Role of bioaerosol in virus transmission and material-based countermeasures

Abstract

Respiratory pathogens transmit primarily through particles such as droplets and aerosols. Although often overlooked, the resuspension of settled droplets is also a key facilitator of disease transmission. In this review, we discuss the three main mechanisms of aerosol generation: direct generation such as coughing and sneezing, indirect generation such as medical procedures, and resuspension of settled droplets and aerosols. The size of particles and environmental factors influence their airborne lifetime and ability to cause infection. Specifically, humidity and temperature are key factors controlling the evaporation of suspended droplets, consequently affecting the duration in which particles remain airborne. We also suggest material-based approaches for effective prevention of disease transmission. These approaches include electrostatically charged virucidal agents and surface coatings, which have been shown to be highly effective in deactivating and reducing resuspension of pathogen-laden aerosols.

Keywords: COVID‐19; bioaerosol; nanomaterial; respiratory droplet; resuspension; secondary aerosolization.

FIGURE 1

Modes of transmission. Bioaerosol can disseminate virus particles and induce the infection over long distances beyond 1 m. Bioaerosols are generated in three different ways: (1) Direct generation of bioaerosols from the infected individuals during coughing, sneezing, talking, or even normal breathing; (2) indirect generation during toilet flushing and medical procedures such as mechanical ventilation, intubation, and cardiopulmonary resuscitation; (3) Resuspension of settled droplets due to the mechanical forces produced during walking, vacuum cleaning, doffing of protective apparels, or high airspeed of exhaust fans

FIGURE 2

Trajectory, settling time, and conversion of respiratory droplets to droplet nuclei. Respiratory events such as sneezing and coughing generate a population of virus‐laden droplets of different sizes, namely large droplets (>100 um), small droplets (<5 um), and droplet nuclei (<1 um). Larger droplets experience gravitational forces and settle down at 1 m within a short time of 5 s. Small droplets can remain in the air for 30 min and travel beyond 1 m. These droplets may also undergo evaporation and decrease in size to form droplet nuclei or bioaerosols. Droplet nuclei drift in the atmosphere for a prolonged duration (12 h) up to 45 m and pose a high risk of infections at long range

FIGURE 3

Events leading to the resuspension of bioaerosol. Resuspended virus‐laden particles can act as a secondary source of infections in indoor and outdoor settings. Particles are propelled off the substrate through mechanical vibrations or high air vortices experienced at the surface and suspended in air. (A) Air swirls generate around the legs while a person walks; (B) vibrational forces during doffing of personal protective equipment; (C) mechanical vibrations on floor surfaces from vacuum cleaning can lift the particles in the air. High air velocity and turbulence generated from the (D) door opening movements, (E) ventilation windows, and (F) exhaust fans re‐aerosolize the deposited droplets into the atmosphere. Air exchange leads to the propagation of virus particles into another room or outside environment, increasing the incidence of infection spread