Independent report

Independent High Risk AGP Panel Summary of recommendations arising from evidence reviews to date

Updated 8 July 2021

Public Health England (PHE) provides independent secretariat to the Independent High Risk AGP Panel and is in no way involved in the decision-making process of the panel.

Main summary points

This advice relates to high risk Aerosol Generating Procedures (AGPs) and presents outputs from 3 deliverables from the Independent High Risk AGP Panel.

The first is a background briefing document detailing the context for decision-making related to risk of COVID-19. The second is an evidence review commissioned and funded by the National Institute for Health Research (NIHR), produced by the Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre, a facility for producing systematic reviews to inform policy). This evidence review considered medical procedures which do not meet the current WHO definition for high risk AGP. These are procedures which may induce coughing, heavy breathing or sneezing in the patient undergoing the procedure and have been highlighted to the panel as procedures of concern by professional organisations. The procedures included in the review were: nasogastric tube insertion, cardiopulmonary exercise and lung function tests, spirometry, swallowing assessment, nas(o)endoscopy and suction in the context of airway clearance (not associated with intubation or mechanical ventilation).

It concludes that 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.

The third is an international review of AGP lists in other countries. This indicates that the United Kingdom (UK) AGP list is comprehensive in comparison to other countries, and broader in its inclusions than the WHO and European Centre for Disease Prevention and Control (ECDC) lists. However, 2 procedures - nebulisation and cardiopulmonary resuscitation (CPR) - were common to 5 or more countries high risk AGP lists and are not on the UK list currently. Both have been previously considered by the UK Infection Prevention and Control (IPC) cell, which concluded that they do not currently have a strong evidence base linking them with increased risk of infection transmission. However, these may be considered high risk by some countries due to the likelihood of being performed with other high risk procedures such as intubation or manual ventilation. The UK high risk AGP list includes intubation and ventilation, so some of these differences are about how the procedures are classified and the language used to describe them.

The advice based on all of the above evidence is that none of the procedures included in the evidence review are proposed to be included in the extant UK AGP list.

Advice for future research needs are also detailed including the need for international guidelines for aerosol sampling and measurements for AGP studies that include characterisation of the entire range of particle sizes, which are rarely measured. Standardisation of data collection and calibration against recognised standards in clinical settings is also needed to allow for pooling of data for synthesis and meta-analysis. Clinical studies should be prioritised and coordination is required with regards to ensuring that different research groups, often from different medical and dental specialties, are aware of each other’s projects and to ensure that AGP research gaps are being addressed in a timely fashion with robust, shared methodology. There is a need for coordinated funding calls both nationally and internationally.

Introduction

Aerosol Generating Procedures (AGPs) are commonly presumed to be any medical or patient care procedure that results in the production of airborne particles (aerosols). However, the WHO recommends the application of enhanced precautions for ‘high risk AGPs’ which are defined as medical procedures that ‘have been reported to be aerosol-generating and consistently associated with an increased risk of pathogen transmission’ (World Health Organization, 2014).

This summary presents the outputs from 3 deliverables from the Independent High Risk AGP Panel. The first of these is a background document detailing the evidence, the second an evidence review of medical procedures which do not meet the current WHO definition for high risk AGP and the third the results of an international review which examined high risk AGP lists in other countries worldwide.

The evidence review of medical procedures which do not currently meet the WHO high risk AGP definition

The purpose of this evidence review was to inform recommendations for medical procedures which do not meet the WHO definition for high risk AGP to date, however, are subject to professional society and organisational concerns about their potential for generating infectious aerosols of SARS-CoV-2. These are procedures which may induce coughing, heavy breathing or sneezing in the patient undergoing the procedure. The procedures included in the review were: nasogastric tube insertion, cardiopulmonary exercise and lung function tests, spirometry, swallowing assessment, nas(o)endoscopy and suction in the context of airway clearance (not associated with intubation or mechanical ventilation). The review sought to evaluate evidence that these procedures generate infectious aerosols and are associated with a risk of transmission of respiratory infection, inclusive of SARS-CoV-2.

Findings of the review

There was limited evidence from 2 retrospective cohort studies of staff who were caring for patients with SARS-CoV and undertook a range of AGP and non-AGP procedures, including nasogastric tube insertion. There was no evidence of an association between nasogastric tube insertion and the acquisition of SARS-CoV infection.

