Oct. 11, 2021 -- A combination of HEPA filters and UV light was effective in reducing airborne COVID particles from the air of hospitals in the first test of its kind, researchers reported. 

The journal Nature reported this week that the research, which has not yet been peer-reviewed, suggests the filters may help reduce the risk of hospital-acquired SARS-CoV-2 -- the first such evidence in a real-world test. 

Researchers, led by intensivist Andrew Conway-Morris, PhD, with the Division of Anaesthesia in the School of Clinical Medicine at University of Cambridge, United Kingdom, write that earlier experiments assessed air filters' ability to remove inactive particles in carefully controlled environments, but it was unknown how they would work in a real-world setting.

Co-author Vilas Navapurkar, MBChB, an ICU physician at Addenbrooke's Hospital in Cambridge, U.K., said that hospitals have used portable air filters when their isolation facilities are full, but evidence was needed as to whether such filters are effective or whether they provide a false sense of security.

The researchers installed the filters in two fully occupied COVID-19 wards — a general ward and an ICU. They chose HEPA filters because they can catch extremely small particles.

The team collected air samples from the wards during a week when the air filters were on and 2 weeks when they were turned off, then compared results.

According to the study, "airborne SARS-CoV-2 was detected in the ward on all five days before activation of air/UV filtration, but on none of the five days when the air/UV filter was operational; SARS-CoV-2 was again detected on four out of five days when the filter was off."

Airborne SARS-CoV-2 was not frequently detected in the ICU, even when the filters were off.

Cheap and Easy

According to the Nature article, the authors suggest several potential explanations for this, "including slower viral replication at later stages of the disease." Therefore, the authors say, filtering the virus from the air might be more important in general wards than in ICUs.

The filters significantly reduced the other microbial bioaerosols in both the ward (48 pathogens detected before filtration, 2 after) and the ICU (45 pathogens detected before filtration, 5 after).

National Institute for Occupational Safety and Health (NIOSH) cyclonic aerosol samplers and PCR tests were used to detect airborne SARS-CoV-2 and other microbial bioaerosol.

David Fisman, MD, an epidemiologist at the University of Toronto, Canada, who was not involved in the research, said in the Nature article, "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."