Minimising exposure to respiratory droplets, ‘jet riders’ and aerosols in air-conditioned hospital rooms by a ‘Shield-and-Sink’ strategy
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Abstract
In COVID-19, transfer of respiratory materials transmits disease and drives the pandemic but the interplay of droplet and aerosol physics, physiology and environment is not fully understood. To advance understanding of disease transmission mechanisms and to find novel exposure minimisation strategies, we studied cough-driven material transport modes and the efficacy of control strategies.
Design
Computer simulations and real-world experiments were used for integrating an intensive care setting, multiphysics and physiology. Patient-focused airflow management and air purification strategies were examined computationally and validated by submicron particle exhalation imaging in volunteers.
Setting
Hospital setting during a respiratory virus pandemic with transmission by respiratory droplets and aerosols.
Participants
Healthy volunteers.
Outcome measures
Distribution of, and exposure to, potentially infectious respiratory secretions.
Results
Respiratory materials ejected by cough exhibited four transport modes: long-distance ballistic, short-distance ballistic, ‘jet rider’ and aerosol modes. Interaction with air conditioning driven flow contaminated a hospital room rapidly. Different than large droplets or aerosols, jet rider droplets travelled with the turbulent air jet initially, but fell out at a distance, were not well eliminated by air conditioning and exposed bystanders at larger distance and longer time; their size predisposes them to preferential capture in the nasal mucosa, the primordial COVID-19 infection site. ‘Cough shields’ captured large droplets but induced lateral dispersion of aerosols and jet riders. An air purification device alone had limited efficacy. A ‘ Shield and Sink’ approach combining cough shields with ‘virus sinks’ minimised exposure to all secretions in modelling and real-life experiments.
Conclusions
Jet riders have characteristics of highly efficient respiratory infection vectors and may play a role in COVID-19 transmission. Exposure to all droplet types can be minimised through an easily implemented Shield and Sink strategy.
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SciScore for 10.1101/2020.12.08.20233056: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement Consent: The persons visualized in figures and supplements gave written informed consent for participation and consented to their images and videos being published for scientific purposes. 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:Increasing air flow rate from rates on one side led …
SciScore for 10.1101/2020.12.08.20233056: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement Consent: The persons visualized in figures and supplements gave written informed consent for participation and consented to their images and videos being published for scientific purposes. 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:Increasing air flow rate from rates on one side led to more aerosols leaving the room per time interval, but on the other side induced more turbulent room air flow at the given geometry, favoring air mixing and thus potentially transporting aerosol-loaded air from non-breathing zones towards breathing zones; therefore, the benefit of just increasing ventilation thus has limitations that depend on the specific characteristics of a room and A/C system. Cough shields: Cough “shields” were partly effective in stopping forward-directed cough droplets but led to a redirection of the air stream carrying aerosols, including in the direction of adjacent beds and nurse workplaces at the side of the patient bed, an effect which is not desired. Also, air flow around obstacles is a well-known physical phenomenon36 that limits the effectiveness of such shields for aerosol plumes. Air filtering: Air purification by filtering with a high flow, HEPA filter equipped commercially available air filtering device, was examined. We found in modeling as well as in real-world experiments (E-cigarette smoke distribution) that such an air filtering device alone, even when positioned near the patient head, only has a limited capabililty for directly and quantitatively removing droplets/aerosols from the cough jet because the jet velocities away from the device were sufficiently high to overcome the modest pressure/velocity gradient produced by the device. Non patient centered air filtering has been show...
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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