From the Journals

HEPA filters may clean SARS-CoV-2 from the air: Study


High-efficiency particulate air (HEPA) filters and ultraviolet (UV) light sterilization effectively remove SARS-CoV-2 particles from the air — the first such evidence in a real-world test, researchers report in the preprint server medRxiv.

The journal Nature reported Oct. 6 that the research, which has not been peer-reviewed, suggests the filters may help reduce the risk of hospital-acquired SARS-CoV-2.

Researchers, led by intensivist Andrew Conway-Morris, MBChB, 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, United Kingdom, 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, P = .05) and the ICU (45 pathogens detected before filtration, 5 after P = .05).

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, 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.”This work was supported by a Wellcome senior research fellowship to co-author Stephen Baker. Conway Morris is supported by a Clinician Scientist Fellowship from the Medical Research Council. Dr. Navapurkar is the founder, director, and shareholder of Cambridge Infection Diagnostics Ltd. Dr. Conway-Morris and several co-authors are members of the Scientific Advisory Board of Cambridge Infection Diagnostics Ltd. Co-author Theodore Gouliouris has received a research grant from Shionogi and co-author R. Andres Floto has received research grants and/or consultancy payments from GSK, AstraZeneca, Chiesi, Shionogi, Insmed, and Thirty Technology.

A version of this article first appeared on

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