In late December 2007, a local hospital in the Var region reported an outbreak of acute gastroenteritis (AGE) cases, likely of viral origin, to the Departmental Directorate of Health and Social Affairs. An epidemiological investigation was conducted to identify the cases and provide recommendations for controlling the outbreak. Case identification was based on reports from the hospital. The number of cases among patients and staff, as well as the period of occurrence, were recorded for each department. Stool cultures were performed to detect bacteria and viruses. Over the course of one month, 159 cases were identified: 25 were staff members (attack rate: 22%) and 134 were patients (attack rate: 46%). The clinical presentation was mild, and patients recovered within 24–48 hours without hospitalization. The hospital is located on two sites connected only by staff and food services. The first site comprises two buildings, one of which is three stories tall. The outbreak began on the 2nd floor of a building at the first site with 29 cases, then spread to the 1st floor (15 cases) and the 3rd floor (3 cases). The outbreak then spread to the second building at the same site (72 cases) and finally to the second site (40 cases). Among the stool cultures performed, the same strain of norovirus was isolated in three samples. Despite the lack of individual data, the clinical presentation supports a viral etiology for the outbreak. The norovirus strains found in the stool samples of 3 cases support this hypothesis. The outbreak spread rapidly due to the very high contagiousness of noroviruses but also due to the lack of case isolation. Indeed, it is likely that residents moving between floors within the same building contributed to this spread across the different units. However, since several sites were affected in succession, it is likely that staff played a role in the spread of the outbreak. It is important to note that upon the emergence of cases of acute gastroenteritis, rigorous hygiene measures must be implemented very quickly to limit the spread of an outbreak. The delayed reporting did not allow for the containment of the pathogen’s spread within the facility, underscoring the importance of early notification of the relevant departments. (R.A.)