In the early days of the coronavirus 2019 (COVID-19) pandemic, the topic of aerosol-generating procedures (AGPs) was a focus of concern to promote infection control and health care professional safety. The issue of which providers were more frequently exposed to AGPs, and thus at greater risk of infection, weighed heavily in decisions regarding the distribution of personal protective equipment (PPE) for health care staff.
Certain medical interventions such as intubation, tracheotomy, and bronchoscopy have been designated as AGPs by various public health agencies and professional medical societies, although no consensus has been established regarding the specific interventions that constitute AGPs.1 However, the authors of several recent papers have questioned the utility of the AGP concept altogether, noting that the distinction between AGPs and other potentially high-risk scenarios is largely based on epidemiologic observations and theoretical assumptions.1-3
Since the onset of COVID-19, researchers have produced surprising findings that challenge previous beliefs about AGPs. Studies have found that sampled aerosol concentrations from several designated AGPs were similar to those generated by speaking and tidal breathing.2 Research has also shown that volitional coughing generated a substantially higher amount of aerosols compared to bronchoscopy, noninvasive ventilation, and controlled intubations and extubations.1
Based on the available evidence, a “coughing patient with acute COVID-19 is likely to generate more infectious aerosol than many AGPs,” although further investigation is needed to fully clarify the risk related to various procedures across a range of settings.2
As the science of respiratory transmission has evolved, it “has become clear that the traditional dichotomy between droplet vs aerosol-based transmission is overly simplistic,” according to paper published in 2020 by Michael Klompas, MD, MPH, infectious disease physician and hospital epidemiologist at Brigham and Women’s Hospital and professor of population medicine at Harvard Medical School in Boston, Massachusetts, and colleagues1
“In practice, people routinely produce a profusion of respiratory particles in a range of sizes that include both droplets and aerosols as well as particles in between,” the authors wrote, all of which can carry and potentially transmit viral particles.1
In a paper published in July 2021 in The Lancet Respiratory Medicine, Hamilton et al proposed an evidence-based framework for risk evaluation based on the main factors driving the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission: physical exposure to individuals with suspected or confirmed infection, with consideration of symptoms, vaccination status, and other relevant factors; proximity to the patient; duration of exposure; health care provider risk in terms of age, sex, comorbidities, and vaccination status; and environmental risk posed by ventilation, temperature, and humidity within the health care setting.2
These factors are similar to those recommended by Klompas et al, who also advised consideration of the amount of air being forced across the respiratory mucosa in a given activity (eg, heavy breathing or coughing) or procedure (eg, positive pressure ventilation, high-flow oxygen, or spirometry). They stated that the term AGP is a misnomer, as the risk of transmission does not stem from a particular procedure but rather these specified circumstances surrounding the intervention.1
Overall, the emerging data suggest that “many currently defined AGPs are unlikely to play any significant role in generation of infectious aerosol that poses a risk to staff,” and thus “the term AGP has neither face validity nor construct validity” wrote Hamilton et al.2 “Instead, we should focus on the risk in plain sight: close, physical exposure to people suspected, or known to have, COVID-19 for prolonged time or where ventilation remains poor.”
We interviewed Dr Klompas to for additional discussion regarding the latest developments and remaining needs in this area.
How is our understanding of AGPs changing in the context of COVID-19?
COVID-19 has catalyzed a wave of studies measuring the amount of aerosols generated during various procedures rather than simply making assumptions about aerosol generation. Remarkably, these studies have consistently found that just about every procedure we have classically characterized as aerosol-generating in fact generates little or no additional aerosols above and beyond the patient’s baseline rate of generation. This includes intubation, extubation, high flow oxygen via nasal cannula, and noninvasive positive pressure ventilation.
Conversely, some procedures that historically were never considered aerosol-generating turn out to generate plenty of aerosols, including exercise, forced expiration, and coughing. The only traditional AGP that has consistently been associated with large amounts of aerosol generation is nebulization, and, in that case, the majority of the aerosols are medication rather than respiratory secretions.
What are the relevant implications for clinicians, hospital and practice administrators, and other stakeholders?
This updated understanding of aerosol generation has massive implications for the steps we take to protect health care workers and other patients from respiratory viruses. It means that reserving N95 respirators for so-called AGPs makes no sense because these are not the sources of aerosol generation. Coughing and labored breathing are greater sources of risk.
We should therefore retire the concept of AGPs and teach clinicians instead that transmission risk is a function of viral load, proximity, duration of exposure, and quality of ventilation. N95 respirators or their equivalents are indicated for all sustained exposures with patients with possible or confirmed respiratory viral infections, not just encounters with so-called AGPs.
There may also be a role for universal use of N95 respirators in health care when community COVID-19 incidence rates are high and thus the risk of any patient or colleague being a silent carrier is significant.
In light of these developments, what are the most critical priorities in this area?
We need to undertake a wholescale re-evaluation of our approach to preventing respiratory virus transmission. If we fail to get the science of transmission right, then we are bound to see breakthroughs and outbreaks.
1. Klompas M, Baker M, Rhee C. What Is an aerosol-generating procedure? JAMA Surg. 2021;156(2):113-114. doi:10.1001/jamasurg.2020.6643
2. Hamilton F, Arnold D, Bzdek BR, et al; AERATOR group. Aerosol generating procedures: are they of relevance for transmission of SARS-CoV-2? Lancet Respir Med. 2021;9(7):687-689. doi:10.1016/S2213-2600(21)00216-2
3. Harding H, Broom A, Broom J. Aerosol-generating procedures and infective risk to healthcare workers from SARS-CoV-2: the limits of the evidence. J Hosp Infect. 2020;105(4):717-725. doi:10.1016/j.jhin.2020.05.037