Air filtration significantly reduces the presence of airborne SARS-CoV-2 in COVID-19 wards of hospitals, according to a study. Researchers at the University of Cambridge in the UK placed an air filtration machine in COVID-19 wards, and found that it removed almost all traces of airborne SARS-CoV-2.
The finding opens up the possibility of setting standards for cleaner air to reduce the risk of airborne transmission of infections, they said. The researchers noted that there has been a steady rise in the evidence that the SARS-CoV-2 virus can be transmitted through the air in small droplets called aerosols.
However, as hospitals have seen their capacity overwhelmed, they have been forced to manage many of their COVID-19 patients in repurposed 'surge' wards, which often lack the ability to change the air with a high frequency, they said.
The study, published in the journal Clinical Infectious Diseases, investigated whether portable air filtration and ultraviolet (UV) sterilisation devices could reduce airborne SARS-CoV-2 in general wards that had been repurposed as a COVID ward and a COVID Intensive Care Unit (ICU).
"Reducing airborne transmission of the coronavirus is extremely important for the safety of both patients and staff, said Vilas Navapurkar, from Cambridge University Hospitals (CUH), who led the study. "Effective PPE has made a huge difference, but anything we can do to reduce the risk further is important," Navapurkar said.
The team performed their study in two repurposed COVID-19 units. One area was a surge ward managing patients who required simple oxygen treatment or no respiratory support, and the second was a surge ICU managing patients who required ventilation.
The team installed a High Efficiency Particulate Air (HEPA) air filter/UV steriliser, which are made up of thousands of fibres knitted together to form a material that filters out particles above a certain size. The machines were placed in fixed positions and operated continuously for seven days, filtering the full volume of air in each room between five and ten times per hour.
In the surge ward, during the first week prior to the air filter being activated, the researchers were able to detect SARS-CoV-2 on all sampling days. Once the air filter was switched on and run continuously, the team was unable to detect SARS-CoV-2 on any of the five testing days.
They then switched off the machine and repeated the sampling. Once again, they were able to detect SARS-CoV-2 on three of the five sampling days. The team found limited evidence of airborne SARS-CoV-2 in the weeks when the machine was switched off and traces of the virus on one sampling day when the machine was active.
The air filters significantly reduced levels of bacterial, fungal and other viral bioaerosols on the both the surge ward and the ICU, highlighting an added benefit of the system, the researchers said. "We were really surprised by quite how effective air filters were at removing airborne SARS-CoV-2 on the wards," said study first author Andrew Conway Morris, from the University of Cambridge.
"Although it was only a small study, it highlights their potential to improve the safety of wards, particularly in areas not designed for managing highly infectious diseases such as COVID-19," Conway said. The research team developed a robust technique for assessing the quality of air, involving placing air samplers at various points in the room and then testing the samples using PCR assays similar to those used in the 'gold standard' COVID-19 tests.
"Cleaner air will reduce the risk of airborne disease transmission, but it's unlikely to be the case that just installing an air filter will be enough to guarantee the air is clean enough," Professor Stephen Baker, from the University of Cambridge, added.
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