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

Abstract

COVID-19 pandemic has strikingly demonstrated how important it is to develop fundamental knowledge related to generation, transport and inhalation of pathogen-laden droplets and their subsequent possible fate as airborne particles, or aerosols, in the context of human to human transmission. It is also increasingly clear that airborne transmission is an important contributor to rapid spreading of the disease. In this paper, we discuss the processes of droplet generation by exhalation, their potential transformation into airborne particles by evaporation, transport over long distances by the exhaled puff and by ambient air turbulence, and final inhalation by the receiving host as interconnected multiphase flow processes. A simple model for the time evolution of droplet/aerosol concentration is presented based on a theoretical analysis of the relevant physical processes. The modeling framework along with detailed experiments and simulations can be used to study a wide variety of scenarios involving breathing, talking, coughing and sneezing and in a number of environmental conditions, as humid or dry atmosphere, confined or open environment. Although a number of questions remain open on the physics of evaporation and coupling with persistence of the virus, it is clear that with a more reliable understanding of the underlying flow physics of virus transmission one can set the foundation for an improved methodology in designing case-specific social distancing and infection control guidelines.

Modes of Transmission of Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) and Factors Influencing on the Airborne Transmission: A Review

“…Bourouiba et al illustrated that, depending on the patient’s physiological composition (droplets of mucosalivary liquid emissions associated with hot and moist air) and meteorological conditions (humidity and temperature), the gas cloud and its payload of pathogen-bearing droplets in any size can be transmitted up to 8 m [ 64 ]. Along the way, droplets of any size can settle out or evaporate at rates that depend not only on their size but also on the degree of turbulence and velocity of the gas cloud, along with the properties of the ambient environment (temperature, humidity, and air flow) [ 64 , 65 , 66 ]. Chong et al reported that smaller respiratory droplets (<10 µm) have the tendency to be taken via the turbulent puff and travel together with the fluid.…”

“…Additionally, Fiorillo et al suggested that health care workers must be protected from the contact with the patient’s aerosol with filtering facepiece particles masks (FFP) of type FFP2 and FFP3 [ 74 ] of similar performance to N95 and N99 masks in the United States, respectively. In the case of surgical mask, their filtration efficiency only protects the user against droplet nuclei of size larger than 2 μm [ 65 ]. In general, face coverings are more effective for decreasing the direct ejection of breath and bioaerosols away from the user [ 108 ].…”

Risk Assessment of COVID-19 Airborne Infection During Hybrid Learning

“…Stronger and stronger evidence suggest that the respiratory particles emitted during a sneeze or cough are initially transported as a turbulent cloud that consists of hot and moist exhaled air and mucosalivary filaments [13, 14]. Numerical simulations and analytic studies show that aerosols and small droplets trapped inside the turbulent puff cloud could propagate up to 7 or 8 m [15–18]. Besides, once the cloud slows down sufficiently, and its coherence is lost, the eventual spreading of the infected aerosols becomes dependent on the ambient air currents and turbulence.…”

Human body heat shapes the pattern of indoor disease transmission

“…Surprisingly, little is known on long-time dispersion and transmission pattern of suspended viral particles in indoor environment. Such physical process of spreading is subtle as it involves interactions between respiratory droplets, turbulent eddies, vapor and temperature fields (1,28,(35)(36)(37)(38)(39), and also relates to several environmental factors such as ventilation (40)(41)(42)(43), ambient temperature (44,45) and relative humidity (46)(47)(48)(49)(50). In practice, ventilation is considered as an active control strategy to transport and exhaust those viral aerosols or droplets.…”