Epidemiological characteristics of influenza-like illness outbreaks in Wuhan, 2012-2017

Objective To understand the epidemiological characteristics of influenza-like illness (ILI) outbreaks in Wuhan city from 2012 to 2017, and to provide a scientific basis for influenza prevention. Methods Information of the ILI outbreaks reported in the city from 2012 to 2017 was collected for the analyses of time, places and virus types of the outbreaks. Results A total of 19 ILI outbreaks were reported in the city from 2012 to 2017. Fifteen outbreaks were laboratory confirmed, including 11 outbreaks caused by influenza B virus (73.33%). Of the 19 ILI outbreaks, 16 (84.21%, 16/19) occurred in schools, including 11 outbreaks (57.89%, 11/19) in primary schools. The medians value of time intervals between the index case onset to the reporting was 7 (1-20) days, and the medians value of duration of the outbreaks was 25 (10-46) days. The time interval was positively correlated to duration of outbreaks (r=0.71, P<0.01). Conclusions ILI outbreaks occurred mainly in primary schools in Wuhan from 2012 to 2017. Timely reporting of the outbreaks and early implementation of control measures were the key points to control influenza outbreak. Key words: Influenza; Influenza-like illness; Epidemiological characteristics