Unravelling the Dynamics of Bacterial-Laden Respiratory Droplets: Epidemiological Transfer from Fomites to Susceptible Host

This study provides the first comprehensive investigation into how pathogen-laden respiratory droplets transfer diseases via inanimate surfaces. Respiratory fluid ejections containing pathogens pose a significant health threat, especially in high-traffic areas like hospitals, public transport, restaurants, and schools. When these droplets dry on surfaces, they form deposits that can transfer pathogens to healthy individuals through contact and can be ingested via the oral or nasal route. The study examined the effects of varying salt and mucin concentrations in respiratory fluid droplets containing Pseudomonas aeruginosa (PA). Results showed that PA viability increased tenfold at elevated mucin concentrations, while changes in salt concentration had minimal impact. Adhesive properties of the deposits were analysed using atomic force spectroscopy and scotch tape test. Pathogen transfer from the deposit to a fingerprint patterned model thumb at different relative humidity (RH) levels was assessed using confocal microscopy, showing significant pathogen transfer at elevated RH. Out of 106 CFU/ml pathogens in deposits, 17% to 38% are potentially transferable, with most of the transfer occurring from the droplets edge deposits. The study also explored evaporation, internal flow, and precipitation dynamics, with deposit and pathogen distribution characterized by optical profilometry, scanning electron microscopy, and confocal microscopy.