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Introduction: During July 9-14, 2004, an outbreak of gastroenteritis occurred among workers at an electronics factory in Huizhou, Guangdong Province, China; 199 cases were reported. A case-control investigation was initiated to identify the agent and the mode of transmission. Methods: Stool samples were collected from 142 workers and food handlers and cultured for enteric pathogens. A questionnaire concerning meals and foods eaten in the factory cafeteria during July 11-13 was administered to 92 ill workers and 100 controls. Results: Of approximately 2,000 workers who worked during the outbreak, 197 (10%) had illness consistent with the case definition. Salmonella enteritidis was identified from 44 (31%) of 142 stool samples collected from ill workers. Ill workers were more likely than controls to have eaten breakfast in the factory cafeteria during July 11-13. Of eight foods served at breakfast in the factory cafeteria, three were associated with illness: cake, bread (on July 12 only), and congee (i.e., rice porridge). Stratification of bread and congee exposure by cake consumption indicated that only bread eaten on July 12 was associated with gastroenteritis. The cake was baked on July 11, and a mixture that included raw eggs was poured on top; the cake was then stored at room temperature and served for breakfast on 3 consecutive days (July 11-13). The bread was stored together with the cake on July 11 and 12. No leftover food was tested. Discussion: The investigation indicated that an outbreak of S. enterica serotype Enteritidis resulted from consumption of an unusual food vehicle (i.e., cake) that had been contaminated from a more typical source (i.e., raw eggs). The bread was stored at room temperature together with cake on which a mixture made from raw eggs had been poured. The bread was probably contaminated by contact with the cake. Conclusion: Food handlers should be instructed that intact fresh eggs can harbor S. enteritidis, foods made from eggs must be cooked, and prepared food must be stored under refrigeration. [ABSTRACT FROM AUTHOR]