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LONDON: Seniors housing developers have excluded nature from the built environment. Now efforts are afoot to reverse the trend.

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, 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 West, people 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.

‘‘There was a study of more than 7300 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 them wear masks.

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 with its 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 US politicians and the offices of news outlets, killing five people and infecting 17 more.

Now, these researchers are suddenly in demand. ‘‘Our calendar is fairly full,’’ says Kevin van den Wymelenberg, director of the Biology and the Built Environment Centre at the University of Oregon. He used to receive two or three inquiries a week 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 microberelated 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 harbour deadly pathogens? Can we actually cultivate beneficial microbes in our buildings? 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 a kilogram. In recent decades our personal microbiomes have been altered by factors such as poor dietary habits, a rise in caesarean-section births, overprescription of antibiotics, overuse of disinfectants and other germ fighters, and dwindling contact with beneficial microbes on animals and in nature.

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 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.

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 travelling at up to 300km/h . A cough releases about 3000 droplets, which reach speeds of 80km/h . A simple exhale produces 50 to 5000 droplets. A person infected with influenza releases up to 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.

Facing an invisible and potentially deadly virus, the understandable impulse has been to whip out some disinfectant and go to battle. But indiscriminate bleach-bombing could backfire.

A more serious risk is that attempts to sterilise our surroundings can kill off bacteria critical for human health – or, even worse, inadvertently promote the survival and evolution of more dangerous bugs, including antibiotic-resistant superbugs. ‘‘We should be worried,’’ says Rob Knight, founding director of the Centre for Microbiome Innovation and a professor of paediatrics at University of California San Diego. ‘‘If we’re overzealously stripping off all the bacteria that would naturally be there, then we may be creating homes for bacteria and maybe even viruses that are harder to remove.’’

No amount of chemicals will get rid of everything, and what’s left behind is often undesirable. Microbiologists have swabbed the International Space Station to find out what happens inside an enclosed, supposedly sterile chamber in which every bit of food and equipment has been disinfected. As it turned out, microbes were everywhere, almost all of them human-derived.

In hopes of zapping SARS-CoV-2 straight out of the air, some building managers are installing so-called bipolar ionisation units, even though they may not work against COVID-19 and sometimes generate harmful gases such as ozone. As for the antimicrobial cleaning agents and surface coatings being applied throughout offices and other public spaces, we may be introducing large quantities of poorly understood, potentially poisonous chemicals into our everyday life – as well as speeding the evolution of disastrous superbugs.

‘‘The more we use the same antimicrobials in different contexts, the more opportunity these microbes have to develop resistance,’’ says Erica Hartmann, an engineering professor at Northwestern University who focuses on indoor microbiology and chemistry. ‘‘If they’re developing resistance to the antimicrobial itself, that’s not great, because then we’ve lost an important product in our cleaning arsenal. But if they also develop resistance to clinically relevant antibiotics, of which we have precious few, that’s an even bigger concern – and there’s evidence that both of those things happen.’’

Leung of SOM has thought about microbiology for years, but tends not to mention it to prospective clients. ‘‘If you tell a client, ‘Let’s talk about microbes’, they’ll say, ‘Get out of here – next!’’’ he says. ‘‘We have to address it carefully.’’

He says lots can be done to make buildings healthier at the microbial level. For safer air he extols the use of filters designed to eliminate SARS-CoV-2 and other pathogens and contaminants, but he cautions against bipolar ionisation technology and says air shouldn’t be sterilised over long durations. Whenever possible, Leung suggests deploying ventilation systems that pump offices full of microbially diverse outdoor air. Among his current projects is the 31-storey WeBank tower in Shenzhen, which will draw air through trees planted on balconies. ‘‘Sometimes we also open up buildings at night,’’ Leung says, noting the outdoor air is first measured for pollutants. ‘‘During the day people want airconditioning, but when they’re gone you can recharge the building with microbes from outside.’’

