Exposure to a COVID-19 carrier: transmission trends in respiratory tract and estimation of infectious dose

How human respiratory physiology and inhaled airflow therein proceed to impact transmission of SARS-CoV-2, leading to the initial infection, is an open question. An answer can help determine the susceptibility of an individual on exposure to a COVID-2019 carrier and can also quantify the still-unknowninfectious dosefor the disease. Combining computational fluid mechanics-based tracking of respiratory transport in anatomic domains with sputum assessment data from hospitalized COVID-19 patients and earlier measurements of ejecta size distribution during regular speech – this study shows that the regional deposition of virus-laden inhaled droplets at the initial nasopharyngeal infection sites, located in the upper airway, peaks over the droplet size range of 2.5 – 19µ; and reveals that the number of virions that can potentially establish the infection is, at most, of𝒪(10²).