Analytic justification for CD-susceptibility.

The ability of CD to invade the three uninfected steady states , , and depends upon the sign of : a positive value indicates a CD-susceptiblity, while a negative value indicates CD-resilience. This result follows from analysis of Eq (1).CD入侵三个未感染稳态（、和）的能力取决于的符号：当取值为正时，代表CD易感性；取值为负时，则代表CD抗入侵性。该结论可通过对公式(1)的分析推导得出。