Microbial particle transfer via surface touch

Abstract

Infectious diseases can spread by means of fomites, i.e., contaminated inanimate objects. Infectious bacteria or viruses are deposited on environmental surfaces mostly through human activities, such as when a pathogen carrier (e.g., an infected individual) touches a surface or deposits pathogen-containing aerosols on a surface. The microbes remaining on a fomite can be transferred to and infect anyone who touches them. A single touch of a contaminated fomite can transfer a fraction of the surface microbes to the hands of the recipient. The issue of microbial transfer has thus attracted great concern in fields such as food harvest and preparation, nosocomial infection, and public hygiene. In this study, a preliminary understanding of microbial transfer during surface touch was reached by reviewing studies that tested in detail surface touch and the ensuing microbial transfer rate. The factors that affect microbial transfer were analyzed. A model was established to evaluate the rate of microbial transfer during surface touch. Among the numerous physical factors involved were the touch force, surface roughness, particle size, and existence of rub. The microbial transfer rate was also calculated for repeated touch between a pair of surfaces and for sequential touch between a microbial donor surface and a series of recipient surfaces. Experiments were carried out to validate the new model. Bacteria, phage, and yeast were used as the model microbes to perform the transfer experiment by surface touch. A specially made touching machine was used to control the surface touch. As the experiment made clear, the effect of the factors involved in the model were well evaluated by the new model. However, the large deviation of the transfer rate in the tests indicated that the model did not include some important factors that significantly influence microbial transfer. Based on the new model, it was established that the microbial particles between a pair of surfaces could reach an equilibrium after sufficient contacts between the surfaces. Assuming that more than two types of surfaces form a surface network, it was asked whether an equilibrium still existed as an ultimate distribution of the particles. Experiments were carried out using the touching machine. Fluorescent particles were used as a surrogate of the microbes. For the five types of surface in the experiment, the particle distribution among the surfaces was very close to a stable state, which is considered to be an equilibrium, although particle numbers among surfaces could theoretically fluctuate indefinitely. Based on the new model, a new method to evaluate the bacterial transfer rate from finger to surface was applied. Sequential touch was performed between a finger as the bacterial donor and a series of clean glass surfaces as the recipients, and the bacteria transferred to the surfaces were cultured in situ. The new method considerably increased the accuracy of evaluating the transfer rate while reducing the workload.