The effect of respiratory activity, ventilatory therapy and facemasks on total aerosol emissions

Wilson, N.; Marks, G.; Eckhardt, A.; Clarke, A.; Young, F.; Garden, F.; Stewart, W.; Cook, T.; Tovey, E.

Background Exhaled respirable aerosols (<5 m diameter) present a high risk of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) transmission. Many guidelines recommend using aerosol precautions during "aerosol generating procedures" (AGPs) and droplet (<5 m) precautions at other times. However, there is emerging evidence that respiratory activities such as cough and not AGPs are the important source of aerosols. Methods We used a novel chamber with an optical particle counter sampling at 100 L/min to count and size-fractionate all exhaled particles (0.5-25 m). We compared emissions from ten healthy subjects during respiratory "activities" (quiet breathing, talking, shouting, forced expiratory maneuvers, exercise and coughing) with respiratory "therapies" designated as AGPs: high flow nasal oxygen (HFNO) and single or dual circuit non-invasive positive pressure ventilation, NIPPV-S and NIPPV-D, respectively. Activities were repeated wearing facemasks. Results Compared to quiet breathing, respiratory activities increased particle counts between 34.6-fold (95% confidence interval [CI], 15.2 to 79.1) during talking, to 370.8-fold (95% CI, 162.3 to 847.1) during coughing (p<0.001). During quiet breathing, HFNO at 60 L/min increased counts 2.3-fold (95% CI, 1.2 to 4.4) (p=0.03) and NIPPV-S and NIPPV-D at 25/10 cm H2O increased counts by 2.6-fold (95% CI, 1.7 to 4.1) and 7.8-fold (95% CI, 4.4 to 13.6) respectively (p<0.001). During activities, respiratory therapies and facemasks reduced emissions compared to activities alone. Conclusion Talking, exertional breathing and coughing generate substantially more aerosols than the respiratory therapies HFNO and NIPPV which can reduce total emissions. The risk of aerosol exposure is underappreciated and warrants widespread targeted interventions.