The effect of respiratory activity, non‐invasive respiratory support and facemasks on aerosol generation and its relevance to COVID‐19

Abstract

Respirable aerosols (< 5 µm in diameter) present a high risk of SARS-CoV-2 transmission. Guidelines recommend using aerosol precautions during aerosol-generating procedures, and droplet (> 5 µm) precautions at other times. However, emerging evidence indicates respiratory activities may be a more important source of aerosols than clinical procedures such as tracheal intubation. We aimed to measure the size, total number and volume of all human aerosols exhaled during respiratory activities and therapies. We used a novel chamber with an optical particle counter sampling at 100 l.min -1 to count and size-fractionate close to all exhaled particles (0.5-25 µm). We compared emissions from ten healthy subjects during six respiratory activities (quiet breathing; talking; shouting; forced expiratory manoeuvres; exercise; and coughing) with three respiratory therapies (high-flow nasal oxygen and single or dual circuit non-invasive positive pressure ventilation). Activities were repeated while wearing facemasks. When compared with quiet breathing, exertional respiratory activities increased particle counts 34.6-fold during talking and 370.8-fold during coughing (p < 0.001). High-flow nasal oxygen 60 at l.min -1 increased particle counts 2.3-fold (p = 0.031) during quiet breathing. Single and dual circuit non-invasive respiratory therapy at 25/10 cm.H 2 O with quiet breathing increased counts by 2.6-fold and 7.8-fold, respectively (both p < 0.001). During exertional activities, respiratory therapies and facemasks reduced emissions compared with activities alone. Respiratory activities (including exertional breathing and coughing) which mimic respiratory patterns during illness generate substantially more aerosols than non-invasive respiratory therapies, which conversely can reduce total emissions. We argue the risk of aerosol exposure is underappreciated and warrants widespread, targeted interventions.

SARS-CoV-2 environmental contamination from hospitalised COVID-19 patients receiving aerosol generating procedures

“…The levels of environmental contamination in our study were not significantly influenced by CPAP/HFNO therapies and/or coughing. These findings broadly reflect data from aerosol generation studies in healthy adult volunteers which report non-invasive positive pressure ventilation (NIPPV) and HFNO did not generate significantly more aerosols (compared to other respiratory activities) 21 24 or in fact reduced emissions for NIPPV and HFNO 22 and CPAP 23 . This may be influenced by the semi-closed system of CPAP delivery and PEEP over the nose and mouth simultaneously that limit aerosol/droplet dispersion from respiratory secretions.…”

“…Hamilton et al report HFNO was associated with increased aerosol emission (flow rate and machine dependent), however this was generated by the machine, not the patient, hence unlikely to carry SARS-CoV-2 virus. Moreover, these studies consistently reported the highest aerosol emissions were from coughing, irrespective of respiratory support modality, with at least a 3-fold increase [21][22][23] . We did not find this signal in our data however these findings indicate that coughing is potentially the most hazardous source of infectious SARS-CoV-2 aerosols to HCWs and not the respiratory support device itself.…”

“…SARS-CoV-2 environmental contamination has been widely found in multiple studies, however very few have specifically evaluated the impact of CPAP and/or HFNO, or have found biologically viable virus that proves a transmission risk to HCWs [12][13][14][15][16][17][18][19][20] . Other studies in this field include aerosol generation studies that have mainly used patient simulators or healthy volunteers [21][22][23][24] . Here we report our observations from sampling the clinical environment of COVID-19 patients undergoing CPAP and HFNO, compared to the use of supplemental oxygen, to better understand the risks of airborne and fomite SARS-CoV-2 contamination and exposure to HCWs.…”

Healthcare Institutions’ Recommendation Regarding the Use of FFP-2 Masks and SARS-Cov-2 Seropositivity Among Healthcare Workers – A Multicenter Longitudinal Cohort Study

“…In contrast, the United States Centers for Diseases Control and Prevention (CDC), the European Centre for Disease Prevention and Control (ECDC), and the German Robert Koch Institute recommended universal use of ltering face piece class-2 (FFP-2) masks for protection against airborne transmission (19)(20)(21). Indeed, recent publications suggest that aerosols not arise only during AGP and therefore FFP-2 masks might be advantageous in virus-rich indoor environments including medical centres and hospitals (22)(23)(24).…”

Australia must act to prevent airborne transmission of SARS‐CoV‐2

“…Since the earliest days of the pandemic, respiratory droplets and fomites were assumed to be the major transmission routes, with airborne transmission only accepted within the limited confines of certain “aerosol generating procedures” 2 . In fact, this is a misnomer, because volitional coughing produces more aerosols than both invasive and non‐invasive respiratory therapies 3,4 . The experience of SARS and Middle East respiratory syndrome (MERS) should also have alerted us to the likelihood that SARS‐CoV‐2 could also be transmitted via the airborne route.…”