Analysis of spatial and temporal aggregation of influenza cases in Quzhou before and after COVID-19 pandemic.

Background: The global seasonal influenza activity has decreased during the coronavirus disease 2019 (COVID-19) pandemic. Non-pharmaceutical interventions (NPIs), such as reducing gatherings and wearing masks, can have varying impacts on the spread of influenza. We aim to analyse the basic characteristics, epidemiology and space-time clustering of influenza in Quzhou city before and after the COVID-19 pandemic based on five years of surveillance data.

Methods: Influenza case incidence data from 2018-2023 were collected and organized in Quzhou City to analyse the space-time aggregation of influenza incidence before and after COVID-19 pandemic through global spatial autocorrelation analysis and space-time scan analysis methods.

Results: The annual average fluctuation of influenza in Quzhou City from 2018-2023 was large, with gradual decreases in 2019-2020, 2020-2021 and 2021-2022, all of which showed obvious winter and spring peaks; The highest incidence rate in 2022-2023, with a bimodal distribution. The majority of the population is under 15 years of age, accounting for more than 70% of the population. The population classification is dominated by students, nursery children and children in the diaspora. In 2020-2021, the cases in the student group of the 5-14 years old population declined. Global spatial autocorrelation analysis of influenza incidence rate in Quzhou City in each year of 2019-2023Moran's  > 0 and  < 0.05. Space-time scan analysis of the aggregation area is located in Longyou County and the township streets on the border of urban counties, and the number of aggregation areas decreased significantly in 2020-2021 and 2021-2022.

Conclusion: The COVID-19 pandemic has an important impact on changes in influenza incidence levels and spatial and temporal epidemiologic aggregation patterns. Influenza incidence in Quzhou City fluctuates widely, with large changes in the age and occupational composition ratios of the incidence population, and influenza incidence presents a more pronounced spatial correlation and aggregation.