Etiological analysis of influenza-like cases in Taizhou City， Zhejiang Province from 2013 to 2022

Objective To analyze the etiological results of influenza-like case surveillance in Taizhou， Zhejiang Province from 2013 to 2022， to timely understand the epidemic trend of influenza viruses and the change rule of dominant virus strains， and to provide reference for the prevention and control of influenza in this region.

Methods Influenza virus nucleic acid was detected by real-time PCR in 24 183 influenza-like cases.

Results The positive rate of influenza virus in 24 183 samples was 18.43%， the highest positive type was seasonal H3 （37.34%）. There was no a significant difference in positive rate between different genders （χ²=0.148， P=0.701）. There was significant difference in the positive rate among different age groups （χ²=496.626， P<0.001）， and the highest positive rate was found in the 25‒59 age group （22.56%）. The positive rate in different years was statistically significant （χ²=1 670.922， P<0.001）. The positive rate from 2013 to 2019 showed an upward trend （χ²=30.559， P<0.001）. The lowest positive rate was in 2020 （0.04%）， and the positive rate from 2021 to 2022 showed an upward trend （χ²=304.465， P<0.001）. The dominant strains were different in different monitoring years. There was a significant difference in the positive rate of influenza in different months （χ²=1 652.455， P<0.001）， and the peak of influenza was mainly concentrated in December‒March and July‒August.

Conclusion From 2013 to 2022， the positive rate of influenza virus in Taizhou showed a wavy dynamic change， and the dominant strains were different in different years， presenting alternate epidemic characteristics. It is necessary to strengthen the etiological surveillance of influenza virus and improve the prevention and control measures with influenza vaccine.