Airborne transmission of covid-19
BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m3206 (Published 20 August 2020) Cite this as: BMJ 2020;370:m3206Read our latest coverage of the coronavirus outbreak
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Dear Editor
Thank you for analyzing and sharing the physics and physiology of the possibility of airborne transmission of Covid-19 infection in humans. I agree with the explained possible mechanisms of respiratory transmission of Covid-19 infection. There is always a chance of transmitting air through breathing while dealing with face-to-face contact with fellow human beings. I would like to recommend that everybody especially doctors, nurses, health professionals and front line workers take a front-to-side position that helps to decrease face-to-face (180-degree) airborne transmission of infectious agents/pollutants whenever and wherever possible.
Furthermore, proper use of appropriate masks, visor/face shield and physical distancing enhance 180-degree protection of the face against respiratory transmission of pollutants including Covid-19.
Competing interests: No competing interests
Dear Editor,
We would like to congratulate Dr. Fluxman on supporting the Editorial relating to aerosol spread of COVID. We raised this recently (https://www.bmj.com/content/370/bmj.m3249/rapid-responses) and it is highlighted in another article today (https://science.sciencemag.org/content/sci/369/6508/1146.full.pdf).
The research and computer simulations clearly show blasts of virus are carried in the air over distances of many metres. We have been arguing from the beginning of the pandemic, that common sense should inform us, COVID an essentially respiratory condition mainly acquired through inhalation of a virus, is transmitted by aerosols. It is therefore very disconcerting that WHO and other agencies have repeatedly asked for more scientific evidence, when as Dr Fluxman has indicated, this is already available for the closely related SARS! Ironically, the scientific evidence presented by WHO, PHE and SAGE to support their policies, is quite often inconsequential, indirect and not overwhelming.
It is highly unlikely we would have a pandemic on this scale purely by direct person to person spread. In the week, schools and many office workers return to work, some secondary schools are choosing to keep children in the classrooms during lunch breaks to stop the spread of virus, but the classrooms lack adequate ventilation! In many modern buildings of course there is no option to open windows, which raises another problem.
Competing interests: No competing interests
Dear Editor,
This paper by Wilson et al is to be warmly welcomed. At long last the issue of indoor airborne spread of Covid-19 is gaining traction within the medical profession, and the BMJ is to be congratulated on including it as an editorial, in keeping with the importance of this issue. It is to be hoped that this will spur PHE and the government to update what is plainly now inadequate and discredited offical guidance on transmission of Covid-19.
For many months aerosol scientists all over the world have been saying that current models of SARS-CoV-2 transmission do not withstand scrutiny. WHO, CDC and PHE guidance on transmission remains stuck, with a head in the sand response to the emerging evidence of the importance of aerosol spread, and an increasingly desperate rearguard defence of fomite and large droplet only spread and the discredited notion that aerosols are only generated by "aerosol generating procedures" within hospital. Wilson, one of the authors of this editorial, contributed to a paper in Anaesthesia in May https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7264768/, which decribed how aerosols are generated, and found that coughing dyspnoeic patients will release far more aerosols than someone being intubated. Vocalisation and effort of breathing dramatically increase aerosol production, neither of which occur in many so called AGPs. Unless a patient coughs during intubation almost no aerosols will be released; this study found only nebulised medication administration on its own and with bronchoscopy resulted in aerosols being produced. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6248660/
There also seems to be a requirement for a higher threshold for evidence of aerosol spread than for fomite and droplet spread of Covid-19. There is no gold standard, direct evidence for either of the officially recognosed routes for Covid-19, yet we accept these as being likely and adopt the precautionary principle in dealing with these risks of transmission. Yet for aerosol spread much more is required. There is now a considerable body of evidence for aerosol spread, indeed it seems more than for fomite or droplet spread, from basic aerosol physics to the finding of viable virus in the air up to 4.8m from an infected patients. The latter evidence was called for by WHO in their response to the scientists who wrote to them in early July. Will WHO now accept the reality of aerosol spread?
The situation here in the UK is all the more perplexing. For over 4 months documents from the government's own scientific advisory bodies have been saying that aerosol spread does occur, it is a significant risk and clear advice about mitigation measures against it are needed. On 14 April the Environmental Monitoring Group (which reports to SAGE) stated aerosols are produced by breathing and coughing and ventilation is required to reduce risk https://assets.publishing.service.gov.uk/government/uploads/system/uploa.... On 28 April EMG spoke again of airborne spread and the need for ventilation https://assets.publishing.service.gov.uk/government/uploads/system/uploa.... On 12 May the EMG raised the risk of aerosol transmission in hospital corridors. https://www.gov.uk/government/publications/possible-additional-intervent.... On 4 June the EMG discussed the risks of aerosol spread especially when people share poorly ventilated spaces. https://assets.publishing.service.gov.uk/government/uploads/system/uploa.... On 24 June the SAGE committee listed the three ways Covid-19 is transmitted: person to person; contact spread and by aerosols. https://assets.publishing.service.gov.uk/government/uploads/system/uploa....
