Incidence trend and epidemiological characteristics of scarlet fever in Zibo City from 1956 to 2014

Objective To analyze the incidence trends and epidemic characteristics of scarlet fever in Zibo City from 1956 to 2014, to investigate the emm genotype of group A streptococcus(GAS) in Zibo from 2013 to 2014, and to provide evidence for preventing and controlling scarlet fever. Methods Descriptive statistical analysis was performed on epidemiological data of scarlet fever during 1954-2014 obtained from historical epidemic data and Diseases Reporting Information System. GAS were isolated from throat swabs of the case from 2013 to 2014,polymerase chain reaction(PCR) was conducted to amplity the emm gene, and to determine the genotype of emm.Results A total of 13 470 cases and 24 death cases were reported in the whole city from 1956 to 2014, with the annual incidence rate between 0.51-70.47/100 000. The mortality rate was 0.18%. There were seven popular cycles during the 59 years with 5 to 10 years per cycle. The two peak stages occurred in spring(April-June) and winter(Nov.-Jan.) each year. The age of the cases were under 15 years old, accounted for 93.22% of the total cases. A total of 14 GAS strains were isolated during the recent 2 years, and there were 6 gene subtypes including 6 strains of emm 1.0, 1 strain of emm 1.24, 1 strain of emm 1.70, 4 strains of emm 12.0, 1 strain of emm 12.7 and 1 strain of emm 75.0. Conclusions The incidence rate of scarlet fever was decreasing during the 59 years, with obvious periodicity and seasonality incidence. Primary school students and kingdergarten children are the focus population for prevention and control the scarlet fever. The most epidemic genotype of GAS strains were emm 1.0 and emm 12.0 during 2013-2014 in Zibo City.