Abstract: Objective To investigate the epidemiological characteristics and analyze the risk factors of an infectious diarrhea outbreak in a factory in Shenzhen City, so as to provide scientific evidence for decision-making in the prevention and control of diarrhea outbreaks. Methods All cases were screened according to the case definition. The epidemiologic characteristics were described to facilitate proposing etiological hypothesis, followed by retrospective cohort study and case-control analyses to determine the risk factors. Anal swabs of patients and cooks, and samples of the outer environment were collected for pathogenic detection. The real time fluorescent quantitative RT-PCR was used for detection of virus nucleic acid and the PCR amplified products were sequenced to identify the virus genotyping. Results A total of 76 cases were found from 17 to 21 January 2013, with an attack rate of 18.12%（76/414）. The attack rates in general staff, middle-level staff, and senior staff were 26.28% (72/274), 2.96% (4/135）, and 0.00%（0/5）, respectively（P<0.01）. The retrospective cohort study analysis showed that the attack rate in middle-level staff who ate meals serving for the general staff was 11.43%（4/35）, while there was no case in middle-level staff who didn’t (0/75）（P<0.01）. Case-control study showed that on January 15th, the proportions of cases who ate the first round vegetables for lunch and dinner were 64.00%（32/50）and 70.83%（34/48）respectively in the case group, and those were 41.67%（35/84）and 50.00% (40/80) in the control group, and the ORs were 2.489（95%CI: 1.209-5.125）and 2.429（95%CI: 1.134-5.199）, respectively, indicating the exposure to the first round vegetables of the lunch and dinner was a risk factor for the outbreak. Sixty-four samples of rectal swabs of patients and cooks,vomit, feces,hand swabs, food, spices, kitchen utensils, and water were collected. Pathogenic bacteria were negative in 56 samples detected. Among the 51 samples for detection of norovirus nucleic acid, 13 rectal swabs of patients, 2 rectal swabs of cooks, 2 feces of patients and 1 patient vomit were positive for the norovirus nucleic acid and all were identified as the GII-4 norovirus Sydney 2012 strain. Conclusion This infectious diarrhea outbreak may be caused by vegetables contaminated with the new GII-4 norovirus Sydney 2012 strain. Health education should be strengthened among food-processing workers.