Analyses of pathogen spectrum and epidemiological characteristics of respiratory viruses in adult influenza-like illness cases in Putuo District of Shanghai from 2015 to 2024

Objective To analyze the composition of respiratory virus pathogen spectrum and epidemiological characteristics among adult influenza-like illness (ILI) cases in Putuo District of Shanghai from 2015 to 2024, summarize the epidemic patterns of respiratory viruses across different time periods and populations, and provide scientific evidence for the prevention and control of adult respiratory virus infections in Putuo District of Shanghai. Methods This study retrospectively collected surveillance data of 2 273 adult ILI cases from sentinel hospitals under the comprehensive surveillance system for acute respiratory infections in Putuo District of Shanghai from 2015 to 2024. Descriptive epidemiological methods were adopted to analyze the temporal and population distribution characteristics of respiratory viruses including influenza virus (IFV), respiratory syncytial virus (RSV), adenovirus (ADV), human metapneumovirus (HMPV). The mixed infection status among different age groups was compared, and the distribution of influenza virus subtypes was described. SPSS 22.0 and WPS Office software were used for statistical analyses. Results The overall detection rate of respiratory viruses in 2 273 adult ILI cases was 43.51%. The detection rate in females (45.48%) was significantly higher than that in males (41.25%), with statistical significance (X²=4.113, P=0.043). The population aged 60 years old and above had the highest detection rate (47.41%) (X²=8.430, P=0.014). The detection rates in winter (50.41%) and summer (48.42%) were higher than those in other seasons (X²=47.028, P<0.001). The overall viral detection rate decreased after 2020 (X²=208.411, P<0.001). The detection rates of various viruses varied by year, in that IFV and ADV had high detection rates from 2015 to 2019 (all P<0.001), while human coronavirus (HCoV) and rhinovirus/enterovirus (HRV/EV) exhibited higher detection rates from 2020 to 2022 (all P<0.001). Co-infection of IFV with HCoV was the most common, followed by co-infection of IFV and ADV, together accounting for 50.00% of all mixed infections. During the surveillance period, the detection rate of IFV was remarkably higher than that of other respiratory viruses. Influenza B/Victoria lineage predominated in 2021, followed by successive predominance of influenza A(H1N1), A(H3N2), and co-circulation of the two subtypes from 2022 to 2023. Influenza A(H1N1) re-emerged as the predominant subtype in the first half of 2024. Conclusion From 2015 to 2024, adult respiratory virus infections mainly prevailed in winter and summer, and people aged 60 years old and above were the key high-risk population. The detection rates of respiratory viruses declined after 2020. IFV was the predominant pathogen detected, and different influenza virus subtypes circulated alternately each year.