Weather-related changes in the dehydration of respiratory droplets on surfaces bolster bacterial endurance

Abstract

AbstractHypothesisThe study shows for the first time a fivefold difference in the survivability of the bacteriumPseudomonas Aeruginosa(PA) in a realistic respiratory fluid droplet on fomites undergoing drying at different environmental conditions. For instance, in 2023, the annual average relative humidity (RH) in London (UK) is 71%, whereas in Delhi (India), it is 45%, showing that disease spread from fomites could have a demographic dependence. Respiratory fluid droplet ejections containing pathogens on inanimate surfaces are crucial in disease spread, especially in nosocomial settings. However, the interplay between evaporation dynamics, internal fluid flow and precipitation and their collective influence on the distribution and survivability of pathogens at different environmental conditions are less known.ExperimentsShadowgraphy imaging is employed to study evaporation, and optical microscopy imaging is used for precipitation dynamics. Micro-particle image velocimetry (MicroPIV) measurements reveal the internal flow dynamics. Confocal imaging of fluorescently labelled PA elucidates the bacterial distribution within the deposits.FindingsThe study finds that the evaporation rate is drastically impeded during drying at elevated solutal concentrations, particularly at high RH conditions. MicroPIV shows reduced internal flow under high RH conditions. Evaporation rate influences crystal growth, with delayed efflorescence and extending crystallisation times. PA forms denser peripheral arrangements under high evaporation rates and shows a fivefold increase in survivability under low evaporation rates. These findings highlight the critical impact of environmental conditions on pathogen persistence and disease spread from inanimate surfaces.Graphical abstract