Carbohydrate vitrification in aerosolized saliva is associated with the humidity-dependent infectious potential of airborne coronavirus


 An accepted murine analogue for the environmental behavior of human SARS coronaviruses was aerosolized in microdroplets of its culture media and saliva to observe the decay of its airborne infectious potential under relative humidity (RH) conditions relevant to conditioned indoor air. Contained in a dark, 10 m3 chamber maintained at 22 °C, Murine Hepatitis Virus (MHV) was entrained in artificial saliva particles that were aerosolized in size distributions that mimic SARS-CoV-2 virus expelled from infected humans’ respiration. As judged by quantitative PCR, more than 95% of the airborne Murine Hepatitis Virus aerosolized was recovered from microdroplets with mean aerodynamic diameters between 0.56 μm and 5.6 μm. As judged by its half-life, calculated from the median tissue culture infectious dose (TCID50), saliva was protective of airborne murine coronavirus through a relative humidity range recommended for conditioned indoor air (60% < relative humidity < 40%; average half-life = 60 minutes). However, its average half-life doubled to 120 minutes when relative humidity was maintained at 25%. Saliva microaerosol was dominated by carbohydrates, which presented hallmarks of vitrification without efflorescence at low relative humidity. These results suggest that dehydrating carbohydrates can affect the infectious potential coronaviruses exhibit while airborne, significantly extending their persistence under the drier humidity conditions encountered indoors.