With Covid-19 restrictions easing and people returning to restaurants, bars, and shopping malls, a new strategy is emerging to protect us: creating an antiviral infrastructure. While we can’t completely de-germ our indoor environment—everyone should still wear masks and practice social distancing—some researchers are proposing that antimicrobial materials and techniques could add a layer of safety. Scientists are exploring germ-killing coatings that could be applied to handrails and doorknobs, doing viral swabs in workplaces and public spaces to detect germs, and installing UV lighting, which already is disinfecting air and surfaces in subway cars and buses, airport security checkpoints, and office buildings.
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But first, some caveats. Scientists still don’t fully understand Covid-19’s transmission—how much risk there is in touching surfaces and then one’s face, or how long the virus persists in aerosols. And while we know how to kill microbes on surfaces, using mists of Lysol spray and buckets of bleach (do not ingest these, please), disinfecting a public space once doesn’t keep it germ-free for long. Each person who has Covid-19 can re-seed rooms with the virus, even if they don’t know they have it.
After all, wherever humans go, we bring with us an ecosystem of germs. To show how easily microbes can spread in a workplace, environmental microbiologist Charles Gerba and his University of Arizona colleagues put Glo Germ, a fluorescent resin visible only under black light, on doorknobs, a water fountain handle, and other commonly touched surfaces in three offices. By the end of the day, almost nine out of 10 of the office workers ended up with the tracer on their hands, and 82 percent of them transferred it to other surfaces. The researchers followed five workers home, and within 20 minutes found the tracer on home doorknobs, light switches, countertops, and other surfaces, showing the potential for infectious spread.
In a 2019 study, Gerba and his colleagues seeded doorknobs with a tracer phage—a virus that attacks bacteria but doesn’t affect humans—and similarly found rapid spread. After disinfecting commonly touched surfaces and encouraging the office workers to use hand sanitizer, detection of the tracer dropped by 85 percent.
Lately, Gerba has been testing the effectiveness of an antimicrobial coating—a disinfectant combined with a polymer that lasts up to three months. The chemical in the surface coating is quaternary ammonia, one of the most commonly used disinfectants; Gerba tested a product called SurfaceWise2, but other similar products are also available. “Fortunately, most of the pathogens are not suited to long-term survival in the environment,” says Gerba. “What we’re doing really is reducing their survival time, and that reduces the probability that they’re going to be transmitted from one person to the next.”
In a 2019 study, he found the temporary coating reduced hospital-acquired infections by 36 percent, and in a preprint study (not yet reviewed by other scientists or accepted by a journal) Gerba and lead author Luisa Ikner, a University of Arizona microbiologist, found it reduced the surface concentration of a common cold coronavirus by 90 percent within 10 minutes and 99.9 percent within two hours. (Both studies received support from the manufacturer of the coating, although the authors noted that the company didn’t control the analysis or write-up.) Gerba now plans to repeat the study using the SARS-CoV-2 virus.
A major advantage of such products, says Gerba, is that long-lasting coatings would be applied by trained workers wearing protective gear, reducing the rampant spraying of disinfectants. (Inhaling cleaning products can cause eye or throat irritation.) The New York City Metropolitan Transit Authority is already testing several long-lasting disinfectants on its subway cars. Still, antimicrobial coatings have gotten a mixed reception from hospital officials, who often cite the need for more evidence that the surface materials reduce transmission.
Toxicologist Linda Birnbaum would be happy to see less disinfectant spray lingering in the air. Much of it probably isn’t necessary, she says, since soap and water are very effective at inactivating the virus. But Birnbaum, former director of the National Institute of Environmental Health Sciences, also wonders what happens to the long-lasting quaternary ammonium coatings over time. Does any of it become dust that we could breathe in? “Before we move to incorporate some of these disinfecting compounds on surfaces and building materials, it would be nice to know what actually happens to them when they’re in an environment with people,” she says.
In hospitals, surface contamination is an ever-present concern as health care workers take precautions to avoid transmitting infections from one patient to another. But in the community, the benefit of all our wiping, spraying, fogging, or coating of commonly touched surfaces is less clear. The virus can be spread from contaminated surfaces, but there’s no evidence that it is a major route of transmission, compared with breathing in viral particles. “In our great zeal for perfection, we may be solving a problem that is of minimal importance,” says Martin Blaser, an infectious disease physician and microbiologist at Rutgers University in New Jersey and an expert on the human microbiome, the diverse collection of microbes that live on and in the body.
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There’s another strategy to disinfect the air in public spaces: ultraviolet light, which has a germ-killing history stretching back more than a century. Ultraviolet radiation lies just below the visible light spectrum. (UV lamps produce a blue glow only because a bit of visible light escapes their filters.) The ultraviolet rays we block with sunscreen are the longer wavelengths of the UV range, known as UVA and UVB, which cause sunburn, skin aging, skin cancer, and eye damage. The type we use in lighting, UVC, has the shortest wavelength in the UV range and is blocked by the Earth’s atmosphere. A natural germicide, it damages the genetic material in bacteria and viruses, but because it doesn’t penetrate the skin as deeply, it is significantly safer than UVA and UVB. Some hospital systems irradiate rooms with UV lighting after patients are discharged to combat drug-resistant pathogens, and water treatment systems often use UV disinfection to make drinking water safe. (Again, like disinfectants, UV light is meant for surfaces and air, not for your insides, no matter what the president may have said.)
