Fig. 3

Seasonal distribution of bacillary dysentery cases in China, 2004–2014. a The frequency distribution of bacillary dysentery cases by month of illness onset. b The seasonal index of bacillary dysentery. The seasonal index was calculated by month as the average case count for a given month divided by the average monthly case count during the entire 11-year time period, 2004–2014. No obvious seasonal pattern was expected if the seasonal index of each month was close to 1.0