Incidence, circulation, and spatiotemporal analysis of seasonal influenza in Shandong, China, 2008–2019: A retrospective study

Abstract

Background: Understanding the influenza-like illness (ILI) incidence, circulation pattern of virus strains and spatiotemporal pattern of influenza transmission are important for designing control interventions. Based on the 10 years' surveillance data, we aimed to provide a baseline characterization and the epidemiology and dynamics of influenza virus in Shandong. Methods:We extracted surveillance and laboratory testing data. We estimated the ILI incidence and analyzed the predominant virus. A wavelet power analysis was used to illustrate the periodicity. In addition, we applied a linear regression model to characterize the correlation of influenza seasonality with longitude. Results: The average ILI incidence was estimated to be 3744.79 per 1 million (95% confidence interval [CI]: 2558.09-4931.45) during 2009-2018. Influenza A/H1N1and A/H3N2 strains predominated in the most influenza seasons in Shandong. The annual amplitude of influenza epidemics decreased with longitude (P < 0.05). In contrast, the epidemic peak of influenza emerged earlier in the western region and increased with longitude in influenza A (P < 0.05). The annual peak of the influenza B epidemic lagged a median of 4.2 weeks compared with that of influenza A. Conclusions:The development or modification of seasonal influenza vaccination strategies requires the recognition that the incidence is higher in preschool-and school-aged children. Although seasonal influenza circulates annually in Shandong, the predominant virus strain circulation pattern is extremely unpredictable and strengthening surveillance for the predominant virus strain is necessary. Lower longitude inland regions need to take nonpharmaceutical or pharmaceutical interventions in advance during influenza high-occurrence seasons.

Heterogeneity of influenza infection at precise scale in Yinchuan, Northwest China, 2012–2022: evidence from Joinpoint regression and spatiotemporal analysis

“…Regarding seasonal trends, influenza in China varies with latitude and shows diverse spatial patterns and seasonal characteristics 23 . Similar to other reports 25 , 33 , influenza in Yinchuan displayed an unimodal mode, with the peak appearing from December to March. Notably, the low influenza incidence appeared in July and August, in keeping with the school holiday and population mobility peak.…”

“…Some researchers 22 , 24 , 25 have applied spatial techniques and geographic information systems to probe the geographic distribution characteristics and identify influenza clusters for high and low-risk regions and periods in China. Most of them emphasized the geographic heterogeneity of influenza at the urban level in economically developed cities.…”

Dynamics of influenza‐like illness under urbanization procedure and COVID‐19 pandemic in the subcenter of Beijing during 2013–2021

“…ILI seasonal outbreaks showed similar epidemic size and intensity before urbanization during 2013–2016, despite the ongoing changes of local climate or influenza virus mutation. We suppose this might due to the stable resident population and limited human mobility that restricted the internal and external transmission routes of the virus 23 . During the transition period of urbanization from 2017 to 2018, ILI intensity showed a generally transient decrease.…”

“…We suppose this might due to the stable resident population and limited human mobility that restricted the internal and external transmission routes of the virus. 23 During the transition period of urbanization from 2017 to 2018, ILI intensity showed a generally transient decrease. It was mainly attributed to the declined rate of ILI among children and adolescents in terms of their less advanceable clinic access among this population.…”

Genetic characterization and whole-genome sequencing-based genetic analysis of influenza virus in Jining City during 2021–2022

“…Currently, the seasonal influenza virus pathogens that infect humans are mainly influenza A H1N1 influenza virus, seasonal influenza A H3N2 subtype virus, B Victoria series influenza virus, and B Yamagata series influenza virus ( Wu and Wilson, 2020 ). These four influenza viruses alternate in prevalence during different years ( Liu et al, 2022 ).…”