By Alison McCook

At a hospital in Wuhan, China, a group of investigators swiped swabs over high-touch areas such as trash cans, bed handrails and computer mice, all of which tested positive for the virus that causes COVID-19. Perhaps most concerning, traces of the SARS-CoV-2 virus were present in the air.

Like influenza, COVID-19 is transmitted by respiratory droplets, which can linger in an enclosed space for more than 10 minutes. A patient who asks for a glass of water in a crowded hospital hallway can generate thousands of droplets per second. What happens to the person without a mask who steps into that air space?

Fortunately, hospitals have spent centuries improving infrastructure to prevent airborne transmission of other potentially deadly pathogens, such as the virus that causes measles, which can float in the air for up to two hours after an infected person coughs or sneezes. That infrastructure includes an intricate web of air filters and strict practices when treating patients who have (or may have) a contagious disease, with special attention paid to where procedures can generate droplet-rich aerosols.


Preventing airborne transmission of deadly diseases in hospitals “is a huge concern,” Michael J. McDavid, a technical sales representative for Professional Abatement and Remediation Technologies (PART) LLC, said. Although some hospitals are taking extra precautions because of COVID-19, he said he is “cautiously optimistic” that the same techniques that reduce the risk for measles, tuberculosis and other contagious diseases will also work for COVID-19. For companies like his, which have worked for years on air quality in health care settings, the new coronavirus is “just another pathogen we’re dealing with now. Nothing else has changed.”

For a symbol of the fight against airborne transmission in hospitals, look no farther than Florence Nightingale, who advocated in the 1800s that facilities should take steps to improve ventilation. Over the years, hospitals have gradually developed more sophisticated building designs, always finding ways to improve air quality. “It’s a science that is continually evolving,” Mr. McDavid said.


Hospitals now have elaborate filtration systems in place, including several banks of filters in various locations. When air is taken in from the outside, it typically passes through a prefilter, which cleans the air before it hits any equipment in the hospital’s heating, ventilation and air conditioning (HVAC) system. The air then travels through a return fan, then the heating and cooling components, another set of pre-filters, and the final filters—which, in the OR, are often high-efficiency particulate air (HEPA) filters. These are not the one- or two-inch HEPA filters the average person can buy, Mr. McDavid said. “These things are three feet deep.”

Air ducts are cleaned regularly, according to Mr. McDavid, an instructor for the National Air Duct Cleaners Association’s Certified Ventilation Inspector certification training course. The NADCA’s Assessment, Cleaning and Restoration standard recommends annual inspections of air-handling units, supply and return/exhaust ducts in health care facilities.

If a contagious patient must undergo a surgical procedure, it takes place in an airborne infection isolation room, which uses negative pressure to exhaust all air to the outside, passing through HEPA filters along the way, Amber Wood, RN, the senior perioperative practice specialist with the Association of periOperative Registered Nurses, said.


Negative pressure can increase the risk for surgical site infection, so facilities often operate in a positive pressure OR and adopt additional protective measures, such as limiting staff (all of whom must wear higher level respirators, or N95 masks), using a portable HEPA filter or ultraviolet germicidal irradiation to clean the OR air and waiting for a 99% exchange of new air before using the space for other patients, Ms. Wood said.

The bottom line is a bad HVAC system is bad for COVID-19. Earlier this year, researchers showed how one asymptomatic person likely infected nine others after all of them ate at the same restaurant, perhaps via strong airflow from the air conditioner, which spread virus-laden air between three tables (Emerg Infect Dis 2020 Jul. doi: 10.3201/eid2607.200764).

The virus is present in stool, so any traces in toilets can become aerosolized from a flush, Lidia Morawska, PhD, the director of the International Laboratory for Air Quality and Health at the Queensland University of Technology, in Brisbane, Australia, said. Indeed, a study of two hospitals in Wuhan, China, found elevated levels of SARS-CoV-2 RNA in aerosols taken from patients’ toilet areas (Nature 2020. doi: 10.1038/s41586-020-2271-3).


Because much about the airborne spread of the new virus remains unknown, some experts are looking to another virus for clues: SARS-CoV-1, which caused outbreaks of severe acute respiratory syndrome in the early 2000s. Researchers have documented numerous cases when the virus may have spread through the air, including in hospitals (Indoor Air 2004;15:83-95). One outbreak occurred after a patient with diarrhea visited a Hong Kong housing complex and used the toilet; soon after, more than 300 residents were infected (J Epidemiol Community Health 2003;57:652-654).

Given the concerns about potentially high airborne levels in bathrooms, Dr. Morawska recommended that hospitals increase ventilation in infected patients’ bathrooms, and maintain regular cleaning of bathroom surfaces.

Fortunately, the SARS-CoV-2 virus is not measles, Mr. McDavid said; most of the respiratory droplets that contain the new virus are likely large enough that they fall to the ground or other surfaces relatively quickly. In that scenario, protecting staff and patients in hospitals is mostly a matter of adequate protective gear and housekeeping, he said, using proper chemicals to wipe down surfaces.


“Yes, the new coronavirus is something different, and we’re learning a lot about it,” Mr. McDavid said. “But, really, the same mitigation efforts are in place as for mold, asbestos and other types of mitigation that have taken place over the years.”