Changes in agent variability and time course of disease incidence during a year (as exemplified by dysentery)

The vulnerability of epidemic process during the period of minimum annual incidence of the disease is validated. Biological properties ofShigella sonnei are studied and their variability examined using the index for evaluation of the mean number of variations for a sign. Minimum agent heterogeneity coincides with minimum incidence of disease and maximum heterogeneity with its seasonal rises.