Abstract:
Objective To understand the epidemiological and etiological characteristics of influenza-like illness (ILI) in Tongzhou district, Beijing, from 2021 to 2024, and provide evidence for the prevention and control of infectious diseases.
Methods The epidemiological and etiological surveillance results of ILI in Tongzhou from 2021 to 2024 were collected from the infectious disease surveillance and early-warning information system of hospitals in Beijing. The data were processed by using Excel 2021. Descriptive analysis on the epidemiological and etiological characteristics of ILI was conducted by using software R 4.4.2. A Pearson correlation analysis was performed to explore the relationship between the ILI percentage (ILI%) and the positive rate of pathogen detection.
Results The proportion of ILI cases to the total number of outpatient and emergency cases increased year by year in Tongzhou from 2021 to 2024, especially during 2023 - 2024 with multiple distinct peaks. The circulating strains of influenza viruses varied in different years. From 2021 to 2024, the annual predominant subtypes included "B, A(H3N2)/A(H1N1), A(H3N2)/B and A(H1N1)", and no B Yamagata lineage strain was detected. The distribution of ILI cases varied in different age groups. The age groups 25~<60 years and 5~<15 years were the main populations affected by ILI. The number of ILI cases in age group 5~<15 years increased significantly from 2023 to 2024. The positive rate of influenza virus increased year by year from 2021 to 2023 and then decreased significantly in 2024. The positive rate of SARS-CoV-2 declined during 2023 - 2024. The positive rate of influenza virus detection was consistently positively correlated with the ILI% from 2021 to 2024 (P<0.05).
Conclusion In recent years, the ILI% changed significantly in Tongzhou, with children aged 5~<15 being the key population in influenza prevention and control. Influenza virus has crucial impact on ILI%. The inconsistency between the ILI% and the pathogen positive rate suggested the possible existence of other respiratory pathogens. It is essential to pay attention to the changes of ILI pathogens and conduct active surveillance for multi-pathogens causing respiratory tract infection.