An Aerosol Generating Procedure (AGP) describes an activity that can result to the release of small airborne particles (aerosols) or droplets. Under certain conditions, the release might contain potentially transmissible quantities of virial material; the current focus of this document.
The mechanisms of aerosol release are associated with:
Low temperature (usually under 60°C) evaporation processes where virial material could survive and be suspended in air
Operations generally involving high shear stresses or/and rates on materials that could potentially be suspended in air
Aerodynamic interactions between materials/streams of materials that could generate or/and intensify or/and spread new or pre-existing aerosols/pre aerosolised material
AGPs with virus transmission potential are diverse and could include, apart from medically associated operations, common activities such as playing wind instruments1, singing2, sneezing, coughing, physically intensive activities that involve vigorous exhalation etc.
Public Health England (PHE) lists the following medical procedures for COVID-19 associated with increased risk of respiratory transmission3,4:
tracheal intubation and extubation
tracheotomy or tracheostomy procedures (insertion or removal)
dental procedures (using high speed devices, for example ultrasonic scalers/high speed drills)
Amount and variability of overall viable SARS-CoV-2 virons released from each AGP and associated transmissivity thread.
Types/measurement methods to adequately quantify/measure released material.
For dental operations and their subsequent use of high rotating speed pneumatic powered equipment (e.g. microturbine handset drills), a suggestion of using lower speed, high torque, electrically powered micromotor handsets seems to be reducing the amount of expelled material6,7.
Mitigation routes (including dynamic prediction of fallow times) per process.
There is a lack of high quality studies which have examined the risk of transmission of microbes responsible for acute respiratory infections to healthcare workers caring for patients undergoing AGP8.
Lack of precision in the definition for aerosol generating procedures8.
Amount of actual virial material in released emissions per droplet/particle especially when AGP involves secondary fluids (e.g. water for instrument cooling etc.)
Threshold of virial content volume in droplet to transmit the virus
Aerosol and droplet emission generation mechanisms at the microscale to allow specific mitigation processes as a result of altered/modified operation of action or/and design of instrumentation used.
Characteristics of expelled particles/droplets for each procedure including velocity and trajectory from source.
He, R., Gao, L., Trifonov, M. & Hong, J. Aerosol generation from different wind instruments. J. Aerosol Sci.151, 105669 (2021).
Bahl, P. et al. Droplets and Aerosols Generated by Singing and the Risk of Coronavirus Disease 2019 for Choirs. Clin. Infect. Dis. 2019–2021 (2020). doi:10.1093/cid/ciaa1241
Public Health England. COVID-19: Guidance for the remobilisation of services within health and care settings. Infection prevention and control recommendations. Infection prevention and control recommendations (2020).
Assessing the evidence base for medical procedures which may create a higher risk of respiratory infection transmission from patient to healthcare worker. (2020).
Jackson, T. et al. Classification of aerosol-generating procedures: a rapid systematic review. BMJ Open Respir. Res.7, e000730 (2020).
Implications of COVID-19 for the safe management of general dental practice A practical guide. 06-16 (2020).
Mitigation of Aerosol Generating Procedures in Dentistry. (2020).
Tran, K., Cimon, K., Severn, M., Pessoa-Silva, C. L. & Conly, J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: A systematic review. PLoS One7, (2012).
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