Viable virus aerosol propagation by positive airway pressure circuit leak and mitigation with a ventilated patient hood
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Abstract
Nosocomial transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a major feature of the COVID-19 pandemic. Evidence suggests patients can auto-emit aerosols containing viable viruses; these aerosols could be further propagated when patients undergo certain treatments, including continuous positive airway pressure (PAP) therapy. Our aim was to assess 1) the degree of viable virus propagated from PAP circuit mask leak and 2) the efficacy of a ventilated plastic canopy to mitigate virus propagation.
Methods
Bacteriophage phiX174 (10 8 copies·mL −1 ) was nebulised into a custom PAP circuit. Mask leak was systematically varied at the mask interface. Plates containing Escherichia coli host quantified viable virus ( via plaque forming unit) settling on surfaces around the room. The efficacy of a low-cost ventilated headboard created from a tarpaulin hood and a high-efficiency particulate air (HEPA) filter was tested.
Results
Mask leak was associated with virus contamination in a dose-dependent manner (χ 2 =58.24, df=4, p<0.001). Moderate mask leak (≥21 L·min −1 ) was associated with virus counts equivalent to using PAP with a vented mask. The highest frequency of viruses was detected on surfaces <1 m away; however, viable viruses were recorded up to 3.86 m from the source. A plastic hood with HEPA filtration significantly reduced viable viruses on all plates. HEPA exchange rates ≥170 m 3 ·h −1 eradicated all evidence of virus contamination.
Conclusions
Mask leak from PAP may be a major source of environmental contamination and nosocomial spread of infectious respiratory diseases. Subclinical mask leak levels should be treated as an infectious risk. Low-cost patient hoods with HEPA filtration are an effective countermeasure.
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SciScore for 10.1101/2020.09.04.20187922: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:This study, however, has several limitations. First, we used a nebuliser which produces a tight range of particle size (3.42µm ± 0.15µm) to produce virus containing aerosols. In contrast, aerosols generated by individuals when …
SciScore for 10.1101/2020.09.04.20187922: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:This study, however, has several limitations. First, we used a nebuliser which produces a tight range of particle size (3.42µm ± 0.15µm) to produce virus containing aerosols. In contrast, aerosols generated by individuals when they speak or breathe are of similar magnitude (30) but present a much larger range of particle sizes including larger droplet ranges. Larger droplets settle faster and are less likely to travel long distances. Second, because of our detection sensitivity, we aerosolised larger numbers of viruses than has been shown to be emitted as aerosol by infected individuals when breathing (109 vs 105 (9)). However, these levels are well balanced by other factors, such as the degree of surface area sampled within the room and shorter periods of time measured. Further discussion related to the number of viable viruses settling for each given leak is provided in the supplementary materials (Table S3). Importantly, nebulizing 109 phages directly up into the room most likely represents a ‘worse case’ clinical scenario. This showcases the extremely high efficacy of the hood and HEPA filtration structure to mitigate infection risk. In summary, our results demonstrate that untended mask leak from PAP therapy can be a source of environmental contamination which can be mitigated by the use of a hood and HEPA filter. The hood and portable HEPA filter may represent a relatively low cost and portable adjunct to HCW protection from nosocomial COVID-19 transmission.
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
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