key: cord-311486-auuyjct6
authors: Cook, T. M.
title: Personal protective equipment during the COVID‐19 pandemic: a reply
date: 2020-06-04
journal: Anaesthesia
DOI: 10.1111/anae.15158
sha: 
doc_id: 311486
cord_uid: auuyjct6

nan

I thank Professor Murphy for his interest [1] in my article [2] . There is a great danger that an anaesthetist steps well 'outside their lane' when discussing respiratory particle physics and fluid dynamics. These are complex sciences in their own right, in which I have no training.

That said, I think we largely agree that respiratory secretions vary in size over several magnitudes and this will affect their behaviour when expelled from the respiratory tract. For clarity, I neither stated that particles above 5 µm were large nor referred at all to whether these are visible or not and I am unclear why these are referred to in Professor Murphy's letter.

Particles of around 5 µm diameter are especially important because this is the (perhaps historical) cut-off used by most sources for defining behaviour as a droplet (>5 µm) or an aerosol (<5 µm) and because particles of these size are of the appropriate size to reach the alveoli rather than depositing higher up in the respiratory tract [2] .

However, the behaviour of particles is highly complex, not dependent only on size and much debated: as I stated in my article "the dichotomy into> 5 and < 5 µm particles leading to droplet or airborne spread, respectively, is likely to be simplistic, with aerosols being maintained over a wider range of particle size". I infer that Professor Murphy's concerns are that larger particles than described contribute to aerosols and therefore that airborne transmission is a significant risk, and that the 2 m 'droplet zone' is insufficient. 

Royal United Hospitals Bath NHS Foundation Trust, Bath, UK Email: timcook007@gmail.com No external funding or competing interests declared.

Personal protective equipment during the coronavirus disease (COVID) 2019 pandemic -a narrative review

Personal protective equipment during the coronavirus disease (COVID) 2019 pandemic -a narrative review

The role of particle size in aerosolised pathogen transmission: a review

Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations

Centers for Disease Control and Prevention. Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease

corona virus-infection-prevention-and-control/transmission-characte ristics-and-principles-of-infection-prevention-and-control