Characteristics of multiple infections of influenza in Beijing during 2017–2020 influenza seasons

  Objective  To analyze the proportion and epidemiological characteristics of multiple infections of influenza in Beijing during 2017−2020 influenza seasons.

  Methods  The composition and distribution of multiple infection cases were analyzed by using the surveillance data of influenza in Beijing from 2017 to 2020.

  Results  During 2017−2020 influenza seasons, 18637 multiple infections were reported (accounting for 4.13%), and the proportion of multiple infections in a single influenza season ranged from 0.10% to 0.93%. The trend of multiple infection cases was consistent with the change of the total number of influenza. There were five peaks of reinfection on the 120^th, 285^th,375^th,450^th and 725^th day since the first infection. Univariate analysis found that there were significant differences in the proportion of multiple infections among gender, age groups, occupation and living districts. And the proportion of multiple infections was higher in male, 12 years old and below, nursery children, scattered children, healthcare providers and students, Chaoyang, Haidian, Changping, Xicheng and Tongzhou districts.

  Conclusion  There were many multiple influenza infections in Beijing, and great differences in multiple infections could be found at different times, regions and populations.