The Tribune

AN infectious disease expert has suggested that air conditioning may be playing a role in the spread of COVID-19, but says ultraviolet light may be a viable source of sterilising areas where the virus is present.

Edward Nardell, a professor of medicine and global social medicine at Harvard Medical School, has been looking at insights related to tuberculosis and how ultraviolet lights have been long used to remove TB from the air.

He thinks the same could apply to SARS-CoV-2, the strain of coronavirus that causes COVID-19.

Dr Nardell, who is also a professor of environmental health and immunology and infectious diseases at Harvard T H Chan School of Public Health, said hot summer temperatures can create situations similar to those in winter when respiratory ailments usually surge - leading people to go indoors where they breathe and rebreathe air that is typically is not refreshed as it would be outside.

“The states that, in June, are already using a lot of air conditioning because of high temperatures are also the places where there’s been greater increases in spread of COVID-19, suggesting more time indoors as temperatures rise,” Dr Nardell said in an article published in the Harvard Gazette. “The same [thing] happens in wintertime, with more time indoors.”

While it has been understood that COVID-19 is mainly transmitted through large droplets expelled from talking, sneezing or coughing, Dr Nardell said evidence has risen that some cases have occurred by airborne transmission.

It occurs when COVID-19 particles in smaller droplets don’t settle out within six feet and instead hang in the air and drift on currents. Airborne transmission is thought to have been a factor in the coronavirus’ spread among members of a Washington choir, through an apartment building in Hong Kong, and in a restaurant in Wuhan, China, Dr Nardell said.

Airborne transmission would make people even more vulnerable to the virus in a closed room, Dr Nardell said, adding that in an office occupied by five people, as windows are closed and air conditioners turned on, CO2 levels rise steeply, a sign that occupants are rebreathing air in the room and from each other.

“As people go indoors in hot weather and the rebreathed air fraction goes up, the risk of infection is quite dramatic,” Dr Nardell said, adding that the data, while gathered related to tuberculosis, would apply to any infection with airborne potential.

He outlined this work in June during an online presentation sponsored by the Massachusetts Consortium on Pathogen Readiness (MassCPR).

Dr Nardell told participants that a dynamic similar to that in the US south is being played out in other parts of the world.

He noted air-conditioner sales in India where units there are designed to bring in only a small amount of outside air, which again increases transmission chances.

Ultimately, Dr Nardell maintained that being outside or increasing ventilation inside can be effective in slowing transmission, though the ventilation systems in many corporate settings limit how much fresh air can be brought in.

He recommends the use of portable room air cleaners, though they can have limited air flow. Further, germicidal lamps, a technology that Dr Nardell said is almost 100 years old, have been proven effective in protecting against tuberculosis infection and are already in use in some settings to fight SARS-CoV-2.

Compared with mechanical ventilation and portable room air cleaners, the lights, according to one study, have been shown to be up to 10 times more effective, Dr Nardell said.

The lamps are set up to shine horizontally, high in the room where sterilisation is needed.

Air currents, stirred in part by warmth from human bodies, circulate up to the ceiling, where the ultraviolet light kills floating pathogens, and then back down again.

Dr Nardell said this technology is not only proven, it can be deployed cheaply and easily in a number of settings as society reopens.

The lights are not a panacea, however, and the predominant route of transmission needs to be considered in determining whether they are appropriate, he said.

Despite the need for disinfection in nursing homes, for example, transmission there may be mainly through close contact between staff and patients, making them less-than-ideal sites for the germicidal lights, Nardell said.

“Where [the lights] should be considered in the upcoming resurgence … would be, obviously, in a health care setting, but also in public buildings such as stores, restaurants, banks, and schools,” Dr Nardell said. “We need to know where transmission is occurring to know where they should go.”

Replacing the standard filters currently in use on the return vents of central air conditioning units with HELP Filters and installation of UV lamps on the air handlers at the earliest possible opportunity may also help prevent any air transmission of the virus. The cost of doing this is relatively cheap, running to just a few hundred dollars depending on the size of the system in use.