A coupled hand and surface hygiene criterion on heterogeneous surface touch networks.

Contaminated hands of people and contaminated surfaces of inanimate objects (fomites) can spread microbes that cause enteric and respiratory infections. Thus, hand hygiene and surface hygiene are probably the most widely adopted public health interventions for controlling such infections. However, conclusions of studies on the effectiveness of these interventions are often inconsistent, likely because such studies have examined these interventions separately and thus not detected their interactions, leading to differing conclusions about their individual impact. In this study, it is proposed that hand and environmental surface hygiene (including disinfection) should be coupled to control contamination spread between surfaces, especially within heterogeneous surface touch networks. In these networks, surfaces and individuals have varying contact frequencies and patterns, reflecting the diverse and non-uniform interactions that typically occur in real-world environments. Accordingly, we propose a new theoretical framework to delineate the relationships between hand hygiene and surface hygiene. In addition, the performance of a model based on this framework that used real-world behavioural data from a graduate student office is reported. Moreover, a coupled hygiene criterion for heterogeneous networks is derived. This criterion stipulates that the product of the pathogen-removal rates for hands and surfaces must exceed a cleaning threshold to ensure the exponential decay of contamination. Failure to meet this threshold results in a non-zero steady prevalence of contamination. Furthermore, the cleaning threshold increases as the numbers of surfaces and hands increase, highlighting the significant impact of network structures on hygiene practices. Thus, extensive cleaning may be necessary in crowded indoor environments with many surfaces and occupants, such as cruise ships, to prevent super-large outbreaks of, for example, noroviral infections. Overall, the findings of this study reveal how improved and integrated hygiene control can prevent fomite transmission.