Transmission of COVID-19 by droplets and aerosols
COVID-19 is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). As is the case with many other respiratory viruses, COVID-19 is believed to be transmitted from human-to-human by droplets, aerosols, and objects such as clothes, utensils and furniture (‘fomites’).
The subject of infection transmission by viruses through droplets and aerosols remains poorly understood. Typically, people who are infected will spread viral particles whenever they talk, breathe, cough, or sneeze.
These viral particles are compressed in globules of mucus, saliva, and water. Some of these globules are too heavy to remain in the air and fall on nearby floors or surfaces as droplets. Fomites collect droplets contaminated with the COVID-19 virus; and when such surfaces are touched, infection can be rapidly passed on. The smaller droplets evaporate faster and convert to aerosol particles with relatively smaller aerodynamic diameters and linger in the air farther away than the droplets.
Respiratory particles may often be distinguished to be droplets or aerosols based on the particle size and aerodynamic diameter. (The World Health Organization (WHO) and Centres for Disease Control and Prevention (CDC) postulate the particles of more than 5 microns as droplets, and those less than 5 microns as aerosols or droplet nuclei).
Findings from several studies confirm that breathing and exhalation originating from the nose can shed up to a few hundreds of droplets of which some may be aerosols; in contrast, talking, coughing, and sneezing produce more aerosols than droplets. The transmission of droplets and aerosols has significant implications on healthcare workers and carers managing patients infected with COVID-19, and using appropriate personal protective equipment is of utmost importance.
The efficacy of specific types of personal protective equipment (PPE) in combating the transmission of the SARS-CoV-2 continues to be researched with face coverings/masks believed to have a major role in preventing infection transmission. The use of face coverings/masks is believed to control the:
a) penetration of droplets from an infectious person to a susceptible host
b) droplets going out from an infected patient
Despite current guidance, the effectiveness of face coverings and masks in controlling SARS-CoV-2 transmission remains uncertain. Different commercial masks have been found to have varying efficiencies in controlling the transmission of infectious agents. No single mask is guaranteed to cut off the transmission of infection from the SARS-CoV-2 fully.
The practice of social distancing and adequate respiratory / hand etiquette remain of prime importance in the global combat against the spread of COVID-19.