Surveillance analysis of influenza-like illness in 1976 to 2017 in Xuhui District, Shanghai

ObjectiveTo analyze the epidemiologic and laboratory surveillance data from Xuhui District Central Hospital in 1976 to 2017, and to describe the long-term trend and epidemiological characteristics of influenza-like illness (ILI) epidemics in Xuhui district.

MethodsThe surveillance data on ILI in the influenza surveillance sentinel hospitals in Xuhui District of Shanghai from 1976 to 2017 were collected and analyzed, and the results of isolation and identification of influenza viruses in the CDC of Xuhui District from 2005 to 2017 were reviewed and analyzed.

ResultsIn most years from 1976 to 2017, there were two peaks of ILI, one was the winter epidemic peak from December to January, and the other was the summer epidemic peak in July and August.From 2004 to 2017, the top age group each year was 25-year-old group; from 2004 to 2011, 15-year-old group and 60-year-old group were alternately in the second place; from 2012 to 2017, 60-year-old group was always in the second place.The constituent ratio of the 0 to 5-year-old group decreased significantly after 2008.The results of influenza etiology test from 2005 to 2017 showed that most strains of influenza A and B appeared alternately, and most of them changed around June.In 2007, B strains appeared in summer, and after 2010, B strains mostly appeared in winter and spring.The peak rate of influenza like illness reached the peak of positive rate of virus detection from 2009 to 2017.

ConclusionFrom 1976 to 2017, there were two epidemic peaks of influenza like illness in winter and summer, and the epidemic intensity in summer was higher than that in winter.A and B strains alternated regularly. The 25-year-old group was in the first place of ILI proportion.