A quartz UV germicidal lamp is used to disinfect a train at the Sviblovo station of the Moscow Metro transit system. Sergei Karpukhin/Tass via Getty Images
High up near the ceiling, in the dining room of his Seattle-area restaurant, Musa Firat recently installed a "killing zone" — a place where swaths of invisible electromagnetic energy penetrate the air, ready to disarm the coronavirus and other dangerous pathogens that drift upward in tiny, airborne particles.
Research already shows that germicidal UV can effectively inactivate airborne microbes that transmit measles, tuberculosis and SARS-CoV-1, a close relative of the novel coronavirus.
"I thought it was a great idea, and I want my customers to be safe," Firat says.
As the U.S. grapples with how to interrupt the spread of the highly infectious virus, UV is being used to decontaminate surfaces on public transit and in hospitals where infectious droplets may have landed as well as to disinfect N95 masks for reuse. But so far using this technology to provide continuous air disinfection has remained outside of most mainstream, policy-setting conversations about the coronavirus.
Experts attribute this to a combination of factors: misconceptions about UV's safety, a lack of public awareness and technical know-how, concerns about the costs of installing the technology, and a general reluctance to consider the role of aerosols in the spread of the coronavirus.
Aerosols are microdroplets that are expelled when someone exhales, speaks or coughs. Unlike the larger and heavier respiratory droplets that fall quickly to the ground, aerosols can linger in the air for long periods of time and travel through indoor spaces. This process is also called "airborne transmission."
It's already recognized that the coronavirus can spread through aerosols during medical procedures, which is why health care workers are advised to wear respirators, such as N95 masks, that filter out these tiny particles. Yet there is still considerable debate over how likely someone is to spread the virus in other settings via aerosols.
Recently, the question of airborne transmission gained new urgency when a group of 239 scientists called on the World Health Organization to take the threat of infectious aerosols more seriously, arguing the "lack of clear recommendations on the control measures against the airborne virus will have significant consequences." In response, WHO acknowledged the possibility that airborne transmission "cannot be ruled out" in some public settings that are "crowded, closed, poorly ventilated." WHO officials conceded that more research is needed but maintained that most infections do not happen this way.
As the science continues to evolve, UV could emerge as an attractive safeguard against airborne transmission — one with a track record against previous pathogens — that can be deployed to cut down the risk of infectious aerosols accumulating in indoor settings such as schools, public buildings and businesses.
At Marlaina's restaurant, diners will only encounter two visible clues of the UV disinfection system installed while the restaurant was closed during Washington state's lockdown: a subtle glow of blue light above the black grates of the drop ceiling, and a posted sign at the door, proudly announcing to diners: "Coronavirus Disinfected Here!"
At the restaurant, ceiling fans circulate the air, eventually pushing any suspended viral particles that have accumulated in the dining space through the grated drop ceiling, to the area where UV lights, positioned horizontally, blast them with radiant energy.
The inspiration and technical assistance for Marlaina's owner came from a customer, Bruce Davidson, a pulmonary physician who was Philadelphia's "tuberculosis czar" in the mid-'90s. Back then, the U.S. was grappling with a new outbreak of TB that included strains resistant to existing drugs.
"Preventing transmission was the most important part, because we had no drugs, no vaccine," recalls Davidson, who now lives outside Seattle. UV light proved to be a key strategy back then, and Davidson thinks it can help again: "It really ought to be in most indoor public spaces now."
Bruce Davidson, a pulmonary physician, oversaw Philadelphia's tuberculosis control program during an outbreak of drug-resistant TB in the 1990s. One time-tested, infection-control approach that Philadelphia and other cities used was installing ultraviolet lamps near the ceilings in TB clinics and other high-risk settings.
To demonstrate the concept, Davidson lit a cigar inside Marlaina's and showed how the smoke danced upward, collecting in the ceiling space with the UV fixtures.
