Modelling the direct virus exposure risk associated with respiratory events

Abstract

The outbreak of the COVID-19 pandemic highlighted the importance of accurately modelling the pathogen transmission via droplets and aerosols emitted while speaking, coughing and sneezing. In this work, we present an effective model for assessing the direct contagion risk associated with these pathogen-laden droplets. In particular, using the most recent studies on multi-phase flow physics, we develop an effective yet simple framework capable of predicting the infection risk associated with different respiratory activities in different ambient conditions. We start by describing the mathematical framework and benchmarking the model predictions against well-assessed literature results. Then, we provide a systematic assessment of the effects of physical distancing and face coverings on the direct infection risk. The present results indicate that the risk of infection is vastly impacted by the ambient conditions and the type of respiratory activity, suggesting the non-existence of a universal safe distance. Meanwhile, wearing face masks provides excellent protection, effectively limiting the transmission of pathogens even at short physical distances, i.e. 1 m.

Hybrid measurement of respiratory aerosol reveals a dominant coarse fraction resulting from speech that remains airborne for minutes

“…While our values for breathing- and vowel-generated particles are comparable to prior measurements, we find far higher speech aerosol numbers for particles 3 μm than prior studies ( 27 , 35 , 54 , 63 ). The dichotomy between these APS-based measurements and our earlier laser light scattering observations ( 32 , 52 ) was noted to strongly impact the modeled risk of virus exposure associated with respiratory events ( 41 ). Strikingly, high-quality light scattering observations by Alsved et al.…”

“…Therefore, respiratory particles rapidly dehydrate and remain airborne or fall to the bottom of the chamber prior to full evaporation of their aqueous fraction if their initial D exceeds ca. 80 μm ( 40 – 42 ). Dehydrated particles larger than ca.…”

“…Assuming the commonly used well-mixed room model ( 41 , 59 , 60 ) with a modest ventilation rate, α = 2 h −1 , and a slow virus viability decay rate, β = 1 h −1 , we can estimate the virus distribution as a function of aerosol size, following entry of an infected person into a 50-m 3 room with a 2.5-m ceiling height. Calculations include continuous tidal breathing and speaking a single “popeye” plus generating a vowel sound (1 L) once every 3 min.…”

“…Modeling analyses of well-documented superspreader events have linked the approximately known number of virions in respiratory fluid to the attack rate in susceptible persons as a function of duration of exposure, physical activity, ventilation, and other factors ( 41 , 59 , 70 ). The virus-containing aerosol mass, based on past particle counter measurements, mostly lacked the dominant coarse-aerosol fraction.…”

“…A proper, quantitative understanding of the size distribution of respiratory droplets forms the basis for all efforts at quantitative modeling of airborne virus transmission ( 41 , 59 , 60 , 70 , 79 , 80 ). Our results suggest that the quantity of speech aerosol, in particular in the 4-μm range, may have been strongly underestimated in many prior reports.…”