key: cord-0300922-qfrenkb6
authors: Conway Morris, A.; Sharrocks, K.; Bousfield, R.; Kermack, L.; Maes, M.; Higginson, E.; Forrest, S.; Pereira-Dias, J.; Cormie, C.; Old, T.; Brooks, S.; Hamed, I.; Koenig, A.; Turner, A.; White, P.; Floto, R. A.; Dougan, G.; Gkrania-Klotsas, E.; Gouliouris, T.; Baker, S.; Navapurkar, V.
title: The removal of airborne SARS-CoV-2 and other microbial bioaerosols by air filtration on COVID-19 surge units
date: 2021-09-22
journal: nan
DOI: 10.1101/2021.09.16.21263684
sha: 5030555cf1b5c09913bd5dadcfd4ebc59dc6bae4
doc_id: 300922
cord_uid: qfrenkb6

Background The COVID-19 pandemic has overwhelmed the respiratory isolation capacity in hospitals; many wards lacking high-frequency air changes have been repurposed for managing patients infected with SARS-CoV-2 requiring either standard or intensive care. Hospital-acquired COVID-19 is a recognised problem amongst both patients and staff, with growing evidence for the relevance of airborne transmission. This study examined the effect of air filtration and ultra-violet (UV) light sterilisation on detectable airborne SARS-CoV-2 and other microbial bioaerosols. Methods We conducted a crossover study of portable air filtration and sterilisation devices in a repurposed surge COVID ward and surge ICU. National Institute for Occupational Safety and Health (NIOSH) cyclonic aerosol samplers and PCR assays were used to detect the presence of airborne SARS-CoV-2 and other microbial bioaerosol with and without air/UV filtration. Results 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 infrequently detected in the ICU. Filtration significantly reduced the burden of other microbial bioaerosols in both the ward (48 pathogens detected before filtration, two after, p=0.05) and the ICU (45 pathogens detected before filtration, five after p=0.05). Conclusions These data demonstrate the feasibility of removing SARS-CoV-2 from the air of repurposed surge wards and suggest that air filtration devices may help reduce the risk of hospital-acquired SARS-CoV-2.

The study was registered as a service evaluation with Cambridge University Hospitals NHS Foundation Trust (Service Evaluation Number PRN 9798).

. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted September 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 5 Summary

The COVID-19 pandemic has overwhelmed the respiratory isolation capacity in hospitals; many wards lacking high-frequency air changes have been repurposed for managing patients infected with SARS-CoV-2 requiring either standard or intensive care. Hospital-acquired COVID-19 is a recognised problem amongst both patients and staff, with growing evidence for the relevance of airborne transmission. This study examined the effect of air filtration and ultra-violet (UV) light sterilisation on detectable airborne SARS-CoV-2 and other microbial bioaerosols.

We conducted a crossover study of portable air filtration and sterilisation devices in a repurposed 'surge' COVID ward and 'surge' ICU. National Institute for Occupational Safety and Health (NIOSH) cyclonic aerosol samplers and PCR assays were used to detect the presence of airborne SARS-CoV-2 and other microbial bioaerosol with and without air/UV filtration.

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 infrequently detected in the ICU. Filtration significantly reduced the burden of other microbial bioaerosols in both the ward (48 pathogens detected before filtration, two after, p=0.05) and the ICU (45 pathogens detected before filtration, five after p=0.05).

These data demonstrate the feasibility of removing SARS-CoV-2 from the air of repurposed 'surge' wards and suggest that air filtration devices may help reduce the risk of hospital-acquired SARS-CoV-2.

Wellcome Trust, MRC, NIHR . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted September 22, 2021.

During the COVID-19 pandemic 'general' hospital wards in the UK were rapidly repurposed into 2 'surge' wards and intensive care units (ICU), which lacked the capacity for high frequency air-3 changes. Airborne dissemination is likely an important transmission route for SARS-CoV-2 1 , with 4 SARS-CoV-2 RNA being detected in air samples from wards managing COVID-19 patients 2,3 .

