Surveillance for school absence due to influenza like illness in children in Hangzhou, Zhejiang, 2018–2020

  Objective  To evaluate the school absence due to influenza like illness (ILI) in children in kindergartens and schools in Hangzhou, analyze the correlation among the number of school absence due to ILI, the number of ILI cases in sentinel surveillance and the number of influenza cases reported in children during same period, and provide evidence for the early warning of influenza epidemic in schools.

  Methods  School absence surveillance data in kindergartens, primary and middle schools in Hangzhou from September 2018 to January 2020 (3 semesters) were used to analyze its correlation with sentinel surveillance data of ILI and reported incidence data of influenza in children with Spearman method.

  Results  The overall school absence due to ILI was 158 171 person-days in Hangzhou, the absence rate was 0.11%. The differences in absence rate among kindergartens, primary schools and middle schools were significant. The sentinel surveillance data of ILI were highly correlated with school absence surveillance data due to ILI in age group 5–14 years, (r=0.558, P<0.001). The number of influenza cases in young children and students was highly correlated with the number of school absence due to ILI, the correlation coefficient was highest at one week ahead (r=0.754, P<0.001).

  Conclusion  Children in kindergartens and primary schools are at high risk of ILI. School-based ILI surveillance plays an active role in influenza surveillance in kindergartens and schools.