How is it then that official guidance has not been updated to include this? There have been scores of outbreaks of Covid-19 in workplaces and other indoor environments, with workers being blamed for not observing social distancing or hygiene measures, when analysis of these events points clearly to typical superspreader events due to airborne transmission.
The public, employers, regulatory authroritiesand health professionals all need to be clearly informed about the dangers of ariborne spread and how to mitigate against it, in clearly set out official guidance. This clearly poses great challenges for everyone, as potentially any indoor space may be a risk for aerosol transmission. The current head in the sand approach does not make the evidence go away, and it perpetuates our hamstrung approach to tackling the pandemic, and can only lead to further increases in transmission across the country. One has to ask, why will the government not acknowledge and act on airborne spread of Covid-19?
Competing interests: No competing interests
Dear Editor, this is an important contribution to the debate on transmission of coronavirus and has pressing implications with the return to work and school and increasing numbers of outbreaks of Covid-19 in factories. There was always a fundamental contradiction in the World Health Organisation statement that simultaneously discounted airborne transmission - “According to current evidence, COVID-19 virus is primarily transmitted between people through respiratory droplets and contact routes. In an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported” - while at the same time declaring certain ‘aerosol generating procedures’ presented a particular risk for infection (1).
Currently the UK Food Standards Authority is investigating approximately 40 food processing plants but admits to having little hard data on the overall scale of the problem (2). This is despite the fact that the prime minister assured MPs in June the government was taking the prevalence of outbreaks in meat processing plants seriously. If guidance on containing spread of virus is in fact being implemented in food processing establishments as claimed, recent outbreaks of infection clearly point to the ineffectiveness of current advice and could provide potentially important lessons for infection control. The detailed investigation of an outbreak in a German meat processing plant for example (3), provided compelling evidence that climate conditions and airflow promoted efficient spread of SARS-CoV-2 over distances of more than 8m. Rather than indicating community acquired infection, this was a major super-spreader event within the workplace.
If infection in meat packing plants can be attributed to cramped working conditions, background noise (which leads to shouting), and poor ventilation, a similar situation prevails in other crowded, noisy, indoor environments, such as pubs, live music venues, gyms and schools. Ventilation therefore appears to be a critical risk factor that is amenable to modification (4). As Wilson and colleagues rightly state: “Accepting the importance of airborne transmission may prove a crucial breakthrough and should not be delayed further”.
References
1. https://www.who.int/news-room/commentaries/detail/modes-of-transmission-...
2. https://www.theguardian.com/world/2020/aug/27/covid-hundreds-self-isolat...
3. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3654517
4. https://theconversation.com/how-to-use-ventilation-and-air-filtration-to...
Competing interests: I am co-chair of 'Keep Our NHS Public', and a member of Doctors in Unite
Re: Airborne transmission of covid-19
Dear Editor
Given the poor correlation of "viral load" as measured on a pharyngeal swab with infectivity ( https://jamanetwork.com/journals/jamapediatrics/fullarticle/2768952 ), and that aerosolised virus is now recognised as being a potent driver of infections, then we need to look beyond the pharynx to figure out the source of aerosolisation.
Given knowledge of superspreading events in "phonation-loud" settings such as choirs, meatpacking plants, noisy pubs & bars, then this raises suspicion that the larynx is somehow involved.
Given that young children appear to be almost a dead-end host for SARS-CoV-2, yet will often demonstrate high "viral loads" on pharyngeal swabs ( https://jamanetwork.com/journals/jamapediatrics/fullarticle/2768952 ) then perhaps infectivity is tied to the number of viral receptors in the LOWER respiratory tract. There are far fewer ACE2 receptors in the lower respiratory tract of children compared to adults ( https://www.sciencedirect.com/science/article/pii/S2329050120301005 ). A lack of ACE2 receptors will also reconcile with the scarcity of lung disease in young children.
So what might tie this together more precisely is a posit that "aerosolisation of virus is in fact a process which occurs from larynx to lungs (i.e. it occurs within the lower respiratory tract, not the upper respiratory tract)".
In fact, this posit, when taken with another posit that "the infectious dose of virus is organ-specific and correlates inversely with the density of viral receptors", will go a long way towards explaining important epidemiological aspects of Covid-19 disease.
Competing interests: No competing interests