Varicella outbreak among primary school students--Beijing, China, 2004

Area of Science:

• Epidemiology
• Infectious Disease Control
• Public Health

Background:

• A significant varicella (chickenpox) outbreak occurred in a Beijing primary school in June 2004.
• The outbreak affected a high percentage of children, necessitating an investigation into transmission dynamics.

Purpose of the Study:

• To identify factors contributing to the high transmission rate of varicella in a primary school setting.
• To evaluate the effectiveness of implemented control measures during the outbreak.

Main Methods:

• Case definition: generalized vesicular pruritic rash >4 days in students between January 1-June 26, 2004.
• Data collection: parent interviews on prior varicella history, exposure, and vaccination status.
• Comparative analysis: 111 ill students versus 120 control students.

Main Results:

• High attack rates (>40%) observed in classrooms where infected students remained in school for 2 days.
• Secondary attack rate was 21% when ill students stayed in school versus 1.7% when sent home immediately (RR=10).
• Ill students were more likely to use school buses (OR=4.9) and less likely to have prior varicella vaccination (OR=0.22).

Conclusions:

• Failure to exclude students promptly on the first day of rash significantly contributed to varicella spread.
• High susceptibility at school entry highlights the importance of vaccination for controlling recurrent outbreaks.