The dynamics of the pathogen’s biological properties, infection conditions, and the biological state of the host organism determine the constant evolution of clinical manifestations and outcomes of infectious diseases (Pokrovsky V.I. et al., 2003). The previously held view of dysentery as a disease with a mild course and decreasing lethality, prevalent by the mid-1980s, was revised due to a sharp worsening during the epidemic spread of Shigella flexneri 2a in the 1990s (Solodovnikov Yu.P., 1992; Kartsev A.D., 1992; Pokrovsky V.I., Yushchuk N.D., 1994; Belyaeva T.V., 1995, 2003; Kondrasheva L.N. et al., 2003). Literature analysis indicates that Shigella dysentery caused by Flexner bacilli in recent years has been marked by an increased proportion of severe cases and unfavorable outcomes (Brodov L.E. et al., 1996; Rakhmanova A.G. et al., 1996).