COVID-19 and Dentistry: Aerosol and Droplet Transmission of SARS-CoV-2, and Its Infectivity in Clinical Settings

An aerosol can be defined as a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be either natural – such as fog, mist, dust, or anthropogenic – created by humans or animals when they go through normal activities, such as speaking, sneezing, or coughing, for instance. Aerosols can also be visible, like fog, but more often invisible, like dust or pollen. Irrespective of the visibility or size, they may contain live/dead microbes and hence the term bio-aerosols. It is noteworthy that aerosols can be produced indirectly (by humans) via mechanical means, such as respirators and poorly maintained air-conditioning systems. In our context, bioaerosols are the offending agents that contribute much to COVID-19 spread.

The characteristics of bio-aerosols and their spread vary considerably, depending on numerous confounding factors. There are conflicting reports in the literature on the size of the aerosols and how long they are airborne. For instance, early researchers have classified particles <100 μm in diameter as aerosols, and those >100 μm as droplets or ‘spatter/splatter’ (Figure 1). The latter usually fall on to the ground immediately after they are expelled. The former, aerosols, on the contrary, may be entrained or suspended in the air for considerable periods, depending on the humidity, airflow, and temperature of the environment into which they are expelled, such as a dental clinic operatory or a hospital ward. Similarly, the large diameter ‘droplets’, containing millions of viral particles, can contaminate surfaces in the immediate vicinity, and spread a few metres, yet again depending on the ambient conditions, such as the airflow.