Collection, particle sizing and detection of airborne viruses

Abstract

Viruses that affect humans, animals and plants are often dispersed and transmitted through airborne routes of infection. Due to current technological deficiencies, accurate determination of the presence of airborne viruses is challenging. This shortcoming limits our ability to evaluate the actual threat arising from inhalation or other relevant contact with aerosolized viruses. To improve our understanding of the mechanisms of airborne transmission of viruses, air sampling technologies that can detect the presence of aerosolized viruses, effectively collect them and maintain their viability, and determine their distribution in aerosol particles, are needed. The latest developments in sampling and detection methodologies for airborne viruses, their limitations, factors that can affect their performance and current research needs, are discussed in this review. Much more work is needed on the establishment of standard air sampling methods and their performance requirements. Sampling devices that can collect a wide size range of virus-containing aerosols and maintain the viability of the collected viruses are needed. Ideally, the devices would be portable and technology-enabled for on-the-spot detection and rapid identification of the viruses. Broad understanding of the airborne transmission of viruses is of seminal importance for the establishment of better infection control strategies.

Keywords: aerosol; aerovirology; air sampler; airborne transmission; collection efficiency; size distribution.

Figure 1

Comparison between droplet transmission () and aerosol transmission (). Large droplets settle close to the source, while smaller aerosol particles stay aloft and can drift long distances. Once inhaled, very small particles can reach deeper to the pulmonary region while larger particles are captured in the nasopharyngeal region in the upper respiratory system. [Colour figure can be viewed at http://wileyonlinelibrary.com]

Figure 2

Conceptual schematic diagrams of various air samplers for airborne viruses and their collection mechanisms. Solid circles (•) are aerosol particles and the size of the circle indicates the size of the particle (not in scale). Shown are an impactor, cyclone, filter, impinger, electrostatic precipitator and a water‐based growth tube collector. Impactor: particles in the incoming airstream accelerate through small nozzles (in the form of holes or slits), and those with high inertia impact onto the surface of collection media. Cascade Impactor: by successively decreasing nozzle size, particles are classified by their inertia to be collected onto different size stages. Cyclone: centrifugal forces deviate particles from the air flow to impact onto the collection wall. Impinger: Abrupt change in the airstream direction inside the bottle impacts particles into the liquid collection medium. Filtration: Particles are collected onto filter media through interception, inertial impaction, and diffusion. Electrostatic precipitator: Particles are first charged through corona discharge to create electrostatic attraction that draws the charged particles to collection plates (oppositely charged). Water‐based growth tube collector: Cold aerosol particles are introduced into a warm growth tube saturated with water vapour. This process encapsulates small particles into larger droplets, thus enabling efficient collection of these enlarged particles through gentle impaction. [Colour figure can be viewed at http://wileyonlinelibrary.com]