Proper ventilation is particularly important in energy-efficient buildings, which, like spaceships, are designed to be sealed off from the outside world. In addition to delivering fresh oxygen and eliminating the brain-numbing build-up of carbon dioxide, good airflow and filtration reduce exposure to a long list of mostly unregulated and unmonitored chemicals found indoors. These include carcinogens and endocrine disrupters in carpets, computers, freefloating dust, office chairs, paint and more.

Outdoor pollution also seeps inside buildings and gets trapped. All this means indoor air is often far worse than outdoor air.

For businesses, better air quality translates to an estimated $US6500 to $US7500 of added annual productivity per employee, mainly a result of improved wakefulness and acuity, say Joseph Allen and John Macomber, Harvard professors who coauthored the book Healthy Buildings.

Another means of achieving healthier air is humidification. Not only does sufficient moisture in the air allow the human immune system to function at its best, it also causes viral particles to drop to the floor and die more quickly. According to some calculations, viruses in dry air can survive six times as long as those in buildings with a relative humidity of about 40 per cent.

Of course, building interventions alone can’t eliminate the risk of SARS-CoV-2 contagion, so it’s best to keep social distancing and wearing masks. In the meantime, scientists are racing to develop microbial sensors for air filters, building surfaces, wastewater and even indoor air. ‘‘We have tools to help us see the unseen,’’ Van den Wymelenberg says. For now those detection tools are in their infancy.

Gilbert has ambitious plans for microbial interventions in buildings. Trained as a microbial ecologist, and with experience working on soils, plants and marine systems, he was initially sceptical when he learned the Sloan Foundation was promoting something called the microbiology of the built environment. ‘‘I thought it was a joke,’’ Gilbert says.

‘‘I’ll admit it, I thought there can’t be much microbiology in the built environment, so why would anyone be interested?’’

Then, in the winter of 2012, he got a visit from Paula Olsiewski, a program director for the Sloan Foundation. At that point he was a professor at the University of Chicago, and by the time the meeting ended, a blizzard had descended on the city. ‘‘I offered to drive her back to her hotel because I had a car that could handle the snow,’’ Gilbert recalls. ‘‘But it was snowing so heavily that the drive took 2 1/2 hours, and in that time she convinced me.’’

Now at the forefront of microbiome research, human and environmental, Gilbert was even permitted to sample president Barack Obama’s microbiome in 2016. (He’s not allowed to disclose the results.) When the pandemic hit, Gilbert quickly redirected much of his research funding toward studying SARS-CoV-2. He has one project together with Knight’s lab to see how the virus travels through hospitals, where it most often takes up residence, and whether it piggybacks on nefarious bacteria, as the influenza virus often does.

He also has a second, more counterintuitive, study under way: in an undisclosed California hospital, Gilbert is investigating whether adding harmless bacillus bacteria into medical facilities reduces the prevalence of pathogens, including multidrugresistant bacteria and viruses.

Similar studies have been done in the past, with encouraging findings, but Gilbert’s is more rigorous.

The idea of putting bacteria to work cleaning isn’t as far-fetched as it might sound. In the 1940s a Danish company called Novozymes started selling environmental microbes for decontaminating wastewater. In the 1980s and ’90s it also contracted with the US government on a largescale bioremediation project to help clean up the Exxon Valdez oil tanker spill.

About the same time, Novozymes sent researchers looking for bugs that might help clean home septic tanks, restaurant grease traps, pet stains and much more. Among their best finds were grease- and odour-cutting bacteria discovered in the outdoor grill sites of Virginia parks and the kitchen of a Florida restaurant.

Today, Novozymes is worth about $US16 billion, and its microbes are key ingredients in dozens of home-care brands. The idea is to deploy an army of microbes that eat away at dirt, debris and organic matter, also degrading the stuff left in cracks and crevices. Last year Reckitt Benckiser introduced a probiotic cleaner called Veo, which the company says will ‘‘help contribute to the balancing of the home microbiome’’.

