“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, 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 per cent of their time indoors. 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 least COVID-19.

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 mould 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 five people and infecting 17 more.

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.”

Like our bodies, the buildings we inhabit are also teeming with microbes. 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 dishwashers, showerheads, ovens and freezers.

For businesses, better air quality alone translates to an estimated $6500 to $7500 of added annual productivity per employee, mainly a result of improved wakefulness and acuity, say Joseph Allen and John Macomber, Harvard professors who in April published the book Healthy Buildings.

Another means of achieving healthier air is humidification. “Most of our commercial buildings in the US are not humidified,” Leung says. “And that’s why the pandemic could get even worse this winter.”