Using air filtration to remove airborne SARS-CoV-2 and other microbial aerosols in COVID wards

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RNA from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been detected in air samples from coronavirus disease (COVID-19) departments, illustrating airborne spread of the virus.

The UK turned several general wards into specialized intensive care units (ICUs) during the COVID-19 pandemic when hospitals faced a shortage of beds. However, these rooms did not have the capacity to perform frequent air changes.

Although healthcare workers use appropriate personal protective equipment (PPE) capable of filtering out medium and large droplets, viral transmission from patients to hospital staff is common, attributed to inhaling viral particles in small aerosols (

Studies have shown that improved ventilation combined with ultraviolet (UV) light sterilization is a better preventive measure than respiratory protective equipment. It has been proposed that portable air filtration systems, capable of combining high efficiency particle filtration and UV light sterilization, may be a feasible solution to ward off respiratory SARS-CoV-2.

Setting

Researchers at the University of Cambridge conducted a study in two reassigned COVID-19 units at Addenbrooke’s Hospital, Cambridge, UK, between January and February 2021. During this period, the alpha variant (lineage B1.1.7) accounted for> 80% of circulating SARS. -CoV-2. This study, published on medRxiv* preprint server, aimed at providing proof of removal of SARS-CoV-2 and microbial bioaerosols using portable air filters with UV sterilization.

The study was conducted in a converted “emergency room” and “emergency intensive care unit”. The emergency department took care of patients requiring simple oxygen therapy or no respiratory assistance, and no aerosol-generating procedures were performed. An AC1500 HEPA14 / UV sterilizer has been installed in this department.

Patients in the emergency intensive care unit were managed with invasive and non-invasive respiratory support with non-invasive mask ventilation, high-flow nasal oxygen or invasive ventilation Going through endotracheal tube or tracheostomy. A Medi 10 HEPA13 / UV sterilizer has been installed in this department.

The air filters were attached before the start of the three-week study. During the second week, the air filters were turned on and operated continuously for 24 hours a day, providing approximately 5-10 filtrations per hour in the room volume.

The study involved a cross-assessment with the primary aim of detecting SARS-CoV-2 in various size fractions of air samples from emergency room and surge ICU with and without filtration of the air, with UV sterilization.

To detect the presence of airborne SARS-CoV-2 and other microbial bioaerosols, two-stage cyclonic aerosol samplers and multiplex qPCR assays from the National Institute for Occupational Safety and Health (NIOSH) were used.

The Mann-Whitney U test was used to compare the difference in the number of pathogens detected when the air filter was on and off – statistical significance being inferred when p values ​​were 0.05.

Location of air filters and room layout.  A) Arrangement of the room in the “surge” service with four beds.  B) Layout on the “surge” intensive care unit with six beds, including the addition of the extra bed to increase occupancy (labeled with rad box).  NIOSH air sampler locations indicated by *.  The air filters were installed at the marked locations and set to operate at 1000 m3 / hour.  The volumes of the rooms are respectively about 107 m3 and 195m3.  Fresh air was not supplied or extracted in these areas.

Location of air filters and room layout. A) Arrangement of the room in the “surge” service with four beds. B) Layout on the “surge” intensive care unit with six beds, including the addition of the extra bed to increase occupancy (labeled with rad box). NIOSH air sampler locations indicated by *. The air filters were installed at the marked locations and set to operate at 1000 m3 / hour. The volumes of the rooms are respectively about 107 m3 and 195m3. Fresh air was not supplied or extracted in these areas.

Air filter efficiency in service

During the first week, when the air filter was not active, SARS-CoV-2 could be detected over the five sampling days in the medium and large particle fractions (> 4 M in size of particles), but not on small (

During the second week, when the air filter was on and running continuously, SARS-CoV-2 RNA was not detected in any of the sample fractions. Sampling was then repeated with an inactive air filter. SARS-CoV-2 RNA was detected in medium and large particulate fractions during three out of five days of sampling, as well as multiple viral, bacterial and fungal pathogens.

On the other hand, when the air filter was operational, only the yeast was detected. In addition, microbial bioaerosols have decreased significantly.

Intensive care air filter efficiency

Meanwhile, the ICU obtained limited evidence of airborne SARS-CoV-2 in weeks one and three (filter disabled), but detected SARS-CoV-2 RNA in a single sample in the fraction average particulate during the second week (filter activated). The use of the air filtration device significantly (p = 0.05) reduced microbial bioaerosols, even in the intensive care unit.

Discussion

Recent data from studies indicate that exertional respiratory activity, like that in COVID-19 patients, increases the release of respiratory aerosols by 1 to 4 M. conventional, such as high-flow nasal oxygen and non-invasive ventilation, reduce aerosol generation during exercise. This study agrees with these data, postulating that precautions may be more important in the wards.

The low burden of SARS-CoV-2 in intensive care may be due to multiple factors – a higher level of aerosolized PPE used, patients being in advanced stages of the disease – where viral replication is less pronounced, higher viral loads in the lower part rather than the upper respiratory tract in critically ill patients; and the use of a respirator which reduces aerosol generation.

In the intensive care unit, the reduction in microbial bioaerosols with a functioning air filtration system indicates that the device was just as effective.

Although several building codes offer air filtration to reduce the transmission of airborne diseases, these have not been updated to take COVID-19 into account.

This presents the first report describing the successful elimination of airborne SARS-CoV-2 in hospital settings using combined air filtration and UV sterilization technology.

Observations confirm that air filtration devices can help reduce the risk of nosocomial SARS-CoV-2.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.

Journal reference:

  • Removal of airborne SARS-CoV-2 and other microbial bioaerosols by air filtration on COVID-19 surge units Andrew Conway Morris, Katherine Sharrocks, Rachel Bousfield, Leanne Kermack, Mailis Maes , Ellen Higginson, Sally Forrest, Joannna Pereira-Dias, Claire Cormie, Timothy Old, Sophie Brooks, Islam Hamed, Alicia Koenig, Andrew Turner, Paul White, R. Andres Floto, Gordon Dougan, Effrossyni Gkrania-Klotsas, Theodore Gouliouris, Stephen Baker, Vilas Navapurkar, medRxiv, 2021.09.16.21263684; do I: https://doi.org/10.1101/2021.09.16.21263684, https://www.medrxiv.org/content/10.1101/2021.09.16.21263684v1


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