key: cord-0900618-ctralhne authors: DUFFY, C.; KIDD, A.; FRANCIS, S.; TSIM, S.; MCNAUGHTON, L.; FERGUSON, K.; FERGUSON, J.; RODGERS, G.; McGROARTY, C.; SAYER, R.; BLYTH, K. G. title: CHEST DRAIN AEROSOL GENERATION IN COVID-19 AND EMISSION REDUCTION USING A SIMPLE ANTI-VIRAL FILTER date: 2020-07-15 journal: nan DOI: 10.1101/2020.07.13.20152264 sha: 90df84337ab17dc71f0efe92a455577237405e39 doc_id: 900618 cord_uid: ctralhne INTRODUCTION The COVID-19 pandemic has been characterised by significant in-hospital virus transmission and deaths among healthcare workers. Sources of in-hospital transmission are not fully understood, with special precautions currently reserved for procedures previously shown to generate aerosols (particles <5 microns). Pleural procedures are not currently considered AGPs, reflecting a lack of data in this area. METHODS An underwater seal chest drain bottle (R54500, Rocket Medical UK) was set up inside a 60-litre plastic box and connected via an airtight conduit to a medical air supply. A multichannel particle counter (TSI Aerotrak 9310 Aerosol Monitor) was placed inside the box, allowing measurement of particle count/cubic foot (pc/ft3) within six channel sizes: 0.3-0.5, 0.5-1, 1-3, 3-5, 5-10 and >10 microns. Stabilised particle counts at 1, 3 and 5 L/min were compared by Wilcoxon signed rank test; p-values were Bonferroni-adjusted. Measurements were repeated with a simple anti-viral filter, designed using repurposed materials by the study team, attached to the drain bottle. The pressure within the bottle was measured to assess any effect of the filter on bottle function. RESULTS Aerosol emissions increased with increased air flow, with the largest increase observed in smaller particles (0.3-3 microns). Concentration of the smallest particles (0.3-0.5 microns) increased from background levels by 700, 1400 and 2500 pc/ft3 at 1, 3 and 5 L/min, respectively. However, dispersion of particles of all sizes was effectively prevented by use of the viral filter at all flow rates. Use of the filter was associated with a maximum pressure rise of 0.3 cm H2O after 24 hours of flow at 5 L/min, suggesting minimal impact on drain function. CONCLUSIONS A bubbling chest drain is a source of aerosolised particles, but emission can be prevented using a simple anti-viral filter. These data should be considered when designing measures to reduce in-hospital spread of SARS-CoV-2. Previous coronavirus epidemics were characterised by high infection rates in healthcare workers (HCWs) and 'super-spreading' events within hospitals. Despite implementation of World Health Organisation (WHO) guidance designed to reduce in-hospital spread, [1] nosocomial and HCW infection have remained prominent features of the current COVID-19 pandemic, with 43.5% of UK HCWs becoming seropositive over a 1-month period in one recent study. [2] Better understanding of in-hospital infection sources is therefore urgently needed. Pleural procedures are not currently considered aerosol-generating by the WHO [1] , and special precautions to mitigate against viral transmission and/or to protect HCWs are not currently recommended. However, this is based on the absence of any prior data regarding the aerosol generating potential of a chest drain (where an aerosol is defined as a particle smaller than 5 microns) rather than a robust understanding of the level of risk involved. Recent studies report detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in COVID-19-associated pleural effusion [3, 4] and 'super-spreading' events linked to chest drain use. The latter includes a cohort of 25 Chinese patients (including 12 HCWs) infected from a single index case who underwent elective lobectomy with undetected SARS-CoV-2 infection. [5] This has prompted expert bodies, including the British Thoracic Society (BTS) [6] and the American Association for the Surgery of Trauma (AAST) [7] to recommend risk mitigation of some form until the level of risk involved is more clearly understood. The objectives of this study were to determine a) whether a bubbling chest drain is aerosol generating and b) the efficacy of a simple anti-viral filter. The experimental set-up used is shown in Figure 1 . An underwater seal chest drain bottle (R54500, Rocket Medical UK, Ltd) was set up according to the manufacturer's instructions and placed inside a sealable 60-litre plastic box. The drain tubing (Ref R54502) was attached to a medical air cylinder via an airtight conduit in the wall of the box. A multichannel particle counter (TSI Aerotrak 9310 Aerosol Monitor) was placed inside the box, allowing measurement of particle count/cubic foot (pc/ft 3 ) within six channel sizes: 0.3-0.5, 0.5-1, 1-3, 3-5, 5-10 and >10 microns. Stabilised particle counts at different flow rates (without and with the filter attached) were compared by Wilcoxon signed rank test (R version 4.0.2 (Vienna, Austria)); p-values were adjusted for multiple comparisons by the Bonferroni method. For . CC-BY-NC-ND 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) The copyright holder for this preprint this version posted July 15, 2020. . https://doi.org/10.1101/2020.07.13.20152264 doi: medRxiv preprint filter comparisons, relative differences, normalised to without-filter readings, were assessed. Ethical approval was not required. A COVID-19 anti-viral filter device was designed by the study team and manufactured using repurposed equipment (see Figure 1 , and online supplement for detailed Instructions for Particle concentrations in the air surrounding the chest drain were initially sampled without the filter attached. Baseline conditions were first sampled for 20 minutes. Medical air was then pumped through the circuit for 20 minutes at 1 L/minute, before