wonder if any air is safe.

Marr brings up her husband, who is 6 foot 2 and rarely falls ill.

“The kids get sick all the time, and I get sick whenever they’re sick. And so I’m thinking he’s up there breathing air that we don’t—maybe the viruses that we pop out don’t get up to his nose because they all kind of settled out,” she says. “So I had this hypothesis that maybe shorter people get sick more often because they’re exposed to more viruses resuspended from the floor. We want to go do measurements now to see if this really exists.”

I ask what her husband thinks of that.

“He is skeptical,” she says. “He just thinks he has a different immune system or something.”

Out Of Sight, Out Of Mind

A few months after our trip to Virginia Tech, Welty drops by my house one weekend. We are looking again for the odor, which my wife now acknowledges might possibly exist (or at least does not want to argue about anymore). We rented a portable olfactometer and I’m on the floor wearing a mask and sniffing around. The mask is attached to an oxygen tank that pipes in fresh air. The idea is if I locate something funky, I’ll know because it will overtake the fresh oxygen. I don’t find anything, and that, I realize, sums up the predicament with air: Though it is all around us, we can’t easily see what’s in it. So as a society, we ignore it. Before I met the air man I had not spent any significant time pondering the air. Neither had my wife, and she’s a family doctor, whose business is to protect people from sickness.

There are tools to fight airborne disease, of course, but they are fewer than you’d expect and relatively arcane. When Welty is hired, for example, he often recommends ultraviolet lights (UV) in HVAC systems to cook microbes as they pass through. But even these systems are not perfect, and they can be prohibitively expensive. Some hospitals are beginning to send robots into recently vacated rooms to flash-fry every surface with intense pulses of UV light. Certain companies are now pushing ventilation systems that mix in natural air, but those, again, are not cheap.

When Welty first came to my house, he lent me a cold plasma system for my HVAC system—a tiny box with two sticks the size of crayons sticking out. One generates positive ions, the other negative. As air passes by, the electrical charge attracts microbes and, according to the manufacturer, robs them of hydrogen, killing them. We also installed a UV light. The devices haven’t yet eliminated the odor—at this point, we’re considering replacing the hardwood floors—but my wife and I have noticed fewer colds.

Welty is under no illusion that such measures are a panacea, rather, they are Band-Aids on a larger problem. What people like he and Marr want is a full-scale appreciation for the dangers of airborne disease transmission and how we might deal with them.

Right now that’s a lonely conversation. Down at Virginia Tech, as we get ready to hit the road, Welty invites Marr back to my car so he can show her all of his books. I open the trunk and she says, “It’s like a traveling library.”

“Have you seen this one?” Welty says, holding The Aerobiological Pathway of Microorganisms.

“That’s a classic,” Marr says.

He shows her a collection of papers from an old airborne conference in the 1960s. She’s impressed he has original copies.

“They were having conferences on this stuff up until, like, 1980,” he says.

“And they just stopped,” she says.

And then he hands her a gift: An Introduction to Experimental Aerobiology, published in 1969.

He inscribes it, “To my fellow airborne believer.”

How The Flu Causes Infections

Influenza, like most airborne pathogens, must endure a perilous journey as it travels between hosts. When the virus leaves the body, it is encased in fluid. That droplet must be small enough that it can be carried by air, but large enough that its protective shell of moisture won’t evaporate away entirely—because if the virus dries out, it will likely die. Here’s how influenza strikes that delicate balance to infect up to one in five people in the U.S. each year.—Katie Peek

1. Sneeze

A person with the flu sheds infectious particles by showering, making a bed, using the toilet, or simply walking around. But expiration—sneezing, coughing, and breathing—is the most effective way to spread the virus. In addition to creating protective droplets of moisture, a sneeze hurls those droplets into the air at high speed, spreading them far and wide.

2. Aerosolize

For an expired droplet to travel (instead of just falling to the floor), it needs to be small. And that’s where humidity comes in: On a dry day, a large droplet will evaporate as it falls, becoming small enough to aerosolize. On a swampy summer day, that same droplet will settle to the ground, limiting its ability to infect a new host.

3. Disperse

Air laden with droplets of flu-bearing mucus sails through ventilation ducts, classrooms, and airplane cabins. Dispersal becomes a race against time: Influenza can stick around for a while but it is damaged by heat, light, and ozone (and that’s provided it survived the initial stress of being coughed up).

4. Land

The viral pathogens must land on their host—a step epidemiologists call exposure—in sufficient numbers to actually create a new infection. That process can be helped along if the virus lands on a mucus membrane—like inside the lungs, on the eyelids, or in the mouth.

5. Infect

If the flu has reached its new host in numbers sufficient enough to initiate an infection, potential victims have a few last chances: A strong immune system, antibodies from a previous infection, and vaccines can all ward off the virus. But if those lines of defense fail, the chills and fever will set in, and with every sneeze the transmission cycle will begin anew.

How Can Humankind Fight Back?

Vaccines and medicines are one approach, but it’s also crucial to understand precisely how flu spreads. Amir Aliabadi is a mechanical engineer whose research into the mechanics of sneezing led him to build a sneeze machine at the University of British Columbia. He thinks experiments in hospitals and other hotbeds of infection could help reduce transmission. Occupational hygiene workers, for example, could use the results to better arrange beds in a hospital. Laboratory studies are too simplistic, Aliabadi says. “This ties into fluid mechanics, biology, epidemiology, and building design. It’s a very hard problem.”

This article was originally published in the February 2015 issue of Popular Science, under the title “Take A Deep Breath”.

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