This is the first study to report that both TNE and LGI endoscopy are aerosol and droplet generating. We are also the first to report on defined particle generating events and associated particle sizes within procedures performed via the mouth, nose and rectum. Both POG and TNE should therefore be classed as AGPs, whilst the classification of LGI endoscopy depends on the definition of AGP used. For UGI endoscopy, in some countries the use of patient facemasks is becoming widespread though there have been few studies quantifying their impact on aerosol and droplet generation²³. A randomised study recently found that a mouthpiece did not reduce smaller size particles (<1.0μm), which in the context of our findings may suggest limited reduction of risk²⁴: further studies in this area are certainly warranted. However, our aim here is to establish what can be expected during standard endoscopy, without the use of facemasks, that is still the usual practice in most endoscopy units worldwide.

With regards to POG, our results confirm those of previous studies showing this is an AGP, producing particles at double the background level. The most significant contributing event is local anaesthetic throat spray application, which generates ten times the number of particles compared to a volitional cough, with an average particle size in the aerosol range. By comparison, a recent study showed that controlled endotracheal intubation and extubation in asymptomatic patients generate only a fraction of the aerosols generated by volitional coughing.²⁵ The particles recorded with throat spray application are potentially infectious, as they would have rebounded from the patient’s oropharynx or occasionally, been contributed by coughing induced by the throat spray. There is additional risk because the throat spray is applied face-on with the patient. It is therefore important that barrier methods such as face shields or goggles are used whilst applying throat and nasal spray.

Extubation is the second most particle generating event in POG and is also significantly more particle generating than volitional cough. However, a higher proportion of particles is in the droplet range (and reaches up to 3000μm), which has a lower risk for airborne transmission. This is understandable as both insufflation in the oesophagus and the movement of the wet shaft of the endoscope on extubation will generate particles.⁸ Coughing/gagging are also significant generators of particles, and is predictably comparable to the level of particles produced by volitional coughing, although we did not find that the use of sedation reduced particle counts over the whole procedure. The usefulness of suctioning, described by Chan et al,¹⁵ cannot be commented on in our study, as intermittent suctioning was applied in all of our cases.

Interestingly, during volitional coughing, we found the presence of a hiatus hernia gives increased levels of particles, with an average size in the aerosol range. This may be due to the loss of the physiological lower oesophageal sphincter, which would enable aerosols to be expelled unimpeded from the stomach and out of the mouth as abdominal muscles are contracted during coughing. Previous studies have found negligible impact of sedation on aerosol production, in agreement with our findings, but have found significant positive correlation with BMI which we did not observe^15,16. We expect that this is because of increased inter-patient variation in our study caused by looser confinement of aerosols – for example, one previous study placed the patient’s head in an enclosure. However, we purposefully designed our study with looser constraints to enable direct comparison between UGI and LGI (for which building a suitable enclosure would be challenging) and to replicate realistic procedure conditions so as to measure aerosol exposure likely to be experience by healthcare workers.

TNE has been suggested by some as a non-AGP method for performing UGI endoscopy, although the generation of aerosols from intranasal application of spray has already been suggested.^26-27 Our results show that TNE is an AGP and produces particles predominantly in the aerosol range, which may also have implications for similar otolaryngology procedures. Nasal spray application, nasal intubation and nasal extubation were all associated with significant spikes of particles. TNE generates approximately half the level of particles than POG; therefore, if used with additional mitigating strategies (avoidance of nasal spray, barrier methods) TNE could potentially become a non-AGP procedure.

With regards to LGI endoscopy, our study shows the absolute levels of particles produced are greater than UGI procedures, but are about one third lower when taken per unit time. Although there would be a greater exposure to aerosols in LGI procedures due to longer procedures, these are therefore more likely to be cleared in well ventilated rooms. We recognise that COVID-19 is primarily a respiratory pathogen, and feco-oral transmission has not been proved. The risk from LGI procedures is likely to be considerably lower than equivalent aerosols generated by UGI procedures. However, it should be noted that infection of intestinal cells and viral replication has been shown,²⁷ and SARS-Cov-2 RNA has been detected in stools,²⁸ whilst there are also implications for other types of gastrointestinal pathogens. There have been attempts to mitigate aerosol and droplet diffusion during colonoscopy using specially designed shorts with a diaphragm to pass the colonoscope.²⁹

An important source of interference to consider for LGI endoscopy occurs during patient position changes. We observe that turning a patient in the bed before the procedure has even started results in a large spike in measured particles, which is probably due to air movement and the rubbing of materials. The clinical relevance of position changes is therefore difficult to interpret but we are able to identify, isolate and exclude these from analysis where appropriate.

In this study, we have characterised aerosol and droplet generation from the different routes of GI endoscopy. We emphasise, however, that aerosols may not necessarily contain viable virus material and so their generation does not equate to infectivity of the procedures themselves. This depends on multiple factors, including which part of the patient the particles are being generated from; particles from the oral and nasal cavities are likely to have a much higher potential infectivity risk compared to those from the large bowel. As the infectivity of procedures is not established, we therefore suggest adequate PPE (including high-efficiency masks) and sanitization of floors and surfaces (to prevent resuspension of aerosols) is used for all GI endoscopy where there is a high population prevalence of COVID-19.