"If somebody has undetected coronavirus and doesn't eat with a mask and is talking and so on, the vast majority of their particles are going to get pulled up there into the killing zone and circulate and bounce around," Davidson says. "Statistically, the risk to other people is going to be very low."
Research shows close to 90% of airborne particles from a previous coronavirus (SARS-CoV-1) can be inactivated in about 16 seconds when exposed to the same strength of UV as in the restaurant's ceiling. Other types of viruses, such as the adenovirus, are more resistant and require a higher dose of UV.
"Although it's not perfect, it probably offers the best solution for direct air disinfection" in the current pandemic, says David Sliney, a faculty member at Johns Hopkins University and longtime researcher on germicidal UV.
When used with proper ventilation, upper-room GUV is about 80% effective against the spread of airborne tuberculosis, according to several studies. This is equivalent to replacing the air in an indoor room up to 24 times in an hour.
But it could be an uphill battle, Sliney says, because in the U.S., interest in using UV for air disinfection has waned in recent decades as scientists focused their attention on powerful vaccines and drugs to deal with infectious diseases.
Understanding the role of aerosols and airborne transmission
UV can be a powerful weapon against an airborne virus, but it can only go so far.
For one thing, people can still get sick from the larger, heavier droplets ejected via coughs and sneezes. They can directly inhale those larger droplets or touch a surface contaminated with them, and then touch their eyes, nose or mouth.
UV also does not prevent someone from being exposed to infectious aerosols that have just emerged from an infected person — and are lingering quite near his or her body — what researcher Richard Corsi describes as the "near field."
"In that scenario, you're inhaling a very concentrated cloud of these tiny particles that you can't see if we're close together," said Corsi, dean of the Maseeh College of Engineering & Computer Science at Portland State University. "You're getting a pretty significant dose in your respiratory system."
So, even if there is upper-room UV in a building, Corsi says face masks and social distancing are still necessary to block larger respiratory droplets and remove some of the aerosols in the "near field." But Corsi says there's now enough evidence to show that coronavirus aerosols can hang around in the air and spread throughout a room ("the far field"), and it's time to take that airborne spread seriously.
Corsi says public health authorities downplayed that risk early in the pandemic, and that worries him: "That put the public at maybe a little bit too much ease and people kept going to busy restaurants where there's lots of people in poorly ventilated environments," he said.
Corsi and Shelly Miller, a professor at the University of Colorado, Boulder, both signed onto the letter calling for WHO to update its guidance on airborne transmission.
"We have a strong degree of certainty that it plays a significant role when certain conditions are met," Miller says. "So that's crowded indoor spaces with inadequate ventilation, many people are not wearing a mask, and they're talking loudly and you're there for a long time."
One of the most alarming examples, cited by the group, was a study of a restaurant in China at which some diners seated apart contracted the virus despite never coming into close contact. Another piece of evidence came from a March 10 choir practice in Mount Vernon, Wash., after which the majority of singers contracted the coronavirus, even though they took some precautions to stay a few feet apart. The WHO letter also notes that MERS, another coronavirus that is similar to the novel coronavirus, can spread through aerosols, and "there is every reason to expect that SARS-CoV-2 behaves similarly."
In a recent publication, Miller and other experts suggest increasing ventilation, using high-efficiency particulate air filters and installing upper-room germicidal ultraviolet in poorly ventilated environments where transmission is more likely.
"What we really need in an outbreak is to have a lot of outside air that will dilute any airborne concentrations of the virus," Miller explains. "You can't necessarily go into buildings and retrofit them with a new ventilation system. But you can bring in high-powered air purifiers and hang UV lights."
Miller, who has studied GUV, describes it as an effective tool that should now be considered for a variety of settings, such as schools, nursing facilities, jails and homeless shelters.
A recent paper from Spain, authored by experts in virology, aerosols and architecture, came to a similar conclusion, saying UV is the most affordable and deployable technology for reducing the spread of the coronavirus, both to disinfect high-touch surfaces and the interior air.
