Surveillance of varicella-induced absenteeism in primary and secondary school students in Minhang District， Shanghai， 2021

Objective To analyze the varicella cases from the illness-induced absenteeism system and the National Notifiable Disease and Reporting System （NNDRS） in primary and secondary school students in Minhang District， determine the characteristics of varicella-induced absenteeism in schools， and provide scientific evidence for the prevention and control of varicella in schools.

Methods Surveillance data of varicella-induced absenteeism and varicella cases in the NNDRS in 2021 were collected. Characteristics of varicella-induced absenteeism and consistency of data between the illness-induced absenteeism system and the NNDRS were determined， using descriptive analysis and matching varicella cases in the two systems.

Results The incidence of varicella in Minhang District was 48.28/10⁵ in 2021. The overall rate of illness-induced absenteeism was 612.08/10⁵ in primary and secondary schools， and the rate of varicella-induced absenteeism was 6.03/10⁵. The distribution of varicella-induced absenteeism was consistent with the incidence of varicella cases. Furthermore， the rate of varicella-induced absenteeism was significantly higher in boys than in girls. The rate increased synchronously during the peak of varicella incidence. The rate differed significantly across the students in diverse schools （χ²=135.217，P<0.001）， which was the highest in middle school students. However， there was no significant difference in the number of absent days between peak incidence and non-peak incidence periods of varicella （t=0.173， P=0.863）. Moreover， actual matching proportion of varicella cases between illness-induced absenteeism system and the NNDRS was 88.90%. The varicella cases that had been notified and those had not been notified in the NNDRS did not differ significantly in the number of absent days （t=0.346， P=0.730）.

Conclusion The incidence of varicella and varicella-induced absenteeism in schools is relatively low in Minhang District. Data between the illness-induced absenteeism system and the NNDRS is consistent. Routine prevention and control of varicella in schools is maintained a good level throughout the year.