Variation tendency and epidemiologic characteristics of influenza in Liao-ning province,2010-2014

Objective To examine epidemic situation and pathogenic characteristics of influenza in Liaoning province from 2010 to 2014 and to provide evidences for formulating preventive and control strategies.Methods Chi-square test and time series moving average method were used to analyze weekly data on influenza-like illness(ILI) from the 21 influenza sentinel hospitals and pathogen surveillance results of subtypes identified with hemagglutination inhibition test after viral isolation for specimens from ILI with Madin-Darby canine kidney(MDCK) cells from 2010 to 2014.Results During the 4-year period,the reported ILI cases accounted for 4.01% of all outpatient clinic visits(651241 out of 16 236264),with the yearly proportion of 3.79%,3.41%,4.59%,and 4.19%,respectively.The proportion of ILI in all outpatient clinic visits was significantly different among the months during a year(P<0.05).The ILI cases reported were mainly the people under the age of 15 years and 50% of the cases were small children aged 0-5 years.During the period,the yearly positive rate of influenza virus isolation were 1.20%,6.38%,7.35%,and 7.15%,with the dominant strain of H3N2,B,H3N2,and H1N1,respectively.The influenza outbreaks mainly occurred in winter and spring and at schools and childcare facilities.Conclusion The seasonal variation of influenza epidemic is obvious with a peak from December of a year to March of next year and the prevalent influenza strains are multiple with the alternations of dominant strains in Liaoning province from 2010 to 2014.