Objective To explore the epidemic levels and epidemiological characteristics of influenza-like illness (ILI) in Hongkou District of Shanghai, to track the trends in virus mutations, so as to offer a scientific foundation for precisely predicting influenza epidemic trends, providing early alerts, and implementing prompt prevention and control measures.

Methods Data on ILI and etiological surveillance from Hongkou District between 2015 and 2024 were collected and statistically analyzed.

Results The consultation percentage of ILI (ILI%) in Hongkou District from 2015 to 2024 was 0.58%, and the differences were statistically significant between different years (χ²=19 280.500, P<0.001), with winter and summer being the prevalence peaks. The highest proportion of ILI cases was observed in the 25‒<60 years age group, and the proportion of cases aged ≥60 years showed an increasing trend. The positive rate for influenza viruses was 17.60%, with seasonal influenza A (H3N2) subtype (49.78%) and influenza A(H1N1) (30.03%) being the predominant strains,and the positive rate was different by years. There was a correlation between ILI% and the positive rate of influenza viruses (r=0.260, P<0.001). The median intensity of influenza activity in 2023‒2024 was 23.09, which was significantly higher than that in 2015‒2019 (H=37.052, P<0.001) and that in 2020‒2022 (H=40.436, P<0.001).

Conclusion From 2015 to 2022, the ILI% in Hongkou District, Shanghai remained at a relatively low level, but it significantly increased in 2023‒2024, with peaks observed in winter and summer. The predominant influenza virus strains varied and alternated by years. The 2023‒2024 period witnessed an intensified influenza activity. It is necessary to continuously monitor the impact of other respiratory pathogens on influenza epidemic, so as to provide a scientific basis for early warning and prevention and control of influenza.