Epidemiologic and etiological characteristics of influenza in Baoshan district of Shanghai, 2018−2020

  Objective  To describe the epidemiological characteristics of influenza in Baoshan district of Shanghai from 2018 to 2020, and provide a strong scientific basis for the local prevention and control of influenza.

  Methods  The incidence data and the etiological surveillance data of influenza-like illness (ILI) in Baoshan from 2018 to 2020 were systematically analyzed.

  Results  In 2018 and 2019, the incidence of ILI was higher in winter and spring, and was stable in summer and autumn in Baoshan. Compared with 2018 and 2019, The proportion of ILI in 2020 increased significantly (χ²=1340, P＜0.01), and reached the peak on January 23, 2020. The ILI proportion increased significantly in spring, summer and autumn. The highest ILI proportion was found in young and middle-aged people aged 25−59 years, followed by children aged 0−15 years. A total of 3141 samples of ILI cases were detected from 2018 to 2020, and 497 were positive for influenza virus with the positive rate of 15.82%. The positive rate was highest in 2019 (29.51%) and lowest in 2020 (5.00%) (χ²=241.18, P<0.01). Influenza A (H1N1) virus was predominant in 2018 (7.92%), influenza A (H3N2) virus was predominant in 2019 (11.77%), and influenza B virus was predominant in 2020 (3.39%).

  Conclusion  The influenza activity in Baoshan was stable during 2018−2019, and the ILI proportion increased significantly in the early stage of COVID-19 outbreak in 2020, but the positive rate in the detection of ILI cases’ samples in the whole year of 2020 was very low.