Abstract: Objective  To understand the epidemic characteristics of influenza in Tongling City for evidence in prevention and control of influenza in this area. Methods  Data of influenza-like cases (ILI), together with surveillance data on the etiology and influenza outbreak in Tongling were collected from 2015 to 2020 through Chinese Influenza Surveillance Information System, and analyzed for the distribution of ILI and epidemiological characteristics, including the population with positive virus samples, time distribution and virus classification. Results  A total of 26 862 ILI cases were reported in 2 sentinel hospitals of Tongling from 2015 to 2020. ILI cases were dominated by children under the age of 5 (46.04%, 12 367/26 862).The average ILI% was 3.11% (26 862/862 671), with difference among years (χ2=941.478, P<0.05) . Eight peaks were observed in the monitoring year, primarily seen in winter and spring. In total, 8 490 case samples were collected, of which 1082 were positive (12.60%). The positive rate was 14.44% (586/4 059) and 11.19% (496/4 431) for males and females, respectively, and the highest in population aged between 5 and 14 years (22.41%, 322/1 437). The positive rate was relatively higher between 2017 and 2018 (20.63%, 255/1 236), and was different among genders, ages and years (χ2=20.038, 249.020, 941.478, respectively; all P<0.05). The dominant strains of influenza were differently epidemic in each surveillance year. Influenza A(H1N1) pdm09 virus and influenza A(H3N2) were prevalent, yet influenza B/Victoria and B/Yamagata were alternately prevalent in each surveillance year. A total of 20 influenza outbreaks were reported, all of which were in primary and secondary school students. Conclusion  The influenza usually waves in winter and spring seasons in Tongling City, and primarily affect population between 5 and 14 years of age. The results suggest that it is necessary to strengthen the vaccination of students before the epidemic peak and surveillance in key places.

Key words: Flu, Influenza-like cases, Outbreak, Epidemiological characteristics, Tongling City