They don’t even speak the same language

Parlons-nous la même langue à propos des gouttelettes ? Non, nos gouttelettes sont différentes

[Gouttelettes = Droplets]

Profile Picture of Evonne T CurranThe primary pandemic error is reflected in the quote “Understanding respiratory pathogen transmission is essential for public health measures aimed at reducing pathogen spread”. Gralton et al 2010.  This blog will show there was no shared understanding of respiratory pathogen transmission and thus precautions for healthcare workers (HCWs) were inadequate and unsafe. This was a failure of the organisations providing infection prevention and control (IPC) guidance in the UK. Whilst debate has centred around whether airborne transmission was the dominant mode, it went unnoticed that there were significant differences between organisations’ definitions of droplet transmission (the organisations’ stated mode of transmission of SARS-CoV-2). Several organisations, whose role involved HCW safety, used widely different definitions – without apparently realising there were differences – or that such differences would have health consequences for people. The significant difference is that from 2011, droplet transmission in the UK was reported to involve inhalation; yet the authors failed to recognise that to prevent inhalation of virus would require respiratory protection for HCWs.

 

The Health and Safety Executive  HSE document 2008, World Health Organization (WHO)  WHO 2014, Centres for Disease Control and Prevention CDC 2007 (CDC) all agreed that droplets were splashed/sprayed/touched onto the facial mucous membranes. The WHO 2014 additionally stated (without the support of citations) that droplets reached as low as the pharynx. However, the National Infection Prevention and Control Manuals [NIPCMs] (Scotland and England) relied on a Literature Review v3 October 2020 from NSS which had produced a definition that involved droplets descending down the respiratory tree to just above the alveoli. The Dept. of Health’s pandemic planning Routes of influenza transmission (DoH 2011) document, also used this definition with citations. However, collectively, and individually, they both failed to note the consequences of droplets descending to just above the alveoli; that is, as entry could only be by inhalation, respiratory protection was required.

 

The Routes of influenza transmission (DoH 2011) helpfully defined inhalable droplets as “Particles that enter the body through the nose and/or mouth during breathing which travel no further than the tracheobronchial tree”. They differentiated those inspirable droplets from respirable (aerosols) “as inhaled particles that penetrate to the alveolar region of the lung”. Thus, the Dept. of Health (2011) and NSS Literature Review v3 October 2020 definitions of ‘droplet transmission’ included signifiers of airborne transmission. Importantly, as they both note, for airborne infection, there is only one level of protection against airborne infections and that is respiratory protection equipment – RPE, e.g., filtering face piece (FFP masks).

 

National Services Scotland had received criticism for the quality of their monthly reviews of the literature regarding SARS-CoV-2 transmission from an independent report commissioned by the Royal College of Nursing (2021). Somewhat surprisingly the NSS monthly reviews never cited their own literature review’s definition of droplet transmission (nor anybody else’s).  In response to the criticism National Services Scotland released a statement which answered that they were “fully aligned with that of the World Health Organisation IPC guidance recommendations published to date”. This could only be interpreted as true if the NSS definition did not involve inhalation. However, because the NSS definition of ‘droplet transmission’ was fundamentally different to that of the WHO, they were in fact misaligned. The WHO described the risk from direct contact (via spray/splash/contact) – whilst NSS were describing inhalation.

 

What is significant about droplets (and their viral payload) descending to above the alveolar level is that the tracheobronchial tree is one of the many receptor sites for SARS-CoV-2. Of note, the Dept. of Health Routes of influenza transmission (DoH 2011)  said that influenza multiplies throughout the respiratory tract. Thus, unless the receptor cells are only to be found in the alveoli, it should be considered that all respiratory pathogens in inhalable droplets can gain access to receptor cells in the tracheobronchial tree. Simultaneously, the UK IPC via their national manual produced guidance advising HCWs that the only protection needed was against splash, whilst their literature review described droplets as being inhaled to the tracheobronchial tree, lined with SARS-CoV-2 ACE2 receptor cells. Clearly, a new way to differentiate when HCWs need respiratory protection (other than an unevidenced paradigm of droplets or aerosols) is urgently needed.

 

Another reason that all respiratory infections should be considered in some part airborne, and which is included in all definitions, is that droplets can shrink to become ‘droplet nuclei’. So, if everyone agrees with the physics that droplets shrink, and on shrinking the droplet nuclei behave like aerosols, (and are inhaled) then either the pathogen is only ever in aerosol sized particles from the start, or all respiratory transmission involves some degree of inhalation.  Indeed, the Dept. of Health Influenza strategy (2011) stated, “spread of the disease is also possible via fine particles and aerosols but the contribution to spread is as yet still unclear”.  Again, this is further evidence that the droplet or aerosol paradigm is not real. Additionally, if the Dept. of Health’s influenza strategy authors are unsure of the contribution of aerosols, they are patently unsure of the contribution of any mode of transmission.

 

So, as all respiratory transmission of pathogens appears to involve some degree of airborne transmission. The errors above are eliminated with the adoption of the new paradigm – which suggests the old droplet or airborne pathogen defies physics and all particles ≤100µm are inhaled. None of the definitions from any of the organisations charged with safety at work was entirely correct. The NSS and Dept. of Health were accurate in stating droplets were inhalable – but failed to see the safety consequences of this. I cannot find an updated HSE definition after the 2008 document which used a size dichotomy of <5µm and >5 µm (sic – particles sized 5 appear in no group).

 

Evaluating the Gralton et al 2010 quote from the start, they (organisations charged with HCW safety) did not understand respiratory pathogen transmission and thus failed in producing public health measures capable to optimally reduce nosocomial transmission.

 

In conclusion, the NSS literature reviews found evidence that supported droplets being inhaled to above the alveolar level, precisely where there was an abundance of receptor cells waiting for the virus. However, they failed to recognise the consequences of this phenomena as HCWs requiring RPE. The WHO, CDC and  HSE document failed to define droplet transmission as involving inhalation; Ergo, any stated alignment by NSS with the WHO’s IPC recommendations was in error and moot. The lack of citations by WHO should have caused alarm bells to ring.

 

Of note none of the organisations involved in HCW safety:

  • Determined whether other organisations’ droplet transmission definitions aligned with their own,
  • Considered the implications for IPC if there were differences,
  • Looked at whether other organisations’ evidence base provided sufficient evidence to support their definition,
  • Detected that as their definition involved inhalable droplets, the HCWs required RPE.

 

Clearly, reflecting on the title, the major IPC organisations do not speak the same language in relation to droplets….

 

Recommendations: All organisations involved in HCW safety should ensure their definitions are evidenced, aligned and do not defy physics. They should also ensure their recommended precautions befit the evidenced mode of transmission.

 

The airborne or droplet paradigm cannot be evidenced. It should be abandoned for a system which reflects the vulnerability of HCWs when exposed to infectious patients.

 

This all should have happened before the virus’ 5th birthday.

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