Effects of school breaks on influenza-like illness incidence in a temperate Chinese region: an ecological study from 2008 to 2015

Chu, Yanhui; Wu, Zhenyu; Ji, Jiayi; Sun, Jingyi; Sun, Xiaoyu; Qin, Guoyou; Qin, Jingning; Xiao, Zheng; Ren, Jian; Qin, Di; Zheng, Xueying; Wang, Xi-Ling

Beijing is located in northeastern China and has a temperate and continental climate with four distinct seasons. Xicheng District is located in the centre of Beijing. Weekly district-wide ILI time series during 2008-2015 was obtained from Beijing Medical Institutions in Communicable Disease Surveillance and Early Warning System. ILI was defined as fever (temperature of 38°C or greater) and a cough and/or a sore throat in the absence of a known cause other than influenza. The ILI reporting system recorded weekly ILI cases into five age groups (0-4, 5-14, 15-24, 25-59 and 60 years or older). Beijing Children's Hospital, affiliated with Capital Medical University is one of the sentinel hospitals for ILI surveillance, and accounts for more than half of the total paediatric outpatient visits in Beijing. To render our data more representative of ILI rates across the entire Beijing population, we age-standardised our ILI visit data in Xicheng District to the age distribution of Beijing's population.