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. 2009 Dec 6;6 Suppl 6(Suppl 6):S703-14.
doi: 10.1098/rsif.2009.0388.focus. Epub 2009 Oct 7.

Exhaled droplets due to talking and coughing

Xiaojian Xie  1 , Yuguo Li, Hequan Sun, Li Liu
Affiliations

Exhaled droplets due to talking and coughing

Xiaojian Xie et al. J R Soc Interface. .

Abstract

Respiratory infections can be spread via 'contact' with droplets from expiratory activities such as talking, coughing and sneezing, and also from aerosol-generating clinical procedures. Droplet sizes predominately determine the times they can remain airborne, the possibility of spread of infectious diseases and thus the strategies for controlling the infections. While significant inconsistencies exist between the existing measured data on respiratory droplets generated during expiratory activities, a food dye was used in the mouth during measurements of large droplets, which made the expiratory activities 'unnatural'. We carried out a series of experiments using glass slides and a microscope as well as an aerosol spectrometer to measure the number and size of respiratory droplets produced from the mouth of healthy individuals during talking and coughing with and without a food dye. The total mass of respiratory droplets was measured using a mask, plastic bag with tissue and an electronic balance with a high precision. Considerable subject variability was observed and the average size of droplets captured using glass slides and microscope was about 50-100 microm. Smaller droplets were also detected by the aerosol spectrometer. More droplets seemed to be generated when a food dye was used.

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Figures

Figure 1.
Figure 1.
(a) Schematic diagram and (b) photo of the experimental setup.
Figure 2.
Figure 2.
Schematic diagram of slide placement in the test box.
Figure 3.
Figure 3.
Particle concentration history inside and outside the box during the entire process of one trial of coughing experiment conducted on 25 October 2006. Filled circle, diameter greater than 0.50 µm (outside the box); open diamond, diameter greater than 0.50 µm (inside the box).
Figure 4.
Figure 4.
Droplet stain mark: (a) on the slide surface when no food dye was used; (b) on the slide surface when food dye was used; (c) on a WSP.
Figure 5.
Figure 5.
Number percentages of droplet stain marks observed on different slides. Unfilled bar, talking; filled bar, coughing.
Figure 6.
Figure 6.
Cumulative percentage of droplets less than the stated diameter produced by talking and coughing (T-S, talking experiment with food dye with sugar used; T-D, talking experiment with food dye used; T-N, talking experiment without food dye; C-N, coughing experiment without food dye).
Figure 7.
Figure 7.
Percentage µm−1 versus droplet diameter detected on the sampling slides: (a) talking (T-N, talking experiment without food dye (filled square); T-D, talking experiment with food dye used (filled star); T-Duguid, talking experiment in Duguid (1946) (open circle); T-L&R, talking experiment in Loudon & Roberts (1967) (open triangle)); (b) coughing (C-N, coughing experiment without food dye (filled square); C-Duguid, coughing experiment in Duguid (1946) (open circle); C-L&R, coughing experiment in Loudon & Roberts (1967) (open triangle)). (Note: see the discussion in the text on the calculation of the vertical axis value.)
Figure 8.
Figure 8.
Relationship between droplet size at the origin and droplet size on the sampling slide. Black line, ground wall of the box; dashed line, Y = X.
Figure 9.
Figure 9.
Percentage µm−1 versus droplet diameter estimated at the origin: (a) talking (T-N, talking experiment without food dye (filled square); T-D, talking experiment with food dye used (filled star); T-Duguid, talking experiment in Duguid (1946) (open circle); T-L&R, talking experiment in Loudon & Roberts (1967) (open triangle)); (b) coughing (C-N, coughing experiment without food dye (filled square); C-Duguid, coughing experiment in Duguid (1946) (open circle); C-L&R, coughing experiment in Loudon & Roberts (1967) (open triangle)). (Note: see the discussion in the text on the calculation of the vertical axis value.)
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