key: cord-0721862-la3e7hzl
authors: Simonds, Anita K.
title: ‘Led by the science’, evidence gaps, and the risks of aerosol transmission of SARS-COV-2
date: 2020-05-15
journal: Resuscitation
DOI: 10.1016/j.resuscitation.2020.05.019
sha: 61a02b350d32108632b640ba50dfa63f83cdec3a
doc_id: 721862
cord_uid: la3e7hzl

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greater mass are assumed to travel less than 2 meters from source, and land in the vicinity of the patient. Infection control measures are therefore designed to minimise spread by direct or indirect contact, dissemination by droplets, and transmission by airborne material. Some medical interventions are more likely to generate aerosol. These are interesting results, adding to argument that chest wall compression may be an AGP but it raises further questions. It is clear that a plume of material was produced from both models, but particle size was not measured. It is likely than some aerosol generated was that from nebuliser in the simulator model. The presence of viral antigen within these droplets, and the infectivity of the material are further important variables. The exposure 'dose' from a cough, sneeze or exhalation is likely to vary according to the proximity of the healthcare worker (HCW) to the patient's airway, the patient's viral load, and the use and type of PPE protection. It is also plausible that underlying conditions such as asthma, bronchiectasis, and COPD may not only increase propensity to cough or wheeze, but may produce secretions with different muco-elastic properties, which affect particle size and behaviour. A study 8 of droplet dispersion during a physiotherapy session designed to clear airway secretions in a group of patients with purulent sputum due mainly cystic fibrosis and bronchiectasis, produced droplets of 10 microns and above, and no detectable aerosol.

Sputum produced in this group is observably different to clearer more mucoid secretions in those with viral infection and no pre-existing airway disease.

In a study of cough aerosol production in healthy normal subjects without infection, this work does suggest that influenza, at any rate, can be spread by the airborne route, rather than by droplets and contact alone. The same research group has also examined the efficacy of face shields against cough aerosol and droplets generated by a cough simulator 11 . They found that face shields can very significantly protect from short term 9

It is of concern that infection of health and social care workers in the covid-19 pandemic has been significant. This has generally not occurred in areas such as Critical Care units where use of enhanced PPE is near universal as most patients are intubated and receiving a range of AGPs. These new considerations on aerosol generation are relevant to those examining and assessing patients in Accident and Emergency or ENT departments, and the care workers in the community, where PPE for droplet and direct contact infection control may not suffice, and suboptimal protection may contribute to increased infection risk. This concern is over and above the reported lack of supply of adequate PPE to staff.

We should be led by the science and evidence base, but this should be updated and revised according to new analyses, and frontline experience with SARS-COV-2. While infection control guidance based on AGP/airborne versus droplet precautions is a useful and pragmatic concept leading directly to PPE choices, risk management in real life is likely to be more complicated involving host factors in the patient, the technical procedures employed, and clinical context.

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