Objective  To explore a simple and reliable model for the prediction of incidence rate and trend of scarlet fever epidemic based on the seasonal regularity in prevalence of the disease.

  Methods  We collected data on monthly incidence of scarlet fever in 27 province-level regions across China between 2010 and 2017 via China Disease Prevention and Control Information System and analyzed the data for theoretic verification of winter-spring phenomenon in scarlet fever epidemics and to construct a model for the predication of the scarlet fever epidemic based on the winter-spring phenomenon theory.

  Results  The coincidence rate was 97.53% between the predicted peak scarlet fever incidence rates and the 162 observed rates in spring season in province-level regions during the period. For the province-level regional data, the difference (expressed as Y in prediction formula) in the peak incidence rate between two spring season epidemics of consecutive years were correlated positively with that (expressed as X) in the peak incidence rate between two winter season epidemics, with the correlation coefficients ranging from 0.21 to 0.98; moderate positive correlation (r > 0.5) between the Y and the X mentioned above was observed for 85.19% (23 of 27 provinces) of the data and high positive correlation (r > 0.8) was observed for 59.26% (16 of 27 provinces) of the data. Statistically significant regression models were established for 66.67% (18 of 27 provinces) of the data (all P < 0.05), with the correlation coefficients of from 0.81 to 0.98. A formula for predicting the incidence rate of scarlet fever in province-level regions was constructed: Y = 0.045 + 1.014X.

  Conclusion  Typical winter-spring phenomenon exists in the prevalence of scarlet fever in China.