Rise of measles morbidity in Pudong New Area of Shanghai: Its influence on the seasonal prevalence of measles

Objective To investigate the seasonal prevalence of measles from 1996 to 2008 in Pudong New Area of Shanghai. Methods Circular distribution method was used to compare and analyze the situations on the peak day and in the peak duration of measles morbidity at periods of different morbidity levels. Results The peak days of the 6 prevalence periods were April 18, May 11, September 18, May 17, April 9 and May 19, with the peak duration being 120 days, 129 days, 194 days, 136 days, 100 days and 163 days, respectively.The peaks of measles prevalence concentrated in April and May. Conclusion Rise of measles morbidity cannot change its seasonal prevalence or peak time.Simple calculation and intuitive description have advantages of circular distribution method in analyzing the seasonal variation of diseases with single peak and cyclic change.