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WHAT ON EARTH ARE WE BREATHING AND ARE WE PROTECTED? AEROSOL ANALYSIS AND THE MASKS WE USE

Presentation Number: Su008

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AuthorBlock: David L. Carr-Locke1
1Medicine, Well Cornell Medical College, Brooklyn, New York, United States;

Abstract Body
Background: Transmission pathways for SARS-CoV-2 in humans include inhalation of virus-laden droplets (large >60µm, small 10-60µm), droplet nuclei (5-10µm) and aerosols (<5µm). The current pandemic has created a unique risk environment for gastrointestinal endoscopy. Universal Precautions mandates personal protective equipment appropriate for all patients assumed to be potentially infected. Protection of the airway of endoscopy personnel has become a dominant strategy requiring respirator-type masks. Protection in the community requires a different strategy. In the absence of accurate data regarding aerosolization during endoscopy, confirmation is needed concerning the degree of protection provided by masks worn by patients and staff. Masks have two functions: (1) to prevent the dissemination of droplets/aerosols from the mask-wearer to others and (2) to prevent the inhalation of droplets/aerosols by the mask-wearer.
Aims: To quantify particle concentrations that are transmitted through different mask types and thereby understand their blocking efficacy.
Methods: Using an Electrical Low Pressure Impactor (ELPI®, Dekati, Finland), aerosols were measured from breathing and that generated by a nebulizer. Bidirectional transmission of particles through masks was measured. The ELPI is able to separate particles into 14 diameters from 0.01 to 10 micrometers (µm) and quantify their concentration in real-time.
Results: Breathing produced particle concentrations ranging from 7.0/cm3 (diameters 7-10µm) to 130,000/cm3 (diameters 0.01-0.02µm). Cloth masks effectively blocked transmission of exhaled particles of 0.76µm and larger, whereas surgical and N95 masks blocked transmission across all particle sizes (with some exceptions). Nebulized saccharin 0.83% w/v (FT-11 solution) produced particles in a range from 2,000/cm3 (7-10µm) to 14,500,000/cm3 (diameters 0.01-0.02µm). Transmission of aerosols through cotton cloth, synthetic fabric, surgical and N95 masks tested from the wearer side was effectively blocked at all particle diameters whereas transmission from the outer (front) side of masks was completely effective at all particle diameters only for respirator masks (N95 and KN95). Surgical masks blocked transmission of particle diameters to the wearer at and above 0.4µm but non-medical masks were variable and some were improved by adding an integrated filter layer.
Conclusions: ELPI allows accurate real-time measurement of natural and artificial aerosol concentrations providing a valuable tool for assessing aerosol generation and mask transmission. This study has shown a high degree of airway protection to and from medical personnel using surgical and respirator masks. Community wearing of non-medical masks protects against shedding of aerosols by the wearer but the quality of inhalation protection is variable and non-standardized.