Short-range airborne route dominates exposure of respiratory infection during close contact

Abstract

A susceptible person experiences the highest exposure risk of respiratory infection when he or she is in close proximity with an infected person. The large droplet route has been commonly believed to be dominant for most respiratory infections since the early 20 th century, and the associated droplet precaution is widely known and practiced in hospitals and in the community. The mechanism of exposure to droplets expired at close contact, however, remains surprisingly unexplored. In this study, the exposure to exhaled droplets during close contact (< 2 m) via both the short-range airborne and large droplet sub-routes is studied using a simple mathematical model of expired flows and droplet dispersion/deposition/inhalation, which enables the calculation of exposure due to both deposition and inhalation. The shortrange airborne route is found to dominate at most distances studied during both talking and coughing. The large droplet route only dominates when the droplets are larger than 100 μm and when the subjects are within 0.2 m while talking or 0.5 m while coughing. The smaller the exhaled droplets, the more important the short-range airborne route. The large droplet route contributes less than 10% of exposure when the droplets are smaller than 50 μm and when the subjects are more than 0.3 m apart, even while coughing. Keywords: exposure, disease transmission, close contact, short-range airborne, large droplet Practical implications Our simple but novel analysis shows that conventional surgical masks are not effective if most infectious viruses are contained in fine droplets, and non-conventional intervention methods such as personalised ventilation should be considered as infection prevention strategies given the possible dominance of the short-range airborne route, although further clinical evidence is needed. Nomenclatureefficiency [-] Exposure due to large droplet route [μL] Exposure due to short-range airborne route [μL] Gravitational acceleration [m•s -2 ] Mass current [kg•s -1 ] IF Inhalation fraction [-] Constant (=0.3) [-] Thermal conductivity of air [W•m -1 •K -1 ] LS Exposure ratio between large droplet and short-range airborne [-] Latent heat of vaporization [J•kg -1 ] Droplet mass [kg] Mass of liquid in a droplet [kg] Mass of solid in a droplet [kg] 0 Jet initial momentum [m 4 •s -2 ] Molecular weight of H2O [kg•mol -1 ] MF Membrane fraction [-] n Number of droplets [n] 0 Number of droplets expelled immediately at mouth [n] Number of droplets entering the inhalation zone [n] Number of droplets potentially deposited on mucous membranes [n] Total number of released droplets [n] Nu Nusselt number [-] p Total pressure [Pa].

The economic value of quarantine is higher at lower case prevalence, with quarantine justified at lower risk of infection

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Effects of the COVID-19 lockdown on criteria air pollutants in the city of Daegu, the epicenter of South Korea’s outbreak

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Facemask Alternatives in Veterinary Medicine in the Context of COVID-19 Shortages

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