Continuous low doses of far ultraviolet C (far-UVC) light can kill airborne flu viruses without harming human tissues, according to a study at the Centre for Radiological Research at Columbia University Irving Medical Centre (CUIMC). The findings suggest that use of overhead far-UVC light in hospitals, doctors’ offices, schools, airports, airplanes, and other public spaces could provide a powerful check on seasonal influenza epidemics, as well as influenza pandemics.
Scientists have known for decades that broad-spectrum UVC light, which has a wavelength of between 200 to 400 nanometres, or nm), is highly effective at killing bacteria and viruses by destroying the molecular bonds that hold their DNA together. This conventional UV light is routinely used to decontaminate surgical equipment.
“Unfortunately, conventional germicidal UV light is also a human health hazard and can lead to skin cancer and cataracts, which prevents its use in public spaces,” said study leader Dr David J Brenner, the Higgins professor of radiation biophysics, professor of environmental health sciences and director of the Centre for Radiological Research at CUIMC.
Several years ago, Brenner and his colleagues hypothesised that a narrow spectrum of ultraviolet light called far-UVC could kill microbes without damaging healthy tissue. “Far-UVC light has a very limited range and cannot penetrate through the outer dead-cell layer of human skin or the tear layer in the eye, so it’s not a human health hazard. But because viruses and bacteria are much smaller than human cells, far-UVC light can reach their DNA and kill them,” he said.
In their earlier studies, Brenner’s team demonstrated that far-UVC light was effective at killing MRSA (methicillin-resistant S. aureus) bacteria, a common cause of surgical wound infections, but without harming human or mouse skin.
Influenza virus spreads from person to person mainly through fine liquid droplets, or aerosols, that become airborne when people with flu cough, sneeze, or talk. The new study was designed to test if far-UVC light could efficiently kill aerosolised influenza virus in the air, in a setting similar to a public space. In the study, aerosolised H1N1 virus – a common strain of flu virus – was released into a test chamber and exposed to very low doses of 222 nm far-UVC light. A control group of aerosolised virus was not exposed to the UVC light. The far-UVC light efficiently inactivated the flu viruses, with about the same efficiency as conventional germicidal UV light.
“If our results are confirmed in other settings, it follows that the use of overhead low-level far-UVC light in public locations would be a safe and efficient method for limiting the transmission and spread of airborne-mediated microbial diseases, such as influenza and tuberculosis,” said Brenner.
At a price of less than $1,000 per lamp – a cost that would surely decrease if the lamps were mass produced – far-UVC lights are relatively inexpensive. “And unlike flu vaccines, far-UVC is likely to be effective against all airborne microbes, even newly emerging strains.”
Airborne-mediated microbial diseases such as influenza and tuberculosis represent major public health challenges. A direct approach to prevent airborne transmission is inactivation of airborne pathogens, and the airborne antimicrobial potential of UVC ultraviolet light has long been established; however, its widespread use in public settings is limited because conventional UVC light sources are both carcinogenic and cataractogenic. By contrast, we have previously shown that far-UVC light (207–222 nm) efficiently inactivates bacteria without harm to exposed mammalian skin. This is because, due to its strong absorbance in biological materials, far-UVC light cannot penetrate even the outer (non living) layers of human skin or eye; however, because bacteria and viruses are of micrometer or smaller dimensions, far-UVC can penetrate and inactivate them. We show for the first time that far-UVC efficiently inactivates airborne aerosolized viruses, with a very low dose of 2 mJ/cm2 of 222-nm light inactivating >95% of aerosolized H1N1 influenza virus. Continuous very low dose-rate far-UVC light in indoor public locations is a promising, safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.
David Welch, Manuela Buonanno, Veljko Grilj, Igor Shuryak, Connor Crickmore, Alan W Bigelow, Gerhard Randers-Pehrson, Gary W Johnson, David J Brenner