There was 1 simulation study that investigated droplet/aerosol production in healthy volunteers undergoing pulmonary lung function tests. Tidal volumes, functional residual capacity and forced expiratory volume test were associated with low or very low production of aerosols and coughing was associated with a significant increase in particles. There were limitations in the methods used to detect particles and the study did not provide evidence for emission of respiratory viruses.

There were 9 studies that examined aerosol/droplet generation associated with endoscopic sinus surgery (nasoendoscopy), of which 7 were cadaveric or porcine models and 2 clinical observations. A further 4 studies (1 clinical observation; 3 simulation - cadaver or human volunteers) on outpatient nasoendoscopy. The findings in relation to aerosol generation were not consistent and most studies did not use robust measures or account for potential confounders, the simulation studies did not account for patient factors such as coughing and nasal secretions and no studies involved respiratory viruses. Clinical observation studies provided some evidence for a significant increase in airborne particle concentrations associated with the use of powered instruments such as microdebriders and drills, and during procedures involving nasoendoscopy with debridement.

There were 6 studies which examined aerosol generation in relation to the use of suctioning. However, these predominantly focused on the use of suction in the context of AGPs, or did not provide detail about the context of the suctioning alone.

Conclusions

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.

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).

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.

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.

International review of AGP lists

In supplement to the systematic review, an international review of AGP lists was undertaken by the Independent High Risk AGP Panel. Lists of AGPs were obtained from the UK, South Korea, Singapore, Denmark, Canada, the Kingdom of Saudi Arabia, South Africa, Ireland, the United States, Australia, Thailand, Ireland, Sweden, Norway and Israel. If provided, information on procedures under consideration for moving from a low to a high risk category, procedures considered low risk and those procedures in which there was uncertainty regarding aerosol production were also recorded.

Country lists were tabulated alongside the WHO and ECDC list of AGPs. This review indicated a lack of consensus among countries regarding what is considered a high risk AGP. This is reflective of the sparse evidence base on which to make decisions.

The UK list was comprehensive in comparison to other countries and broader in its inclusions than the WHO and ECDC lists, however 2 procedures (nebulisation and CPR) were common to 5 or more countries’ high risk AGP lists and are not on the UK list currently. Both have been previously considered by the UK IPC cell, which concluded that they do not currently have a strong evidence base linking them with increased risk of infection transmission. However, these may be considered high risk by some countries due to the likelihood of being performed with other high risk procedures, such as intubation or manual ventilation. The UK high risk AGP list includes intubation and ventilation, so some of these differences are about how the procedures are classified and the language used to describe them.

Further research requirements

Given the absence of evidence presented for the procedures included in this review, and for much of the AGP guidance to date, the panel considered the future research requirements for this agenda.

Clinical studies to date are poorly designed in terms of aerosol measurement and frequently lack robust conclusions in terms of particle production and transport. There is a need for better design, involving a broad range of disciplines inclusive of: infection prevention and control specialists, clinicians who perform the procedures, virology and aerosol engineering.

International guidelines for aerosol sampling and measurements are needed for AGP studies that include characterisation of the entire range of particle sizes, which are rarely measured. Standardisation of data collection and calibration against recognised standards in clinical settings is also needed to allow for pooling of data for synthesis and meta-analysis.

Clinical studies are required as the priority during the pandemic, so that the clinical risk is better understood in a timely manner, to enable any further mitigation of these risks in UK IPC guidance. The panel noted the importance of research being done from a broader AGP perspective than COVID-19 alone, however there is an urgent need for guidance for the COVID-19 pandemic.

Coordination is required with regards to ensuring that different research groups, often from different medical and dental specialties, are aware of each other’s projects and to ensure that AGP research gaps are being addressed in a timely fashion with robust, shared methodology. The NIHR Clinical Research Network AGP research task and finish group, which reports to the Urgent Public Health (UPH) Group, has started this process and this needs to be supported. This group should be formally connected to the Independent AGP panel so that emerging evidence can have a pathway to impact in national guidance at pace.

Future clinical AGP research will require a model of commissioning through coordinated calls, both nationally and internationally. It is important to discuss with funders such as United Kingdom Research and Innovation (UKRI) - cross-cutting traditional Research Council boundaries - and NIHR, and also non-UK research funders for example, the Global Research Collaboration for Infectious Disease Preparedness (GloPID R), to define and prioritise research gaps and advance a coordinated funding response.

References

1. World Health Organization (‎2014)‎. Infection prevention and control of epidemic- and pandemic-prone acute respiratory infections in health care. World Health Organization.