Abstract: Objective To find out the extent, pathogen and infection source of a diarrhea outbreak in a middle school in Fuyang, Zhejiang province and provide evidence for the control of the epidemic. Methods Suspected cases, who had nausea, vomiting, fever(≥37.5 ℃), abdominal pain, abdominal distension and other clinical symptoms from 17 to 20 October, were searched according to the medical records in school medical room, Fuyang Proplr's Hospital and Fuyang Traditional Chinese Medicine hospital and through the communicable disease automatic warning system of China CDC. The suspected cases who had ate food from school store during the outbreak and the students without any clinical symptom were selected as case group and control group, respectively, to carry out a 1:4 case-control study. Results The egg sandwich from school store was identified as risk factor. The differences in attack rate between males and females and between students and teachers had statistical significance(χ2=5.24,P=0.02),(χ2=6.54,P=0.01). Ten Salmonella strains were detected with antigens of O1, 9, 12 and Hg, p, all belonged Salmonella dublin. The PFGE pattern analysis indicated that the 10 strains shared the 100% homology. Conclusion The epidemic was caused by the contamination of egg sandwich with S.dublin due to the insufficient cooking of eggs.