Face coverings and respiratory tract droplet dispersion

Abstract

Respiratory droplets are the primary transmission route for SARS-CoV-2, a principle which drives social distancing guidelines. Evidence suggests that virus transmission can be reduced by face coverings, but robust evidence for how mask usage might affect safe distancing parameters is lacking. Accordingly, we set out to quantify the effects of face coverings on respiratory tract droplet deposition. We tested an anatomically realistic manikin head which ejected fluorescent droplets of water and human volunteers, in speaking and coughing conditions without a face covering, or with a surgical mask or a single-layer cotton face covering. We quantified the number of droplets in flight using laser sheet illumination and UV-light for those that had landed at table height at up to 2 m. For human volunteers, expiratory droplets were caught on a microscope slide 5 cm from the mouth. Whether manikin or human, wearing a face covering decreased the number of projected droplets by less than 1000-fold. We estimated that a person standing 2 m from someone coughing without a mask is exposed to over 10 000 times more respiratory droplets than from someone standing 0.5 m away wearing a basic single-layer mask. Our results indicate that face coverings show consistent efficacy at blocking respiratory droplets and thus provide an opportunity to moderate social distancing policies. However, the methodologies we employed mostly detect larger (non-aerosol) sized droplets. If the aerosol transmission is later determined to be a significant driver of infection, then our findings may overestimate the effectiveness of face coverings.

Effects of surgical masks on aerosol dispersion in professional singing

“…For the visualization of the ballistic droplets in the diameter range larger than 5 μm [ 1 ], the singer performed the two tasks with and without mask within a dark chamber that was also installed in the BR television studio. Similar to the study of speaking and coughing in [ 45 ], the droplets were illuminated by a laser light sheet that was positioned in a sagittal orientation immediately in front of the singer subject as shown in Fig. 1 .…”

“…The frame rate amounted to 2000 Hz. The dimensions of the ROI amounted to ROI x × ROI z = 48 × 76 mm 2 which was resolved by 1280 × 800 pixels yielding a pixel resolution of ~60 μm/pixels which constitutes a similar resolution as applied by [ 45 ] for speaking and coughing and commonly used in PIV measurements [ 33 , 46 ] classically using tracer particles in the range of 1–5 μm in diameter. Thus, the setup enabled to detect particles with diameters down to 10 μm although the actual size cannot be determined for droplets being smaller than resolution of 60 μm/pixel.…”

Assessing the Impact of Mask Usage on COVID-19 Transmission Using a Computer Simulation

“…In previous studies, [17][18][19] mask usage was an independent factor that was associated with an increased odds of transmission control with an odds ratio of 3.5. 19 Based on the significant reduction in infections at 50% mask usage for 5% initial infection and the linear model for 10% initial infection, mask use should be encouraged due to the direct effect it has on reducing new infections.…”

Laboratory Modeling of SARS-CoV-2 Exposure Reduction Through Physically Distanced Seating in Aircraft Cabins Using Bacteriophage Aerosol — November 2020

“…It is important to recognize that the current study addresses only exposure and not transmission. ¶ ¶ ¶ The impact of masking also was not considered in the current aerosol analysis because masks are more effective at reducing fomite and droplet exposures than aerosol exposures (8,9). A case study of COVID-19 transmission on a flight with mandated mask wearing (10) suggests that some virus aerosol is emitted from an infectious masked passenger, such that distancing could still be useful.…”