Analysis of children influenza surveillance results in Wenzhou from 2009 to 2014

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Objective To analyze the etiology and epidemiological characteristics of influenza in Wenzhou from 2009 to 2014, so as to provide the scientific basis for control and prevention of influenza. Methods Throat swab specimens of influenza like illness (ILI) were collected from national influenza surveillance sentinel hospitals for nucleic acid detection with real-time PCR and virus isolation, culture and sequencing, and the results were analyzed with statistical methods. Results During the 8 years, a total of 10 577 089 cases from outpatient and emergency department were monitored in sentinel hospitals. There were 337 896 ILI cases with an average ILI treatment rate of 3.19%. A total of 4 046 ILI samples were detected in children, 511 were positive for influenza, the positive rate was 12.63%. Among the detected influenza types, type B had the highest proportion, followed by H3N2. Among the 6 age groups, the number of flu patients was the highest in 0-3 years old group, the positive rate in 10-12 years old group was the highest (35.03%). There were 28 and 45 amino acid sequence mutations of HA fragment in influenza A and B, respectively, which included multiple mutation of 391 and 145 amino acids. The phylogenetic analysis showed that the strains of type B were different in different years, and Yamagata evolved into Y1 and Y2 two branches. Conclusions The prevalence peaks of influenza in children occurred in winter and spring in Wenzhou city, accompanied by small peaks in summer. Three subtypes of serotypes B, H3N2 and A(H1N1) dominated alternatively in Wenzhou during the 8 years. We should focus on strengthening the prevention and control of influenza in preschool children and primary and secondary school students. Key words: Influenza; Surveillance; Influenza virus; Children