Despite the use of appropriate personal protective equipment (PPE) that filter medium and large size 6 droplets, there are multiple reports of patient-to-healthcare worker transmission of SARS-CoV-2 4,5,6, 7 potentially through the inhalation of viral particles in small (< 5µM) aerosols 7 . Furthermore, 8 nosocomial acquisition of COVID-19 has continued to blight healthcare systems despite the 9 systematic introduction of patient and healthcare worker asymptomatic screening programmes 8 . There 10 is a need to improve the safety for healthcare workers and patients during the pandemic by decreasing 11 the potential for the airborne transmission of SARS-CoV-2 7 . Engineering solutions that improve 12 ventilation with provision of UV light sterilisation are considered a more effective intervention in the 13 hierarchy of controls against transmissible infections compared to enhanced respiratory protective 14 equipment 9,10 . Portable air filtration systems, that combine high efficiency particulate filtration and 15 ultraviolet (UV) light sterilisation, may be a scalable solution for removing respirable SARS-CoV-2.

A recent review by the UK Scientific Advisory Group for Emergencies modelling group found 17 limited data regarding the effectiveness of such devices 11 , which is consistent with findings from two 18 recent systematic reviews 12, 13 . Most of the testing of such systems has been physical device 19 validation using inorganic particles or removal of bacterial bioaerosols in controlled test environments 20 12,13 . Here we present the first data providing evidence for the removal of SARS-CoV-2 and microbial 21 bioaerosols from the air using portable air filters with UV sterilisation on a COVID-19 'surge' ward 22 during the ongoing pandemic.

The study was conducted in two repurposed COVID-19 units in Addenbrooke's Hospital, Cambridge, 27 UK in January/February 2021 when the alpha variant (lineage B1.1.7) comprised >80% of circulating 28 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted September 22, 2021. ; https://doi.org/10.1101/2021.09.16.21263684 doi: medRxiv preprint 7 SARS-CoV-2 8 . One area was a 'surge ward' (ward) managing patients requiring simple oxygen 29 therapy or no respiratory support, the second was a 'surge ICU' (ICU) managing patients requiring 30 invasive and non-invasive respiratory support. The ward was a fully occupied four-bedded bay ( The samplers were operated on weekdays (0815hrs to 1415hrs) for three consecutive weeks. After 52 sampling, the samplers were disassembled using sterile technique and the filter papers were 53 transferred to 15 ml Falcon tubes. The samples were processed then stored at −80°C until analysis.

The samplers were washed with 80% ethanol and demineralised water.

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Removal of SARS-CoV-2 by air filtration on surge ward 72 For the duration of the study (18 th January to 5 th February) the beds in the ward and ICU were at 73 100% occupancy, with 15 patients admitted to the ward and 14 admitted to the ICU over the three-74 week sampling period (7, 4, 4 in weeks 1-3 in the ward and 6, 5, 3 in the ICU, respectively). All In the ward, during the first week whilst the air filter was inactive, we were able to detect SARS-CoV-82 2 on all five sampling days; RNA was detected in both the medium (1-4μM particle size) and the 83 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted September 22, 2021. ; 9 large (>4μM particle size) particulate fractions ( Fig. 2A) . SARS-CoV-2 RNA was not detected in the 84 small (<1μM) particulate filter. The air filter was switched on in week two and run continuously; we 85 were unable to detect SARS-CoV-2 RNA in any of the sampling fractions on any of the five testing 86 days. These initial observations provided evidence for the removal of SARS-CoV-2 via the air filter 87 system, albeit at high baseline C T values. To confirm this observation, we completed the study by 88 repeating the sampling with an inactive air filter. As in week one, we were able to detect SARS-CoV-89 2 RNA in the medium and the large particulate fractions on 3/5 days of sampling (a sample without 90 tube size indicated tested positive on day 5) (Fig. 2A) . We did not detect SARS-CoV-2 RNA from the 91 control sampler.

