The phase state of respiratory particles and growth medium, which is regulated by relative humidity (RH), has been linked to the survival of pathogens in aerosol particles and deposited on surfaces. Previous studies suggest that the relationship between RH and pathogenic viability follows a U-shaped pattern, and further propose that NaCl efflorescence influences the recovery of virus viability at intermediate RH. However, the exact mechanism for viral inactivation is not well-understood. Here, we aim to study the conditions relevant to disease transmission and viral inactivation. We study the phase changes of levitated aerosol particles composed of model respiratory compounds (salt, protein), culture media, and artificial saliva with decreasing RH. We observe humidity-dependent amorphous (semi-) solid-phase transitions at intermediate RH in which organic components become more viscous with decreasing RH. Efflorescence of the inorganic fraction was often suppressed or inhibited entirely. These humidity-dependent phase states were not significantly altered by the presence of viral material. Therefore, we propose an additional factor that may explain the U-shaped RH-dependent virus viability; we hypothesize that organic and protein-rich compositions have a protective effect on pathogens through the formation of viscous phase states that hinder the diffusion of disinfectants. The increase in viscosity of the amorphous phase states at intermediate to low RH offsets the increase in solute concentration by hindering disinfection reactions. We discuss the implications for amorphous phase states of respiratory aerosol for disease transmission under certain conditions and provide a conceptual framework toward predicting the survival of pathogens in varying suspension media and ambient conditions.<br/>.

Influence of phase state and relative humidity on the survival of pathogens in aerosol particles

ACS Spring 2022

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