Going a step further, scientists are studying whether salubrious environmental microbes can be introduced into urban homes to reduce the prevalence of inflammatory diseases. In Finland, one group seeded the doormats of city dwellers with about 30 grams of forest soil so residents could drag outdoor microbes inside. The six-month experiment showed the rugs did shift the indoor air to include more outdoor microbes. Next the researchers want to run a large-scale study to see whether forestsoil-impacted rugs can improve the immune systems of infants and young children. (Another Finnish group is simply smearing infants with a soil preparation to find out if there are health benefits.)

So far no one knows exactly which outdoor microbes are beneficial or how much exposure is best. Still, a number of start-ups are marketing bacteria sprays for homes and businesses. Belgium-based TakeAir advertises an ‘‘air enricher’’ that disperses soil- and ocean-derived microbes through existing ventilation systems to create ‘‘a 100 per cent natural and protective biosphere for your building users’’. Clients include a Belgian chain of gyms and a housing project in Antwerp. Another frontrunner, Betterair in Israel, sells ‘‘the world’s first organic air and surface probiotic’’, a freestanding microbe mister that retails for $525 (Refill cartridges are $130.)

It’s only a matter of time before these technologies become better understood and more widespread. ‘‘There’s absolutely fascinating research to be done,’’ Gilbert says. ‘‘I want to maybe engineer bacillus so it has properties that can stimulate the immune systems of people in a room.’’

Van den Wymelenberg is also hopeful: ‘‘There’s no reason this stuff can’t work,’’ he says. ‘‘We’re already heavily manipulating the microbes in our buildings, just not deliberately.’’

On a Tuesday afternoon in June, Leung takes my call while teaching his son to drive. Asked about the probiotic air enhancers, he laughs. ‘‘It actually says a lot about human beings,’’ he says. ‘‘We’ve created buildings so sterile that now we have to buy nature and spray it back in. That’s how silly we are.’’

Perhaps the pandemic will serve as a wake-up call. ‘‘This is our chance to right our wrongs of the past 200 years,’’ he says, speaking of restoring our relationship with soils, plants and animals. It won’t be easy. Over the next 40 years, the total amount of indoor square footage will roughly double worldwide, science journalist Emily Anthes reports in her book The Great Indoors. Given the horrors of COVID, many businesses and building managers will also strive to sanitise indoor environments like never before, perhaps causing unintended consequences.

In the meantime, the climate crisis is compounding potential health risks as flooding, wildfires and man-made disasters destroy the natural world, exposing us to dangerous new diseases while annihilating the microbes we probably need to prevent widespread chronic illness (not to mention those we may need as medicines). Already, Leung says, urban air is often depleted of healthful natural bacteria. ‘‘In the wintertime, when the leaves are gone from trees, do you know what the main thing is you find in urban air?’’ he asks. ‘‘Microbes from animal faeces.’’

Still, the pandemic may be changing our perspective on indoor life – and even physically altering our microbiomes. Although some people are cleaning too much, eating more junk food and drinking more alcohol, prescriptions for antibiotics are markedly down from last year, according to the US Centres for Disease Control and Prevention. One explanation is a decrease in non-COVID illnesses as a result of social distancing.

And though people aren’t mingling as much or sharing microbes – which can be beneficial when pathogens aren’t involved – those lucky enough to live where they aren’t required to hole up indoors are spending more time in nature. ‘‘I mean, I see neighbours outside I didn’t even know existed, and they’re working in dirt that they’re pretending is a garden,’’ one microbiome expert says. As businesses allow employees to work from home, many are also abandoning urban life for greener settings.

But winter is upon us in the US, and the pandemic is surging once again as more people move indoors. If we don’t adjust our lifestyle and start making our buildings healthier from a microbial standpoint now, Leung says, we’ll get hit even harder. ‘‘If you think this pandemic is bad, wait another 50 years, when we’ll have a much older population and much higher healthcare costs.’’

In the not-so-distant future, he warns, three interrelated factors will increasingly affect our wellbeing: climate change, chronic health problems and more pandemics. ‘‘We’re going to have to design for that,’’ Leung says. ‘‘And it’s going to be important to bring humans and nature together again – like in heaven.