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Aerosol emission from the respiratory tract: an analysis of aerosol generation from oxygen delivery systems
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  • Published on:
    Response to Priyadarshi
    • Fergus Hamilton, SpR Infection University of Bristol
    • Other Contributors:
      • AERATOR group, group

    We thank Nimmo et al for their comments on our paper, and for recognising that this work
    addresses an important gap in high quality data on aerosol generation and also the technical
    challenges associated with measuring aerosol from the respiratory tract.
    We agree that interparticipant variability in aerosol emission is significant (spanning several orders
    of magnitude) and acknowledge in the paper that interpretation of the data on patients with COVID-
    19 is limited due to the small cohort size. The AERATOR study was the first group to collect detailed
    aerosol measures from patients with active SARS-CoV-2, the aim of this exploratory sub group
    analysis was to consider if active infection had a meaningful impact on the use of healthy controls as
    proxies in the main analysis.
    Measuring aerosol emission from patients with COVID-19 is very challenging in the acute clinical
    setting because of both the very low aerosol background concentration required to make a
    measurement and infection control precautions. We therefore chose to report the raw data while
    acknowledging the difficulties in interpretation.
    In this analysis, we did not perform a sample size calculation; as we were limited by both
    epidemiological (level of COVID-19 infection in the community) and practical challenges, detailed
    Future studies could consider the collection of detailed aerosol measures from patients a...

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    Conflict of Interest:
    None declared.
  • Published on:
    • Radhika Priyadarshi, Senior Clinical Fellow , Respiratory Medicine Homerton University Hospital NHS Trust
    • Other Contributors:
      • Angshu Bhowmik, Consultant in Respiratory and General Medicine ,Lead Cancer Clinician | Co-Chair, Medical Advisory Group
      • Camus Nimmo, Speciality Trainee Registrar , Respiratory Medicine
      • Cassim Akhoon, Internal Medicine Trainee - 2
      • Santino Capocci, Consultant , Tuberculosis and Respiratory Medicine
      • Raj K Rajakulasingam, Consultant,Consultant Physician in Respiratory Medicine and Allergy and Honorary Clinical Professor in Medical Education

    The AERATOR study (Hamilton et al) compares and quantifies the risk of aerosol generation in both healthy patients and those infected with COVID-19 in a variety of contexts, including normal respiration, speaking and coughing, and the same activities whilst receiving therapy with continuous positive airway pressure (CPAP) and high-flow nasal oxygen (HFNO), and also whilst wearing a fluid-resistant surgical mask (FSRM)1. This study is particularly welcome as it is an area where data are scarce, yet the theoretical risks have major implications for both patients and health care professionals and influence recommendations that guide patient care, such as the use of side rooms and personal protective equipment, both of which are limited resources2. However, we have some questions about the study design.

    Hamilton et al demonstrated that the size of aerosols generated by healthy individuals and those infected with COVID-19 were comparable, thereby validating the use of healthy volunteers for aerosol characterisation, though the sample sizes involved within the COVID-19 cohort were relatively small (n=6). Furthermore, the study highlights that aerosolisation was lower in healthy volunteers with non-humidified CPAP, whilst it was increased in those receiving HFNO (though it was shown to originate mostly from the device), compared to baseline for breathing, speaking, and coughing. Given the study also mentions a considerable degree of inter- and intra-individual variability...

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    Conflict of Interest:
    None declared.