A review on the transmission of COVID-19 based on cough/sneeze/breath flows

Abstract

COVID-19 pandemic has recently had a dramatic impact on society. The understanding of the disease transmission is of high importance to limit its spread between humans. The spread of the virus in air strongly depends on the flow dynamics of the human airflows. It is, however, known that predicting the flow dynamics of the human airflows can be challenging due to different particles sizes and the turbulent aspect of the flow regime. It is thus recommended to present a deep analysis of different human airflows based on the existing experimental investigations. A validation of the existing numerical predictions of such flows would be of high interest to further develop the existing numerical model for different flow configurations. This paper presents a literature review of the experimental and numerical studies on human airflows, including sneezing, coughing and breathing. The dynamics of these airflows for different droplet sizes is discussed. The influence of other parameters, such as the viscosity and relative humidity, on the germs transmission is also presented. Finally, the efficacy of using a facemask in limiting the transmission of COVID-19 is investigated.

Fig. 1

Comparison of natural clouds (left) with cumulus clouds (right) [26]

Fig. 2

a Computational domain schematic. b Flow rate variation during a single cough event [25]

Fig. 3

Simulation of “dry cough”: temperature distribution at two time instants a at 0.86 s, b 9.37 s [25]

Fig. 4

a Fragmentation process schematic of a liquid in response to aerodynamic forces, b photograph of sneeze ejecta [70, 74]

Fig. 5

Experimental setup schematic that used to record sneezes image [70, 74]

Fig. 6

High-speed imaging of cough recording at 1000 f.p.s at a 0.005 s, b 0.008 s, c 0.015 s, d 0.032 s, e 0.15 s. [70, 74]

Fig. 7

A subject with a mask holding the spirometer during test [38]

Fig. 8

PIV Setup (VanSciver et al. 2011)

Fig. 9

PIV of Cough flow (VanSciver et al. 2011)

Fig. 10

Three temporal profiles at the nozzle exit [98, 102]

Fig. 11

Schematic diagram of the test apparatus [98, 102]

Fig. 12

Streak pictures of particles (Pulsation, Re = 12,900). The red dashed line indicates the jet boundary. The pictures overlap from t = 0 to (A) the time when the jet is interrupted (t = t_inj), and (B) t = 10t_inj [98, 102]

Fig. 13

The leading vortex is illustrated by red arrows, and white arrows indicate the particle motion [98, 102]

Fig. 14

Thermal manikin and test points (Zhang et al. 2019)

Fig. 15

Schematic of Schlieren optical imaging system set-up [84]

Fig. 16

Digitized shadowgraph image of a human volunteer coughing [83]

Fig. 17

Experimental setup used to capture droplets expelled during a sneeze (Bahl et al. 2020)

Fig. 18

Schematic of experimental platform (Feng et al. 2015)

Fig. 19

Humid puff propagation at different ambient RH [21]

Fig. 20

Qualitative comparison of airflows: coughs covered by a a tissue, b a cupped hand, c an elbow with a sleeve, d an elbow without a sleeve, and e a fist; and uncovered coughs with f average velocity and g maximum velocity [14]

Fig. 21

A subject coughing in a cyclic incident. With and without a mask (Dbouk and Drikatis 2020)