Abstract
BackgroundSeasonal influenza epidemics occur annually with bimodality in southern China and unimodality in northern China. Regional differences exist in surveillance data collected by the National Influenza Surveillance Network of the Chinese mainland. Qualitative and quantitative analyses on the spatiotemporal rules of the influenza virus's activities are needed to lay the foundation for the surveillance, prevention and control of seasonal influenza.MethodsThe peak performance analysis and Fourier harmonic extraction methods were used to explore the spatiotemporal characteristics of the seasonal influenza virus activity and to obtain geographic divisions. In the first method, the concept of quality control was introduced and robust estimators were chosen to make the results more convincing. The dominant Fourier harmonics of the provincial time series were extracted in the second method, and the VARiable CLUSter (VARCLUS) procedure was used to variably cluster the extracted results. On the basis of the above geographic division results, three typical districts were selected and corresponding sinusoidal models were applied to fit the time series of the virological data.ResultsThe predominant virus during every peak is visible from the bar charts of the virological data. The results of the two methods that were used to obtain the geographic divisions have some consistencies with each other and with the virus activity mechanism. Quantitative models were established for three typical districts: the south1 district, including Guangdong, Guangxi, Jiangxi and Fujian; the south2 district, including Hunan, Hubei, Shanghai, Jiangsu and Zhejiang; and the north district, including the 14 northern provinces except Qinghai. The sinusoidal fitting models showed that the south1 district had strong annual periodicity with strong winter peaks and weak summer peaks. The south2 district had strong semi-annual periodicity with similarly strong summer and winter peaks, and the north district had strong annual periodicity with only winter peaks.
Highlights
The epidemic of seasonal influenza displays a seasonal pattern as well as the activity of seasonal influenza virus [1,2,3,4,5]
The number of sentinel hospitals and influenza laboratories was increased to 556 and 411 from 197 and 63, respectively. Before it was extended in June 2009, the National Influenza Surveillance Network had been comprised of 63 influenza laboratories and 197 sentinel hospitals across 31 provinces in the Chinese mainland
Geographic divisions based on influenza virus activity 1
Summary
The epidemic of seasonal influenza displays a seasonal pattern as well as the activity of seasonal influenza virus [1,2,3,4,5]. Influenza epidemics occur annually with marked winter peaks in most countries and regions in the northern hemisphere, such as the United States, Canada and Europe [6,7]. Surveillance in the Chinese mainland has shown a remarkable dual pattern of seasonal influenza: a regular winter pattern for northern China, which is similar to the regions listed above, and a different pattern for southern China. The main types of seasonal influenza surveillance data used in statistical analyses are usually mortality [9], Influenza-Like Illness (ILI) and virological data [6,10,11,12]. Meijer et al (2006, 2007 and 2008) conducted research on clinical and virological data on influenza from 33 countries collected by the European Influenza Surveillance Scheme (EISS) to assess influenza activity in Europe during the winters of 2004–2005, 2005–2006 and 2006–2007. Qualitative and quantitative analyses on the spatiotemporal rules of the influenza virus’s activities are needed to lay the foundation for the surveillance, prevention and control of seasonal influenza
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