Aerosols and droplets containing particles that are <100 μm in diameter are not visible to the naked eye. Laboratory workers may not be aware that such particles can be generated during many laboratory procedures and that these particles could be inhaled or could cross-contaminate work surfaces, materials, and equipment.
In situations where aerosols and droplets may be produced and respiratory protection such as an N95 respirator (requires fit testing) or a BSC are not available, a physical barrier such as a splash shield while using a surgical mask may be considered. When available, a Class II BSC is recommended for procedures with a high likelihood to generate aerosols or droplets. When a BSC is not available, use additional precautions based on a laboratory-specific and activity-specific determined risk assessment and mitigation to provide a barrier between the specimen and personnel.
Droplets traditionally are defined as larger infectious particles (>5 μm in diameter) that rapidly fall out of the air, contaminating gloves, the immediate work area, and the mucous membranes of the persons performing the procedure. Examples of infectious agents that are transmitted via the droplet route include Bordetella pertussis, influenza viruses, adenovirus, Mycoplasma pneumoniae, group A Streptococcus, Neisseria meningitidis, SARS-CoV, and SARS-CoV-2.
Droplet nuclei are the residue of dried droplets that may remain suspended in the air for long periods, may be blown over great distances, and are easily inhaled into the lungs and exhaled. Droplet spread is the direct transmission of an infectious agent from a reservoir to a susceptible host by spray with relatively large, short-ranged aerosols produced by sneezing, coughing, or talking.
Infectious aerosols are small liquid or solid particles suspended in the air that contain infectious agents. They can disperse throughout the laboratory and remain infective over time and distance. These particles are of a size that may be inhaled into the lower respiratory tract (<5 μm in diameter). Examples of organisms transmitted by aerosols include spores of Aspergillus spp., Mycobacterium tuberculosis, rubeola virus (measles), and varicella-zoster virus (chickenpox).
22. Gathany, James. "This 2009 photograph captured a sneeze in progress, revealing the plume of salivary droplets as they are expelled in a large cone-shaped array from this man’s open mouth, thereby, dramatically illustrating the reason one needs to cover his/her mouth when coughing, or sneezing, in order to protect others from germ exposure." CDC.gov, 2009, https://phil.cdc.gov/details.aspx?pid=11161
