At the start of the pandemic it was thought that spread of coronavirus was through large droplets travelling over a relatively short distance or by fomites contaminating hands and mucous membranes. The danger of aerosol spread was recognised, but thought to be limited to ‘aerosol generating procedures’ (AGP) such as intubation. For this reason, high grade face masks (FFP3 or N95) were only recommended for staff exposed to AGP (1).
The denial of aerosol transmission of virus (2) always sat uncomfortably with the acceptance that so called AGP represented a risk. It is now known that aerosols are generated by talking, shouting, singing, coughing and sneezing and are an important form of viral transmission. Official Infection Prevention and Control (IPC) guidance [3] is now seriously lacking on the issue of AGPs: several studies [4] [5] [6] indicate that many of the “classic” AGPs (like intubation) produce little in the way of aerosols and that an actively coughing patient may be much more infectious than those undergoing various AGPs. Moreover, patients with Covid-19 requiring AGPs are likely to be sicker and later on in their illness course, and will therefore produce much less aerosolised virus than patients who have just become symptomatic, when infectiousness is known to be at its greatest.
In fact, coronavirus can be spread over large distances, for example in food processing plants (7) or in restaurant settings. Studies in health workers of SARS-CoV-2 antibody status (signifying past infection) (8) strongly suggest that high level PPE (including high grade masks) is effective in preventing infection, and that use of surgical type fluid resistant masks is inadequate in situations where staff are in close contact with symptomatic patients such as on hospital wards.
In addition, ventilation in enclosed and crowded workspaces is clearly an important risk factor in spread, yet there is little specific advice to manage this risk other than keeping windows open. This is a particular concern in workplaces and schools where maintaining social distancing is difficult; currently the highest rate of new infection is among secondary school children. The fact that a recent update of official IPC guidance does not mention aerosol spread at all (outside of AGPs) is inexplicable, given that this was after Public Health England recognised this route of transmission over two month ago. This puts tens of thousands of health and social care workers at potential risk in hospitals, primary care settings and in care homes, as well as the patients they care for.
The pandemic is far from over, with more than 600 health and care workers already having died, and an overall death toll in the UK equivalent to one international airplane crash killing all passengers every day for nine months. Although vaccine development gives some cause for hope, important unknowns remain how many people will receive/accept vaccination and how long this process will take, whether vaccination will prevent transmission and therefore achieve herd immunity, and how long protection might last. There is therefore every reason to hone non-pharmacological interventions in order to reduce further loss of life. We therefore call upon PHE and the Department of Health and Social Care to recognise an urgent need to update guidelines on COVID-19 prevention and control in the light of what is now known about aerosol transmission. This should include upgrading type of masks worn (9) and advice on how to maintain and monitor effective ventilation.
References
- https://www.gov.uk/government/publications/wuhan-novel-coronavirus-infection-prevention-and-control
- https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations
- https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/910885/COVID-19_Infection_prevention_and_control_guidance_FINAL_PDF_20082020.pdf
Doctors in Unite 