In this paper, we study a type of susceptible-exposed-infected (SEI) epidemic model with varying population size and introduce the random perturbation of the constant contact rate into the SEI epidemic model due to the
universal existence of fluctuations. Under some moderate conditions, the density of the exposed and the infected individuals exponentially approaches zero
almost surely are derived. Furthermore, the stochastic SEI epidemic model
admits a stationary distribution around the endemic equilibrium, and the solution is ergodic. Some numerical simulations are carried out to demonstrate
the efficiency of the main results.