COVID-19: An Aerosol's Point of View from Expiration to Transmission to Viral-mechanism

AIRBORNE According to WHO (2020b), SARS-CoV-2 is primarily transmitted by respiratory droplets produced by sneezing and coughing from an infected person, either directly when the droplets reach a person’s nose, mouth or eyes, or indirectly when a person touches a droplet-contaminated surface or inanimate object (i.e., fomite) and then touches his/her nose, mouth or eyes. [...]widely advocated preventive measures against SARS-CoV-2 infection, such as wearing masks, frequent hand washing and social distancing, are meant to minimize transmission from nearby infected persons. Another unique characteristic associated with smaller droplet nuclei is the increased ease of inhalation deeper into the human respiratory tract, with decreasing particle size. [...]airborne transmission is of particular concern; however, the biological implications of airborne transmission in COVID-19 are currently still unclear. First and foremost, it is critical to note that transmission is not the only factor determining whether or not a person will be infected by SARS-CoV-2. A comprehensive infection risk assessment demands more factors for consideration, including the virus (e.g., viability and infectious dose), infected person (e.g., viral load), transmission mode (droplet vs. airborne), aerosol processes (e.g., phase transformation and respiratory deposition), the medium (e.g., building ventilation and transport processes) and host (e.g., immune system and use of personal protection equipment), and integrates the risks from source to receptor.