Experimental Tracing and Modeling of Exogenous Microbe Dynamics in Home Environments

Particles such as allergens and pathogens can invade indoor environments via human activities, affecting occupant health and indoor microbiota. However, the particle transmission dynamics and distribution patterns remain underexplored. In this study, Lactobacillus strains were applied as tracers to the palms and shirtfronts of adults in four families, whereafter they were dispersed into the residential environments overnight through routine activities. The target genes of the tracers were detected in over 80% of the extracted surface samples. While touch events and contamination were both concentrated on specific surfaces, frequent touching did not correspond to high contamination. Instead, contamination levels were affected by a combination of factors, including the sequence of surface touches and the promptness of handwashing. Additionally, resuspension redistributed tracers more uniformly across surfaces, with tracer concentrations on air-conditioning filters being twice the median value for all environmental samples. Accordingly, we established a physical model that predicts tracer distribution considering surface touch and resuspension. Based on the modeling results, hand-seeded and shirt-seeded contaminants were reduced more effectively through prompt handwashing and shirt changing upon entering home than by cleaning multiple surfaces at a later time. These findings provide insights into the dynamic processes underlying indoor infection, hygiene, and microbiota.