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Particle Size Distributions of Infectious Aerosols: Implications for Preventing Transmission
KEVIN FENNELLY, NIH/NHLBI
Abstract Number: 454
Working Group: Infectious Aerosols in the Age of COVID-19
Abstract
The current pandemic of coronavirus disease 2019 (COVID-19) has intensified interest once again in the transmission of respiratory pathogens. Such interest has vacillated since the outbreaks of multidrug resistant tuberculosis (MDR-TB) in the 1980s and 1990s, the Severe Acute Respiratory Syndrome coronavirus (SARS-CoV-1) pandemic of 2003, the H1N1 influenza pandemic of 2009, and the Middle East Respiratory Syndrome coronavirus (MERS-CoV) epidemic since 2012. I reviewed the research literature from the past twenty years on direct patient sampling of respiratory pathogens from cough aerosols and exhaled breath. Aerosols from both exhaled breath and cough aerosols are log normally distributed, suggesting that those producing the most infectious aerosol may be ‘super-spreaders.’ All pathogens were found predominately in small particle aerosols (< 5 microns mass median aerodynamic) diameter, and less so in larger aerosol particles. No pathogens were found only in large particle aerosols (> 5 microns). Over the past twenty years, infection control guidelines have used transmission within close proximity as a marker of exposure to large particle aerosols. This logic is fallacious, as humans expel polydisperse aerosols containing a mixture of both small and large particles. These data suggest that health care workers and others in close contact to persons with respiratory infectious diseases that are novel or potentially lethal should be protected by the use of N95 respirators at a minimum, as well as by engineering and administrative control measures currently used for airborne transmission. (These data have been published in Lancet Respiratory Medicine 2020.)