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 environ