Virus transmission by aerosol transport during short conversations

Abstract

The SARS-CoV-2 is transmitted not only through coughing, but also through breathing, speaking or singing. We perform direct numerical simulations of the turbulent transport of potentially infectious aerosols in short conversations, involving repetitive phrases separated by quiescent intervals. We estimate that buoyancy effects due to droplet evaporation are small, and neglect them. A two-way conversation is shown to significantly reduce the aerosol exposure compared with a relative monologue by one person and relative silence of the other. This is because of the ‘cancelling’ effect produced by the two interacting speech jets. Unequal conversation is shown to significantly increase the infection risk to the person who talks less. Interestingly, a small height difference is worse for infection spread, due to reduced interference between the speech jets, than two faces at the same level. For small axial separation, speech jets show large oscillations and reach the other person intermittently. We suggest a range of lateral separations between two people to minimize transmission risk. A realistic estimate of the infection probability is provided by including exposure through the eyes and mouth, in addition to the more common method of using inhaled virions alone. We expect that our results will provide useful inputs to epidemiological models and to disease management.

From Microscopic Droplets to Macroscopic Crowds: Crossing the Scales in Models of Short‐Range Respiratory Disease Transmission, with Application to COVID‐19

“…[53] Risk assessment must also involve a model for inhalation. In simulations, specific areas (nose, mouth, eyes) that can be impacted or traversed by droplets may be marked in the simulation domain, in order to gauge the relative risks raised by droplet impact and inhalation [5,48] or to quantify the protective effect of the exhalation of the susceptible person in a conversation, [49,51] for instance. The inhalation volume of a passive scalar may also be used to assess the risk.…”

From microscopic droplets to macroscopic crowds: Crossing the scales in models of short-range respiratory disease transmission, with application to COVID-19

“…Numerical studies provide a means to circumvent these limitations; indeed, their replicability enables researchers to test assumptions, investigate the effect of different parameters, relate behaviors to transmission risks and build a mechanistic picture of the risks in such contexts. The COVID-19 pandemic has prompted an unprecedented effort from the fluid mechanics community to probe the transport of respiratory droplets after their emission, in particular using CFD [13,14,30,[47][48][49][50], which has shed light on the sensitivity of this propagation to the environment [13][14][15]. Simulations have thus considered diverse environmental settings, as well as diverse expiratory events, including coughing [13,49,51], sneezing [15,51], speaking [14,30,49,51] and breathing [30].…”

“…In simulations, specific areas (nose, mouth, eyes) that can be impacted or traversed by droplets may be marked in the simulation domain, in order to gauge the relative risks raised by droplet impact and inhalation [4,47] or to quantify the protective effect of the exhalation of the susceptible person in a conversation [48,50], for instance. The inhalation volume of a passive scalar may also be used to assess the risk [53].…”

“…Leaving aside inhalation, the local concentration of virus in a region of interest may be monitored, as a proxy for the infection risk [15]; the need to simulate the susceptible person at each position that they may occupy is thus bypassed. Time may be involved by comparing the quantity of inhaled virus over time to an infectious dose [14,47,48,50,54,55] via a dose-response model [56,57]. This quantity can be measured in absolute terms, as a number of viral copies, which requires specifying the viral titer in the emitter's respiratory fluids and the minimal infectious dose, or in terms of quanta of infection, if the number of emitted virus is rescaled by the infectious dose [19].…”

A computational fluid dynamics—Population balance equation approach for evaporating cough droplets transport

“… Diwan et al (2020) adopted DNS to study the evolution of the cough or sneeze flows without droplets. In their later works, they coupled E–E approach with DNS to investigate the dispersion of small cough droplets ( ) ( Singhal et al, 2021 ) and the virus transmission during short conversations ( Singhal et al, 2022 ). For RANS method, Yan et al (2020) compared the two-fluid model (TFM), one kind of E–E approach, with E–L approach in their study on the transport of non-evaporating aerosols (0.2, 0.77 and ) in a ventilated room.…”