In one example of a study showing UVC’s power, Edward Nardell, a pulmonologist at Brigham and Women’s Hospital in Boston, placed wall- and ceiling-mounted UV lights in a tuberculosis ward in South Africa. The UV lights were turned on every other day, and two colonies of 90 guinea pigs were exposed either to only untreated ward air or UV-treated air. The guinea pigs breathing the UV-treated air had 80 percent fewer tuberculosis infections.
Nardell, a global health professor at Harvard University, is now working with the Start Coalition, an alliance of academic and global health organizations, using the lessons learned from the fight against TB to add a layer of safety against Covid-19. The first project, Start OKC, is launching in Oklahoma City with private philanthropic funding and will include placement of UV lighting in stores and other public spaces, as well as Covid-19 testing and contact tracing at outbreak hot spots. The UVC lights installed on ceilings can disinfect circulating air. If positioned properly, the lighting also could continuously disinfect surfaces, Nardell says. “You could envision that shopping carts might be under a blanket of UV so that when you take a shopping cart, you’d be very certain that it would not be infectious,” he says.
If you’re tempted to buy your own UVC lamp, be aware: Lots of gadgets promise to kill germs, including handheld devices that claim to sanitize your stuff in 10 seconds. “Some folks kind of view it as a magic wand or a lightsaber out of Star Wars. You take your UV wand and you wave it over your garbage bag,” says Jim Malley, an environmental engineer specializing in UV at the University of New Hampshire. “That’s unfortunately a gross oversimplification.”
How well UVC kills microbes depends on where it is positioned, how intense it is, and how long the space is exposed—that’s why a weak wand you buy on Amazon might not do much to protect you. But intensity also creates potential for harm; looking directly at a UVC light can cause temporary but painful eye damage.
Far UVC—a shorter wavelength than traditionally produced by UVC lamps (222 versus 254 nanometers)—is emerging as a potentially safer version. It kills microbes but poses less risk from exposure because it’s less capable of penetrating the outer layer of dead skin or the tear layer on the surface of the eye. In a 2018 study, physicist David Brenner, director of the Center for Radiological Research at Columbia University, generated influenza droplets similar to the ones released when we breathe or cough, and he showed they could be inactivated with a low dose of far UVC. He found a similar result with common coronaviruses, as he reported in an April preprint article.
Brenner envisions far-UVC lamps as tools to make airports and airplanes safer. If UVC lamps had been positioned to clear the air around travelers, he says, “perhaps we could have prevented or limited this Covid-19 pandemic.”
Stopping Covid-19 now that it is in 93 percent of the nation’s counties is much more daunting. The CDC notes that the virus can stay viable on surfaces for hours to days, and someone with Covid-19 can spew contagious droplets and possibly smaller aerosols when they talk or cough, but scientists don’t know how long the air remains infectious. With incomplete information about the hazards of transmission, “one downside is that these approaches won’t work at all, that they are maybe targeting the wrong places,” says Blaser, the Rutgers infectious disease researcher.
Architect Kevin Van Den Wymelenberg has a strategy to figure out where we might be exposed to the virus. He has just launched a project to test buildings for SARS-CoV-2 by swabbing surfaces, air filters, and air return grills. It’s like doing a health check for the spaces we occupy. Van Den Wymelenberg began by testing buildings at the Oregon Health & Sciences University and the University of Oregon, where he directs the Biology and the Built Environment Center. The sampling may help university officials monitor the campus when it eventually reopens. (Similar environmental surveillance projects have been launched by other groups to swab subways and hospitals.)
Van Den Wymelenberg also plans to offer a testing service to building owners and managers as a way to diffuse anxiety about public spaces and to track outbreaks. Initially, a kit and the processing to test 12 sampling sites will cost $2,500; Van Den Wymelenberg hopes other universities around the country will join the project, which may lower overall costs. “You can’t test every person every day,” he says. “But comparatively, it’s an order of magnitude easier to test the air handler. You might gain knowledge of 100 people with that one swab.”
Van Den Wymelenberg also has advice about making buildings safer that goes beyond killing germs. The things that enhance our indoor space—fresh outdoor air, sunlight, filtration, and ventilation—also reduce transmission risk. You can diffuse the concentration of a virus in the air just by opening a window, he says. If that’s not possible, HVAC systems can bring in more outdoor air and, ideally, exhaust the air at the ceiling. Keeping indoor humidity in a range between 40 and 60 percent also makes it harder for the virus to spread, he says.
Breathing healthier air in the office—that’s a strategy to lower our chance of catching something from a coworker, whether it’s Covid-19 or just the common cold.
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