We subjected the extracted nucleic acid preparations to high-throughput qPCR using a Biomark HD 95 system to detect a range of viral, bacterial, and fungal targets. In the week one samples, we detected 96 nucleic acid from multiple viral, bacterial, and fungal pathogens on all sampling days (Fig. 2B) . In 97 contrast, when the air filter was switched on, we detected yeast targets only on a single day, with a 98 significant reduction (p=0.05) in microbial bioaerosols when the air filter was operational (Fig. 2C ).

Using this high-throughput approach, SARS-CoV-2 RNA was detected on 4/5 days tested in week 1 100 but was again absent in week 2. We were unable to generate multiplex data for week three due to 101 sample degradation after storage of sample following SARS-CoV-2 RNA amplification.

In contrast to the ward, we found limited evidence of airborne SARS-CoV-2 in weeks one and three 105 (filter off) but detected SARS-CoV-2 RNA in a single sample in the medium (1-4μM particle size) 106 particulates on week 2 (filter on) (Fig. 3A) . This contrary result did not reflect a general lack of 107 bioaerosols in the ICU, which demonstrated a comparable quantity and array of pathogen associated 108 nucleic acids to that seen in the unfiltered ward air on week one (Fig. 3B) . Again, the use of the air 109 filtration device significantly (p=0.05) reduced the microbial bioaerosols ( Fig 3C) ; with only three 110 . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted September 22, 2021. ;  12 This study has limitations, being conducted rapidly in active wards during an ongoing pandemic. The 166 evaluation was conducted in two rooms and there are no data defining the optimal air changes 167 required to remove detectable pathogens with the specified devices. Given the large volume of air 168 within the room and the stability of viruses in the sampling fluid, it was predictable that the amount of 169 SARS-CoV-2 detected via qPCR would be minimal, as evidenced by high C T values. Therefore, we 170 cannot categorically state that there was circulating infectious virus. RNA is sufficient to suggest the 171 virus was present and it has been shown that aerosolised virus can remain infectious for >3 hours 27,28 ; 172 additionally, air sampling devices can artefactually reduce the apparent viability of sampled virus. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted September 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 A) Layout of the room on the 'surge' ward with four beds. B) Layout on the 'surge' ICU with six beds including the addition of the additional bed to increase occupancy (labelled with rad box). Locations of the NIOSH air samplers indicated by *. The air filters were installed in the marked locations and set to operate at 1000 m 3 /hour. The rooms volumes are approximately 107 m 3 and 195m 3 respectively. Fresh air was not supplied or extracted in these areas.

. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint Figure 2 . Bioaerosol detection in specific air sampler fractions over the three-week testing period on the 'surge' ward.

A) C T values for SARS-CoV-2 qPCR on air sample fractions collected daily from the ward. Colours indicate the specific component of the sampler where SARS-CoV-2 was detected. Components collected aerosols dependent on size fractions; large >4 µm, medium1-4 µm, small <1 µm. B) Daily detection of fungal, bacterial and viral bioaerosols detected by high-throughput qPCR collected during weeks one (filter off) and two (filter on). The differences in C T values between the regular qPCR (A) and high-throughput qPCR (B) are a function of the microfluidics technology, and do not reflect higher bioaerosol burdens. C) Stacked bar chart showing collated total number of bioaerosol detections during weeks one (filter off) and two (filter on). *p=0.05 by Mann-Whitney U test.

. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint A) C T value for the single qPCR SARS-CoV-2 detection on day 9 (week 2) in the medium (1-4 µm particle size) fraction. B) Daily detection of fungal, bacterial and viral bioaerosol detected by high-throughput qPCR collected during weeks one (filter off) and two (filter on). The differences in C T values between the regular qPCR (A) and high-throughput qPCR (B) are a function of the microfluidics technology, and do not reflect higher bioaerosol burdens. C) Stacked bar chart showing collated total number of bioaerosol detections during weeks one (filter off) and two (filter on). *p=0.05 by Mann-Whitney U test.

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The copyright holder for this this version posted September 22, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 

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