“…Throughout this paper, we always assume that lim S→0 g(S, I)/S exists for all I ≥ 0, g (S, 0) lim I→0 g(S, I)/I > 0 for all S > 0, and g(S, I)/I is monotone nonincreasing with respect to I ∈ (0, ∞) for S ∈ (0, ∞). Obviously, the function g includes some special incidence rates [10,11,15,17,25,26,40,41], such as bilinear incidence rate g(S, I) = SI, saturation incidence rate g(S, I) = SI/(1 + mI) with a positive constant m denoting the half-saturation constant, Holling type II incidence rate g(S, I) = SI/(1 + mS), Beddington-DeAngelis incidence rate g(S, I) = SI/(aS + bI + c) with positive constants a, b, and c, and some other kinds of incidence rates like g(S, I) = e −mI SI and g(S, I) = SI/(1 + mI θ ) with positive constants m and θ (see, for example [8,30,36]). In [8], model (1) with bilinear incidence rate always has a globally asymptotically stable disease-free equilibrium E 0 and so the disease disappears if the basic reproduction number R 0 = Λβ µ(µ+α+λ) ≤ 1.…”