I have been reading both students’ final-year-project reports and a report commissioned by the NHS. I don’t know whether to be happy or sad that some of our students can write better reports than an august panel that includes a number of members of Royal Colleges. On the one hand it is great to see our students doing so well, but on the other hand at any one time the NHS is treating millions of patients, and you would hope that infection control in NHS hospitals would have rather more competent oversight.
I can’t of course share student reports with you, but as I coordinate the relevant module I looked up a very good report (that I hadn’t marked – they are marked by team of 20 academics). Please accept my word that it’s conclusion was a lot clearer than that of the report. I will go through the conclusion paragraph by paragraph, so brace yourself from some not-great use of English.
Overall, for these medical procedures of concern, the available evidence is not currently robust enough to demonstrate that these procedures generate significantly more aerosols than other types of care, or that exposure to the aerosols results in infection. Evidence derived from experimentally induced aerosols are not readily equated to human or clinical conditions and there was a lack of evidence to demonstrate a consistent risk of transmission that equates to procedures classified as high risk AGPs. Given the limited range and poor quality of the evidence, with many studies underpowered or vulnerable to bias and confounding, it is not possible to distinguish the absence of risk from the absence of evidence.
Independent report: Independent High Risk AGP Panel Summary of recommendations arising from evidence reviews to date, 9th June 2022
This is not too bad, although parsing the last sentence is not easy. I think they mean there is an absence of evidence so we can’t tell what the risk is. But the first sentence is correct, the available evidence for risk associated with the set of medical procedures called Aerosol Generating Procedures (AGPs) is indeed not ‘robust’.
In considering the mitigation of transmission of SARS-CoV-2 associated with the aerosols that may be generated when procedures cause coughing, sneezing or heavy breathing it is important to take account of the broader context of evidence. A combination of droplets and aerosols are emitted during breathing and talking. The concentration of particles increases during coughing and the increase is associated with much larger particles containing more fluid and potentially more virus. However, these particles are likely to remain airborne for less time. For transmission to occur, expelled respiratory secretions containing sufficient viable virus must be transferred to the mucous membranes of a susceptible individual either directly or via contaminated surfaces. The probability of this occurring is increased by proximity and duration of contact, and decreased by physical barriers that protect mucous membranes (for example, face masks, eye protection) and environmental factors that dilute the load of pathogen (for example, ventilation).
Independent report: Independent High Risk AGP Panel Summary of recommendations arising from evidence reviews to date, 9th June 2022
Here we are starting to hit problems, in the second sentence we have “combination of droplets and aerosols”. The Merriam-Webster dictionary defines aerosol as: “a suspension of fine solid or liquid particles in gas”. As liquid particles are droplets, then it is unclear what the difference between droplets in air and an aerosol. Rest of the paragraph is OK.
In hospitals, the application of administrative and engineering controls enables most patients with COVID-19 to be identified and segregated by prior testing and symptom screening and timing of procedures prioritised relative to the individual patient’s risk of being infectious. The hierarchy of controls should feature in all procedural planning in healthcare settings.
Independent report: Independent High Risk AGP Panel Summary of recommendations arising from evidence reviews to date, 9th June 2022
Fair enough, but how is this relevant? The final paragraph is:
Coughing is a major symptom in patients with COVID-19 and the use of droplet precautions (Type IIR fluid repellent surgical masks and eye protection) when caring for a patient who is coughing, or sneezing is considered effective for preventing transmission to healthcare workers. Therefore, for a medical procedure to require a higher level of protection it would need to be associated with an increase in aerosol production beyond that which would occur during the routine care of any COVID-19 patient. Approximately 20% of people with SARS-CoV-2 are likely to be asymptomatic. Although these people are able to transmit infection, the viral load, and relative risk of transmission is probably lower, although there remains uncertainty and more studies are required to quantify the risk precisely. The routine use of droplet precautions for close contact with all patients where the level of virus circulating in the community is high, mitigates the risk of transmission when delivering care to patients who have COVID-19 but are asymptomatic.
Independent report: Independent High Risk AGP Panel Summary of recommendations arising from evidence reviews to date, 9th June 2022
Which goes for “is considered effective for preventing transmission to healthcare workers”. Considered is doing a lot of heavy lifting in that sentence. Considered by whom? I have read some very good literature reports in my time at Surrey and in their conclusions they do what you should do. End with a key conclusion backed up by evidence, something like: “X is true as A, B and C have all shown via method Y which is appropriate because Z”. “Considered” is not a good substitute for “as A, B and C have all shown via method Y which is appropriate because Z”.
Others can speculate as to why this NHS report is so poor, I don’t know what went on behind closed doors. None of the 13 on the panel were aerosol scientists, which I am sure didn’t help. And medics have a rather unique, and very mechanical, style of reviewing the literature (see report here), which may work when combining a bunch of similar randomised controlled trial (RCTs) for a drug, but not for the much more diverse literature on aerosols in medicine. There is probably a systemic problem here with modern medicine, and how medical doctors are trained, which the pandemic has exposed.
Chance & Necessity 