Abstract：Objective To investigate the epidemiological characteristics of influenza in Nanchong City, Sichuan Province from 2016 to 2025, so as to provide references for formulating targeted influenza prevention and control strategies. Methods Data on confirmed and clinically diagnosed influenza cases with current residence in Nanchong City reported from January 1, 2016 to December 31, 2025 were extracted from the Chinese Disease Prevention and Control Information System. The number of influenza-like illness (ILI) visits and etiological monitoring data from sentinel hospitals in Nanchong City during the same period were collected through the Chinese National Influenza Surveillance Information System. Descriptive analysis was conducted to clarify the population, temporal and regional distribution of influenza cases as well as etiological results of ILI. The average annual percent change (AAPC) was used to analyze the trend of reported influenza incidence. Seasonal index (SI) was used to identify seasonal epidemic characteristics, and spatial autocorrelation analysis was used to explore the spatiotemporal distribution of influenza incidence. Results A total of 133 861 influenza cases were reported in Nanchong City from 2016 to 2025, with an average annual reported incidence of 240.30/105, showing a rising trend (AAPC=82.765%, P<0.05). The periods from January to March and November to December were the peak epidemic seasons with SI values over 100%. The average annual reported incidence was higher in males than in females (P<0.05). The age groups of 0-<15 years and ≥60 years had relatively higher incidence of 974.89/105 and 132.33/105 respectively. Students constituted the predominant population, accounting for 34.81% (46 600 cases). Langzhong City ranked first in both total reported cases (23 659 cases) and average annual reported incidence (378.85/105). The overall spatial distribution of influenza cases was random. Low-high clusters were found in Gaoping District in 2017 and Xichong County in 2018; low-low clusters were observed in Yingshan County in 2020 and 2021; high-low clusters existed in Shunqing District in 2025. From 2016 to 2025, the overall positive detection rate of influenza virus among ILI was 15.03%, including influenza B Victoria lineage, influenza A H1N1 subtype, influenza A H3N2 subtype and influenza B Yamagata lineage. Conclusions The reported incidence of influenza in Nanchong City presented an upward trend from 2016 to 2025, with epidemics predominantly occurring in winter and spring. Males, children and adolescents, the elderly and students are high-risk population, while Langzhong City and Shunqing District are high-incidence areas. Different influenza subtypes circulate alternately or concurrently in this region.
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