After initializing the surfaces, people and behaviors, we applied a surface contamination model  to calculate the virus concentrations on different surfaces. The virus quantities on surfaces after one touching action only depend on the state before the action rather than the sequence of states that preceded it, which conforms to the definition of the Markov chain . Therefore, every behavior consisting of a series of touching actions can be regarded as a discrete-time Markov chain, while environmental surfaces and hand surfaces can be regarded as different states in the Markov chain. The surfaces of the mucous membranes are special surfaces so the exposure doses to the mucous membranes were calculated via the surface contamination model. Furthermore, a dose-response relationship model  was used to predict the infection risk.