The Fluid Dynamics of Disease Transmission

Abstract

For an infectious disease such as the coronavirus disease 2019 (COVID-19) to spread, contact needs to be established between an infected host and a susceptible one. In a range of populations and infectious diseases, peer-to-peer contact modes involve complex interactions of a pathogen with a fluid phase, such as isolated complex fluid droplets or a multiphase cloud of droplets. This is true for exhalations including coughs or sneezes in humans and animals, bursting bubbles leading to micron-sized droplets in a range of indoor and outdoor settings, or impacting raindrops and airborne pathogens in foliar diseases transferring pathogens from water to air via splashes. Our mechanistic understanding of how pathogens actually transfer from one host or reservoir to the next remains woefully limited, with the global consequences that we are all experiencing with the ongoing COVID-19 pandemic. This review discusses the emergent area of the fluid dynamics of disease transmission. It highlights a new frontier and the rich multiscale fluid physics, from interfacial to multiphase and complex flows, that govern contact between an infected source and a susceptible target in a range of diseases. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 53 is January 6, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Growth and breakup of ligaments in unsteady fragmentation

“…An important class of fragmentation processes forming spray in nature, industry and health is unsteady with droplets shed continuously and with properties varying over time (Yarin 2006; Traverso et al. 2013; Bourouiba, Dehandschoewercker & Bush 2014; Gilet & Bourouiba 2014,2015; Josserand & Thoroddsen 2016; Lejeune, Gilet & Bourouiba 2018; Wang & Bourouiba 2018; Bourouiba 2020). The entire sheet-mediated fragmentation of such unsteady systems can be summarized into four steps: (i) a fluid bulk (jet or drop) transforms into a sheet expanding and then retracting with time-varying deceleration; (ii) destabilization of the rim bounding the sheet with formation of corrugation on it; (iii) corrugation to ligament transition; (iv) droplet shedding from the ligament, one droplet at a time, via end-pinching (Wang & Bourouiba 2018) (figure 1).…”

Aerosol formation due to a dental procedure: insights leading to the transmission of diseases to the environment

“…The experimental techniques can also be employed as a technique to directly measure the droplet size and distributions in coughing, sneezing, talking and speaking [30,31] as there are already several studies that examined the droplet size distribution using indirect measurements where they all have their own restrictions [31]. It should also be noted that the splatters and droplets formed by the CUS are generally composed of suspended droplets of varying sizes and of the surrounding atmosphere, which is hot/cold and moist.…”

“…In this study, we use state-of-the-art experimental fluid mechanics tools, namely optical flow tracking velocimetry (OFTV) and shadowgraphy, to investigate the original formation of droplets created by a Cavitron Select SPS Ultrasonic Scaler (CUS) during the scaling process. Several researchers have previously examined the sizes of droplets using various methods during sneezing, coughing, talking and breathing [20][21][22][23][24][25][26][27][28][29][30][31]. However, to the best of the authors' knowledge, this study is the first of its kind to investigate droplet nuclei size and velocity distribution in detail using quantitative methods and the implementation of dental instruments.…”

Host-to-Host Airborne Transmission As a Multiphase Flow Problem For Science-Based Social Distance Guidelines

“…Most importantly, the results of the simple model presented in (31) and (32) are in excellent agreement with those obtained from Monte-Carlo simulation. The increasing size of the contaminated cloud with time can be predicted with (38) and the centroid is given by the scaling law (16). Figure 14: Droplet/aerosol concentration evolution as predicted by the analytical model presented in (31) and (32).…”

“…Only the drag on the puff has a significant effect in reducing the distance traveled by the puff. It can then be taken that the puff evolution to good accuracy can be represented by (16). Over a time span of 10 nondimensional units the puff has traveled about 0.7s e and the velocity has dropped to about 15% of the initial velocity.…”