[Demonstration on Z-D phenomenon in the occurrence of infectious diseases].

A systematic analysis, including retrospective test by means of correlation analysis and extrapolation test was carried out to demonstrate a new hypothesis named Z-D phenomenon which states that the skew of a seasonal case distribution curve of an infectious disease may appear to be the omen of its epidemic trend in the following year. A total number of 353 data sets belong to 17 notifiable infectious diseases in 29 provinces and the whole nation were chosen. Data from retrospective test showed that 91.2% (322/353) of the correlation coefficients of between the skew of the seasonal distribution curve of the previous year and the morbidity variation of its following year were negative. The extrapolation test showed that 68.1% (203/295) of the data sets accorded with the actually epidemic situation at the level of r < -0.5. The results proved the existence of Z-D phenomenon may serve as an indicator for the purpose of forecasting. Using this systematic analysis, we found that Z-D phenomenon was more expressive in viral hepatitis, pertussis, epidemic cerebrospinal meningitis and scarlet fever than in other diseases.