Research at a hospital swamped by people with COVID-19 has confirmed that portable air filters effectively remove SARS-CoV-2 particles from the air — the first such evidence in a real-world setting1. The results suggest that air filters could be used to reduce the risk of patients and medical staff contracting SARS-CoV-2 in hospitals, the study’s authors say.
Despite the proper use of personal protective equipment, hospitals have reported substantial spread of SARS-CoV-2 from patients to health-care workers. One suspected cause of such cases is viral particles in the air, which are one of the main drivers of SARS-CoV-2 transmission.
Earlier experiments that tested air filters’ performance assessed their ability to remove inactive particles while operating in carefully controlled environments2. As a result, “what was not known was how effective they would be in a real-world ward setting for clearing SARS-CoV-2”, says study co-author Vilas Navapurkar, an intensive-care unit (ICU) physician at Addenbrooke’s Hospital in Cambridge, UK. Hospitals have turned to portable air filters as an attractive solution when their isolation facilities are full, Navapurkar says, but it’s important to know whether such filters are effective or whether they simply provide a false sense of security.
To determine how the filters stand up to real-world conditions, Navapurkar and his co-authors installed them in two fully occupied COVID-19 wards — a general ward and an ICU. The team chose high-efficiency particulate air (HEPA) filters, which blow air through a fine mesh that catches extremely small particles. The researchers collected air samples from the wards during a week when the air filters were switched on and two weeks when they were turned off.
In the general ward, the team found SARS-CoV-2 particles in the air when the filter was off but not when it was on. Surprisingly, the team didn’t find many viral particles in the air of the ICU ward, even when the filter there was off. The authors suggest several possible reasons for this, including slower viral replication at later stages of the disease3. As a result, the team says that measures to remove the virus from the air might be more important in general wards than in ICUs.
A simple solution
“This study suggests that HEPA air cleaners, which remain little-used in Canadian hospitals, are a cheap and easy way to reduce risk from airborne pathogens,” says David Fisman, an epidemiologist at the University of Toronto, Canada, who was not involved in the research.
And the scientists found that the filters don’t only protect against SARS-CoV-2. When the filters were switched off, the air in both wards contained detectable amounts of other pathogens that cause infections in hospitals, such as Staphylococcus aureus, Escherichia coli and Streptococcus pyogenes. The filters largely removed them. These organisms are not typically thought to spread through the air, but “this study suggests that these infections may also spread by aerosol”, Fisman says.
The findings have not yet been peer reviewed.
Conway-Morris, A. et al. Preprint at medRxiv https://doi.org/10.1101/2021.09.16.21263684 (2021).
Mousavi, E. S., Kananizadeh, N., Martinello, R. A. & Sherman, J. D. Environ. Sci. Technol. 55, 4134–4147 (2021).
Wölfel, R. et al. Nature 581, 465–469 (2020).