A Waterborne Shigellosis Outbreak in a Primary School, Tai-Chung City, November 2007

Yen-Nan Chao

2008 Vol.24 NO.10

Correspondence Author： Yen-Nan Chao

Abstract：

Shigellosis is mainly transmitted from person-to-person. Contaminated water or foods can also cause large outbreaks. This study was to evaluate the transmission route and to find the possible common source associated with a waterborne outbreak caused by Shigella sonnei in a primary school in Tai-Chung City, Taiwan, in November 2007.
We conducted a case-control study of students in the school on November 22nd, 2007. Cases were defined as illness on students who had diarrhea or at least two of the following symptoms: fever, vomiting, tenesmus, or abdominal pain. We used questionnaire included information about demographic data, hand hygiene, type of lunch, drinking water, and school cleaning assignments. Rectal swabs were collected from suspect cases and their contacts. We also inspected the school environment. Stool and water samples were sent for cultures and pulsed-field gel electrophoresis (PFGE).
There were 271 suspect cases occurred during the 4 weeks before investigation. A total of 57 confirmed cases were found in the end of outbreak. Poor hand hygiene after toilet was associated with illness (OR: 1.64; 95% CL: 1.07-2.52). Environmental investigation revealed that groundwater for lavatory-use in four of the six school buildings was contaminated by a damaged sewer connection. Students whose classrooms located in the four buildings had higher attack rate in the study. (16.7% vs. 8.2%, p < 0.001). The water sample yielded Shigella sonnei which was identical to human isolates in PFGE pattern.
Conclusion. It was a shigellosis waterborne outbreak and lasted for another two weeks after carrying out the control measures. It did not spread to the community. Tai-Chung City government then prohibited any groundwater use in schools and increased the budget for them to access piped water system. Water quality examination should also be done in each semester.
Keywords: Shigella sonnei, waterborne outbreaks, groundwater