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

From January 2008 to December 2015, Center for Disease Control and Prevention of Xicheng District in Beijing recorded 1 294 279 ILI visits and a total of 41 269 165 clinic attendances. Percentage of number of ILI visits to number of total clinic attendances (ILI%) had been widely used as an indicator for influenza activities. 15 Figure 1A illustrates age-specific trends in weekly ILI% throughout 8 years. Peaks of influenza activities appear from end of December to middle of January across different age groups in the past years. Summer peaks were observed for groups of age 0-4 and 5-14 without a consistent annual pattern. During the winter school breaks, ILI incidence decreased substantially in age groups of 5-14 and 15-24, but modestly in age groups over 25 (figure 1B). During the summer school breaks, only ILI incidence in age group of 5-14 reduced dramatically, while levelled off for other age groups (figure 1B). A decline of schoolchildren-to-adults IRR during school breaks implied an age shift in patients with ILI towards adults, and further suggested a reduction of influenza transmission among schoolchildren.