Investigation and analysis of a varicella outbreak in a middle school in Jiangbei District of Chongqing City in 2023
Objective To analyze the characteristics of a varicella outbreak that occurred in a middle school in Jiangbei District of Chongqing City in 2023,and to provide experience for disease prevention and control.Methods The Epidemiological Investigation Form for Varicella Cases was used to conduct an epidemiological investigation among varicella cases in the varicella outbreak that occurred in the middle school in Jiangbei District of Chongqing City in 2023.Descriptive epidemiological methods were used to analyze the epidemiological characteristics,including the attack rate,clinical manifestations,the vaccination status of chickenpox vaccine.Statistical analysis was performed by SPSS 22.0 statistical software.The difference in the attack rate was examined by x2 test,and pairwise comparison of rates was examined by Bonferroni test.The test level was α=0.05,and α'=α/3=0.017 when pairwise comparison.Results A total of 49 varicella cases were reported in this outbreak,with a total school attack rate of 1.26％(49/3 878).The largest number of cumulative cases was found in grade 7,with 36 cases and an attack rate of 3.76％(36/957).The attack rate in grade 8 was 0.94％(10/1 066),and 1.06％(3/284)in grade 1 of high school,respectively.There was a statistically significant difference in the attack rate of varicella cases among different grades(x2=26.117,P=0.006).Pairwise comparison analysis found that there was a statistically significant difference in the attack rate between grade 7(3.76％)and grade 8(0.94％)(x2=18.094,P＜0.001),grade 7(3.76％)and grade 1 of high school(1.06％)(x2=15.266,P＜0.001),while there was no statistically significant difference in the pairwise comparison between grade 8(0.94％)and grade 1 of high school(1.06％)(x2=0.330,P=0.856).The clinical manifestations of the 49 cases were mainly rash(49/49,100％)and fever(22/49,44.90％),with herpes(37/49,75.51％)as the main rash.The rash mainly occurred on the head and neck(38/49,77.55％).There were 25 males and 24 females,with a gender ratio of 1.24:1.The age of cases ranged between 12 and 15 years old.A total of 9 cases did not receive varicella vaccine(18.37％),27 cases had a history of receiving varicella vaccine(55.10％),and 13 cases had an unknown vaccination history(26.53％).Conclusions The varicella epidemic was caused by the indicating cases returning to school before the end of the quarantine period,coupled with poor ventilation in the classroom.If the isolation measures of infected students cannot be implemented,it will cause cross-class outbreaks,making it difficult to control the epidemic in a short period of time.
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