Study on the epidemiological characteristics and incidence trend of scarlet fever in Shanghai, 2005-2012

Abstract

To systemically analyze the epidemiological characteristics, molecular markers of circulating group A Streptococcus (GAS) isolates and the incidence trend of scarlet fever in Shanghai from 2005 to 2012 as well as to explore the practice of GAS isolates surveillance program and the combined mathematical model in the early warning of scarlet fever. The morbidity series of scarlet fever were retrieved to analyze and fit the combined mathematical model which comprised an autoregressive integrated moving average (ARIMA) model and a neural network. GAS isolates surveillances programs were implemented on community healthy population, using the emm typing and superantigens detecting method in Shanghai during the epidemic period of scarlet fever in 2008, 2010 and 2012. The standardized prevalence of GAS isolates was estimated with the demographic data. From 2005 to 2012, there were a total of 9410 scarlet fever cases reported in Shanghai including local registered residents and immigrant population, showing that the distribution of patients as sporadic. The morbidity kept rising with seasonal and periodical variations and the peak was in 2011. The average morbidity was 6.012 per 100 000 persons. Morbidity in the the suburban was significantly higher than that in the urban areas. Children at 4 to 8 years old were easy to be involved. The mean error rate of single ARIMA model,ARIMA-GRNN and back propagation artificial neural network combined model were 0.268, 0.432 and 0.131 respectively. The predicted incidence of scarlet fever in 2013 would keep fluctuating within a narrow range from 0.446 to 3.467 per 100 000 persons. A total number of 4409 throat swab samples were collected through the GAS isolates surveillance programs in 2008, 2010 and 2012. The standardized prevalence of GAS isolates in each year were 0.000%, 0.000% and 1.092%. 18 GAS isolates were identified and 15 isolates (83.33%)belonged to emm 12.0. The morbidity of scarlet fever would continue to maintain an upward trend in Shanghai and the techniques used in GAS isolates surveillance program and in the combined mathematical model could be applied for the early warning system on scarlet fever.