High-touch surfaces with moderate contamination levels as key nodes in microbial dissemination

Hand-touching of contaminated surfaces is an established mode of infection transmission. However, the role of touch-mediated pathogen spread remains debatable, as frequently touched surfaces may exhibit low pathogen loads. To inform disease-prevention protocols, this study experimentally and theoretically investigated contamination in surface-touch networks as a function of touch behaviours and pathogen sources. Observation of four settings containing bacterial tracer particles showed that while most surfaces were rarely hand-touched, networks were formed by several high-touch 'hubs'. Counterintuitively, heavy contamination was primarily exhibited by some rarely touched surfaces. A new model for simulating contaminant spread via surface touch was developed and validated using the experimental data. The simulation revealed that surface contaminants were typically distributed non-uniformly. In scenarios with one or several localised contaminant sources, high-touch surfaces typically exhibited moderate contamination. A network with a high density of touches or multiple contaminant sources exhibited accelerated spread to a uniform contaminant distribution, with high-touch surfaces quickly approaching moderate concentrations. Therefore, surface touching could either contaminate or 'clean' surfaces. Undetectable or low pathogen concentrations on high-touch surfaces should not be interpreted as an absence of contaminated surfaces or of pathogen spread via surface touch.