being switched off, allowing baseline conditions to re-stabilise over a further 20 minutes. After each 60-minute experiment the box was opened, measurements were recorded, and the unit resealed. The experiment was repeated using flow rates of 3 and 5 L/minute, and then all three experiments were repeated with the filter attached (see Figure 1 (b)). is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted July 15, 2020. The data reported here indicate that particles in the aerosol range (<5 microns) are generated by a bubbling chest drain at continuous flow rates of at least 1 L/minute. Aerosol emissions increased with increasing air flow, simulating a high-volume air-leak, as might be expected following thoracic surgery, in mechanically ventilated patients or patients with a large spontaneous alveolar-pleural fistula complicating bullous lung disease. These data were recorded as part of a comprehensive risk assessment process, which demonstrated no significant limitation of air flow through the chest drain circuit with the filter in-situ. Aerosols are typically generated by air moving across the surface of a liquid, with increasing air forces generating smaller particles. [1] This is consistent with the observations reported here in that unfiltered emissions of the smallest particles (0.3-0.5 microns) increased progressively from 1 to 3 to 5 L/minute. Our findings are also concordant with a recent study reported by Akhtar et al, in which a similar anti-viral filter was evaluated and produced a qualitative reduction in droplet emissions. However, droplet size, and therefore aerosolization potential were not examined. [8] These data support risk mitigation in patients with suspected or proven COVID-19, as recommended by the British Thoracic Society (BTS) [6] and the American Association for the Surgery of Trauma (AAST). [7] However, the absolute risk involved remains uncertain. Pleural effusion and pneumothorax appear uncommon complications of COVID-19 (occurring in ~5% and ~1% of cases, respectively [6] [8]) and an . CC-BY-NC-ND 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 preprint this version posted July 15, 2020. . https://doi.org/10.1101/2020.07.13.20152264 doi: medRxiv preprint aerosol-generating chest drain can clearly only be an infection risk if SARS-CoV-2 is a) present in any effusion drained (which may be of minimal volume in patients with pneumothorax and major air-leaks) and b) remains viable long enough to be aerosolised. Lescure [3] and Mei [4] have recently reported cases of SARS-CoV-2 positive effusions, but in these cases air-leak was not reported as a significant component, and larger studies are needed to define the prevalence and risks of unfiltered air-leaks in COVID19 more clearly. In a recent post-mortem series, Schaller et al reported that 50% of patients with fatal COVID-19 had associated pleural effusion, of which 50% were PCR positive. The experiments reported here were carried out in a controlled environment with minimal background environmental disturbances. It is therefore unknown how normal background activities (e.g. staff proximity, the opening and closing of doors), which can affect the rate of aerosols resuspension on surfaces, would affect concentrations in a clinical setting. Given that our data were recorded at flow rates of 1, 3 and 5 L/minute it should also be acknowledged that the particle emission profile of smaller volume air-leaks cannot be directly concluded from our data. Nevertheless, it appears clear that a bubbling chest drain is a source of aerosolised particles, and that dispersion can be prevented using a simple anti-viral filter. These data should be considered when designing measures to reduce in-hospital spread of SARS-CoV-2. . CC-BY-NC-ND 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 preprint this version posted July 15, 2020. . https://doi.org/10.1101/2020.07.13.20152264 doi: medRxiv preprint ACKNOWLEDEMENTS CD had full access to all of the data in the study, contributed substantially to the study design, data analysis and interpretation, and wrote a first draft of part of the manuscript AK contributed substantially to the study design, and interpretation, and wrote a first draft of part of the manuscript SF and RS had full access to all of the data in the study, contributed substantially to the study design, data analysis and interpretation, and the writing of the manuscript ST, KF, JF, LM, GR, CM contributed substantially to the study design, data analysis and interpretation, and the writing of the manuscript KGB conceived the study, had access to the data and takes responsibility for the integrity and the accuracy of the data analysis, had the primary role in writing and submitting the manuscript and acts as guarantor. KGB has received research funding from Rocket Medical UK Ltd for other studies. All other authors have no competing interests to declare. . CC-BY-NC-ND 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 preprint this version posted July 15, 2020. . CC-BY-NC-ND 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 preprint this version posted July 15, 2020. . CC-BY-NC-ND 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 preprint this version posted July 15, 2020. . https://doi.org/10.1101/2020.07.13.20152264 doi: medRxiv preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted July 15, 2020. . https://doi.org/10.1101/2020.07.13.20152264 doi: medRxiv preprint . CC-BY-NC-ND 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 preprint this version posted July 15, 2020. . https://doi.org/10.1101/2020.07.13.20152264 doi: medRxiv preprint 3c . CC-BY-NC-ND 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. 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