Epidemiological characteristics of influenza infection in visiting patients from 2019 to 2023

Objective To describe and analyze the epidemiological characteristics of influenza infection in outpatients, emergency patients, and inpatients in a tertiary TCM hospital，and to provide evidence-based basis for formulating prevention and control measures of respiratory tract nosocomial infections.Method The Influenza Virus (IFV) nucleic acid test results of outpatients, emergency, and hospitalized patients in a tertiary TCM hospital from Jan.2019 to Sep. 2023 were collected, of which the epidemical distribution was described and the difference was compared by chi-square test, Kruskal-Wallis test and Run test.Result 7442 outpatients, emergency patients, and inpatients were included in the study, and the total positive rates was 23.58%。Compared to 2019（16.96%）, test positive rates of IFV decreased during 2020-2022（1.99%-5.88%）, then it resurged and went beyond historical levels during Jan.-Sep. 2023（39.08%）.The incidence peaks occurred in winter in 2019（Z=-5.669,P＜0.001）and 2023（Z=-4.740,P＜0.001）,and were suppressed during 2020-2022.The positive rates were highest in age groups ≥60 years（37.74%-70.83%）,and in hospitalized patients（45.28%-83.33%）from 2019 to 2022. During Jan. to Sep. 2023 the proportion of infections in age groups 25~59 years（50.07%）and in outpatients, emergency patients（91.51%）increased. IFV was mainly isolated among hospitalized patients in respiratory, nephrology and orthopedic ward, and among outpatients in fever clinic, pediatric and respiratory clinic. Influenza A（55.17%-99.75%）was mainly detected during 2019-2021, 2023,while influenza B（60.00%）in 2022.Conclusion The trend of IFV positive rates in hospital was almost equal to the local epidemiological characteristics of influenza infection, which was also influenced by public health policy and features of patients. Strategies and measures for the prevention and control of respiratory tract nosocomial infections should be formulated based on the season, age, department distribution, and pathogenic characteristics of influenza infection among patients.