A time-tested yet still misunderstood technology
Germicidal UV harnesses a portion of the electromagnetic spectrum that contains short waves of radiant energy, called UV-C. This wavelength is further away from the visible spectrum than other forms of UV light, which reach the Earth from the sun.
Think of it like giving the virus a lethal sunburn.
In the mid-1930s, William Wells first demonstrated UV could inactivate microorganisms that were suspended in the air. He later installed the technology in schools outside Philadelphia to prevent the spread of measles. It was widely used in the 1950s and '60s in health care settings and gained renewed attention during the U.S. outbreak of drug-resistant tuberculosis, when it was placed in some TB clinics and homeless shelters. It's still used in other parts of the world such as Africa, Asia and South America, where drug resistant TB is a particular problem.
Germicidal UV is also a common method of clearing germs from public water supplies, but that requires a much higher dose of UV (more watts) than what's used for disinfecting the air.
"We have very little practical experience to show how effective it can be [in a pandemic] since it's been out of use in this country and in Western Europe," said Sliney of Johns Hopkins, who chairs a committee with the Illuminating Engineering Society, which recently released new guidance on GUV.
Sliney recommends installing UV in big-box stores, restaurants and grocery stores, which typically have high ceilings. "There needs to be vertical air exchange," he adds, such as ceiling fans, so "it's not just sterilizing the air in the upper space of the room."
GUV is sometimes seen as "an orphan technology" because it straddles the fields of optical engineering, interior architecture and infection control, says Dr. Edward Nardell, a professor at Harvard Medical School who is a GUV researcher.
"It's a well-proven, extremely safe technology that is underused and often misunderstood," Nardell says. "No one doubts the efficacy of germicidal UV in killing small microorganisms and pathogens. I think the bigger controversy, if there is any, is misperceptions around safety."
Low-dose germicidal UV can damage the eyes and the skin, but Nardell says those risks can be avoided if the appropriate guidelines are followed.
While international guidelines warn against directly exposing humans to UV-C, the risks of skin cancer are considered negligible, especially compared with longer wavelengths of UV that can penetrate more deeply.
Yet Nardell says the perception that UV is dangerous has persisted for decades, making it difficult to drum up more support for the technology.
Could UV make a comeback?
Installing UV light is an investment in infrastructure. It requires finding the appropriate lamps and fixtures, getting enough air circulation and ensuring that UV does not hit people below.
Since the 1980s, Nardell and his colleagues have worked on how to deploy GUV more widely, including using "louvered fixtures" in rooms to shield people below. These do work but reduce efficiency, because most of the UV generated is blocked. Another approach devised by Nardell is an "egg crate" or gridded ceiling (like the one used at Firat's restaurant in Washington state) that lets air ascend into the killing zone but prevents any UV light rays from pointing down into the room.
"The problem is that creating an egg crate ceiling isn't simple," Nardell says. "You have to really pick and choose the places where you're going to try and stop transmission because you can't do it everywhere."
Buildings with high ceilings are more straightforward because the UV can be mounted away from humans, with shielding. To be effective, UV light must directly hit the virus or microorganism. Any impediments or even shade will block the effect.
And yet once they are installed, germicidal ultraviolet lighting systems provide a permanent and efficient means of disinfection.
A major challenge to rolling out the technology during the pandemic is not only limits on the supply chain but a lack of standardization among manufacturers and no clear mechanism for quality control.
"There has been a kind of regulatory abyss," says Jim Malley, a professor at the University of New Hampshire who studies public health and disinfection. "The average consumer would have no way of telling what's cool or crap."
With demand for UV now soaring, Malley says he's concerned about shoddy products on the market and exaggerated claims about their effectiveness against the virus.
Consumers should be wary of marketing claims about "UV wands" that can be waved quickly over surfaces or special "portals" that people walk through, he says, because those are probably not correctly calibrated to inactivate the virus and could be dangerous.
Malley says he doesn't think there's much of a viable market for upper-room GUV outside health care settings, but he supports installing the technology in the most high-risk settings, such as meatpacking plants and nursing facilities.