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OBJECTIVE On 4 March 2010, the Department of Epidemiological Surveillance and Intervention of the Hellenic Centre for Disease Control and Prevention was notified about an outbreak of gastroenteritis among high school pupils who had stayed at a hotel of the Prefecture of Central Macedonia from 11 to 15 February 2010, in the context of a school excursion. The aim of this study was to detect the possible source of the outbreak and to define the mode and the vehicle of disease transmission. METHOD A retrospective cohort study was conducted. Individuals who had participated in the school excursion were interviewed via a structured questionnaire, which covered demographic data and information about the disease and possible exposures. Epidata v3.1 was used for data entry and STATA v11.0 for data analysis. Relative risks (RR) and 95% corresponding confidence intervals (CI) were computed for all the risk factors tested. An association was considered statistically significant when the p value was <0.05. The presence of statistically significant independent associations was examined via multiple logistic regression using backward elimination techniques. Risk factors for which the univariate analysis showed a p value <0.05 and RR >3 were included in the multivariate analysis model. A culture was ordered for one stool sample taken from a student. The Health Directorate conducted an environmental inspection of the hotel's kitchen premises and the procedures followed during food preparation. RESULTS Of the 61 persons who participated in the excursion, 54 were included in the study (88.5%). The attack rate was 27.8%. Univariate analysis showed statistically significant association of the disease with several food items that had been consumed during the pupils' stay at the hotel, but the only statistically significant risk factor derived from the multivariate analysis was the consumption of pasta with carbonara sauce at the dinner of the fourth day (RR=17.5, 95% CI: 2.47-123.8). Results of the stool culture were negative. The environmental investigation detected several deficiencies regarding hygiene measures and some food items that were found inappropriate for consumption were confiscated. CONCLUSIONS Even in cases where the laboratory verification of an outbreak is not possible, the epidemiological investigation of an outbreak of gastroenteritis can be of great use, as it provides information regarding the possible source and the mode of the disease transmission. [ABSTRACT FROM AUTHOR]