Hunziker, P.

Oct 12, 2021
BMJ Open

Objective 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. Result 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. Conclusion 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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