Four years ago a doctoral student in architecture asked Luke Leung to help him come up with a thesis topic. Leung, an engineer whose projects include the world’s tallest building, the Burj Khalifa in Dubai, proposed the question: What is heaven?
“The student did a lot of research and found that no matter the faith—Islam, Judaism, Christianity—heaven is always a place with a garden and running water,” recalls Leung, director of the sustainable engineering studio of Skidmore Owings & Merrill LLP, the architectural behemoth better known as SOM. “So then we started questioning, ‘If that is heaven, what exactly is the place we are living in?’ ”
In the Western world, humans spend 90% of their time indoors. The average American spends even more than that— 93%—inside buildings or cars. For years scientists have sounded the alarm that our disconnect from the outdoors is linked to a host of chronic health problems, including allergies, asthma, depression, irritable bowel syndrome, and obesity. More recently, experts in various fields have begun studying why buildings, even those designed to be as germ-free as possible, are vectors for disease, not the least Covid-19.
“There was a study of more than 7,300 cases in China, and guess how many people caught the disease outdoors?” Leung asks. “Just two.” Early testing following Black Lives Matter protests in Minnesota also suggested that transmission of SARS-CoV-2 outside is rare, even when thousands of people gather, talking, yelling, and chanting—at least when most of those people wear masks. Out of more than 13,000 protesters tested, only 1.8% were positive. Other states showed similar results.
Leung says a “misalignment with nature” in building design is partly to blame for our scourge of chronic diseases and the current pandemic. The relative lack of air flow and sunlight is an obvious issue; temperature, humidity, and indoor air pollution also play a role. But there’s another, less discussed factor: the microbiome of the built environment, which encompasses trillions of microbes including bacteria, fungi, and viruses.
Until about 15 years ago, very few scientists—and even fewer architects, designers, and engineers—paid attention to indoor microbes, with the exception of problematic outcroppings such as black mold and legionella, the bacteria that causes Legionnaires’ disease. That changed after the 2001 anthrax attacks, when letters laced with deadly bacteria were mailed to politicians and the offices of news outlets, killing 5 people and infecting 17 more. Experts at the nonprofit Alfred P. Sloan Foundation began contemplating what role buildings might play in mitigating bioterrorism threats. Realizing we knew almost nothing about which microbes exist indoors, the foundation poured tens of millions of dollars into research. Soon scientists uncovered rich ecologies of fast-evolving indoor microbe populations. Crucially, most had little overlap with outdoor populations, including salutary species that humans co-evolved with over millions of years.
Now, with a global pandemic raging, these researchers are suddenly in demand. “Our calendar is fairly full,” says Kevin van den Wymelenberg, director of the Biology and the Built Environment Center at the University of Oregon. He used to receive two or three inquiries per week, asking for advice on how to improve the health of a building. Now he gets 20 a day. “It’s everyone from hospitals, to large commercial real estate portfolios, to nursing homes and school districts, to personal friends who run a barber shop and are trying to decide whether or not they should blow out the hair of their patrons.”
Of course, the most urgent microbe-related question is where to find SARS-CoV-2 and how to kill it. Beyond that, there are also long-term questions. How can we promote indoor microbe populations that don’t make us chronically ill or harbor deadly pathogens? Can we actually cultivate beneficial microbes in our buildings the way a farmer cultivates a field? Experts including Van den Wymelenberg are confident all this is possible. “I really believe our building operators of the future and our designers will be thinking about how to shape the microbiome,” he says.
The term “microbiome” is most often used to refer to the population of microbes that inhabit our body, many of which help produce vitamins, hormones, and other chemicals vital to our immune system, metabolism, mood, and much more. In the typical person, microbial cells are as numerous as those containing human DNA and cumulatively weigh about 2 pounds. In recent decades our personal microbiomes have been altered by factors such as poor dietary habits, a rise in cesarean-section births, overprescription of antibiotics, overuse of disinfectants and other germ fighters, and dwindling contact with beneficial microbes on animals and in nature. According a 2015 study, Americans’ microbiomes are about half as diverse as those of the Yanomami, a remote Amazonian tribe.
Like our bodies, the buildings we inhabit are also teeming with microbes. “Inhale deeply,” writes Rob Dunn, a professor of applied ecology at North Carolina State University, in his 2018 book Never Home Alone. “With each breath you bring oxygen deep into the alveoli of your lungs, along with hundreds or thousands of species. Sit down. Each place you sit you are surrounded by a floating, leaping, crawling circus of thousands of species.” Dunn says more species of bacteria have been found in homes than there are species of birds and mammals on Earth. In 2015, researchers found that indoor air contains nearly equal concentrations of bacteria and viruses. (Almost all viruses are harmless, and some may be beneficial.) Over time these many microbes have adapted to survive, and even thrive, everywhere from our pillowcases and toothbrushes to the more extreme climates of our dish washers, showerheads, ovens, and freezers.
Many are derived from humans, or likely feed off human debris. Like Pigpen from the comic strip Peanuts, each of us has a plume of microbes spewing off our body at a rate of about 37 million bacteria and 8 billion fungal particles per hour; the difference is that our plumes are invisible to the naked eye. Indoors, the impact is measurable. One study notes that it takes less than 24 hours for a hotel guest to colonize a room with their personal microbes, erasing all traces of previous guests and making the space microbially identical to their home.
Considering our perpetual emanations, it’s easy to envision how the coronavirus might spread within a room. A single sneeze discharges roughly 30,000 microbe-filled droplets traveling at up to 200 mph. A cough releases about 3,000 droplets, which reach speeds of 50 mph. A simple exhale produces 50 to 5,000 droplets. We know that a person infected with influenza releases as many as 33 viral particles per minute just breathing and about 200 million per sneeze. Meanwhile, exposure to just a few hundred SARS-CoV-2 particles may be enough to cause infection.
Outdoors our invisible plumes almost always disperse quickly, which is a very good thing in the case of Covid carriers. “Any virus that is released into the air is rapidly diluted, moved by wind currents, and spread out across a seemingly infinite space,” says Linsey Marr, an expert in infectious disease transmission and professor of civil and environmental engineering at Virginia Tech. “It’s almost like putting a drop of dye into the ocean vs. putting it into a glass of water.” Sunlight also inactivates viruses in as little as five minutes— eight minutes in the case of SARS-CoV-2. A study from the Department of Homeland Security found that the coronavirus can hang around indoors in the dark for hours.
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