Epidemiological and etiological surveillance for influenza-like illness in Huairou district, Beijing, 2014−2022

  Objective  To understand the epidemiological and etiological characteristics of influenza in Huairou district, Beijing, from 2014 to 2022, and provide scientific evidence for influenza prevention and control.

  Methods  Data of influenza-like illness (ILI) cases and etiological surveillance results in Huairou from 2014 to 2022 were collected for descriptive and statistical analyses.

  Results  From September 2014 to August 2022, a total of 49 716 cases of ILI were reported from two sentinel hospitals in Huairou, accounting for 0.35% of the total outpatient/emergency cases, and 17 156 pharyngeal swabs were collected from the ILI cases during the eight years, of which 3 091 were positive for influenza viruses, with a positive rate of 18.02%. The positive rate was highest in age group 25– years (20.21%). The peak of positive rate of influenza virus in all the surveillance years occurred during December-March, and the differences in the annual composition of influenza virus subtypes were significant (χ²=1785.065, P＜0.001), with the main subtypes of A (H3N2) and B Victoria lineage. The influenza virus positivity rate was significantly lower after 2020.

  Conclusion  Influenza mainly occurred in winter and spring in Huairou from 2014 to 2022, with different subtypes and different intensities. People in age group 25– years were the key population affected. Comprehensively preventive and control measures could also significantly reduce the incidence of influenza.