Etiological analysis of influenza surveillance data in Yangzhou from 2012 to 2017

Objective To find out the characteristics and regularity trend of influenza activity according to the analyses of influenza surveillance data in Yangzhou from 2012 to 2017, and to provide scientific supports for predicting and controlling the pandemic outbreak of influenza effectively. Methods The influenza samples were collected from Northern Jiangsu People′s Hospital, Yangzhou First People's Hospital and Gaoyou People’s Hospital, using fluorescent RT-PCR method to detect influenza virus nucleic acid and classifying influenza virus subtypes. Finally, the surveillance data from January, 2012 to December, 2017 of influenza like illness (ILI) cases of Yangzhou were analyzed. Results Totally 18 083 throat swabs of ILI specimens were collected from 2012—2017 in Yangzhou, 1 983 samples were positive (10.97%), the difference in positive rates of adjacent years was statistically significant (χ2=167.93, P<0.001). In Yangzhou city, influenza virus kept activative in whole year. The influenza epidemic season was winter-spring and summer, accounting for 83.61% of all positive cases, with type A influenza prevalent throughout all year and type B influenza mainly prevalent in spring and winter, each subtype showed alternating prevalence. The influenza virus infection occurred in every age group. The highest positive rate was 16.33% in the age group of 10-19 years and the lowest was 8.52% in the age group of 20-29 years among all detected age groups. Conclusions From 2012 to 2017, the epidemic of influenza in Yangzhou was obviously seasonal and all the subtypes of influenza were in prevalent status alternately. The high-risk groups of Influenza were infants and teenagers who under the age of 19 years. So a long-term influenza surveillance is much needed for the early warning and forecasting the spread of influenza. Key words: Influenza; Etiology; Surveillance