Surveillance of influenza in Liaoning province, 2011-2012

Objective To understand epidemiological characteristics of influenza and the distribution of predominant virus strain in Liaoning province from 2011 to 2012, and provide evidence for the prevention and control of influenza. Methods Descriptive analysis was conducted on the incidence data of influenza like illness (ILI) and pathogen surveillance results from the influenza sentinel hospitals in Liaoning from 2011 to 2012. Results During this period, the proportion of ILI treated by hospitals was 3.34%, a slight decline compared with previous influenza season. The incidence peaks occurred in spring and winter. Totally 540 strains of influenza viruses were isolated, the isolation rate was 6.38%. Influenza B virus was predominant during the whole surveillance period. Etiological surveillance results revealed that multi type viruses circulated alternatively or co-circulated with obvious seasonality. Predominant strain changed at late phase of the influenza season from Influenza B virus/Yamagata lineage to seasonal influenza A (H3N2) virus or B virus/Victoria lineage. The ILI proportion was positively correlated with virus isolation rate (correlation coefficient: 0.648, PConclusion The incidence peaks of influenza were in spring and winter in Liaoning. The predominant strain varied with season and might be influenza A (H3N2) virus and B virus/Victoria lineage in the second half of 2012.