Introduction - Two outbreaks of foodborne illness were reported among employees of the same company following seminars held at two seaside resorts in Loire-Atlantique between January 26 and 29, 2010. Methods - A retrospective study was conducted on the two cohorts comprising the seminar participants (n = 69). Viral testing was performed on stool samples from the patients, on shellfish suspected of causing the contamination, and in the environment of shellfish farms. Results - Thirty-seven (37) cases of gastroenteritis were identified. Investigations identified two distinct outbreaks attributed to shellfish consumption. The symptoms and median incubation period were consistent with the detection of norovirus in both patient stool samples and representative samples of oysters and mussels consumed. Conclusion - The diversity of clinical viral strains supported the conclusion that the norovirus outbreaks were attributable to the consumption of shellfish. The first episode attributed to oyster consumption was part of a cluster of 4 foodborne illness cases that led to recall measures and a fishing ban in an oyster-farming area of Morbihan. These outbreaks underscore the importance of combining viral testing with stool cultures when investigating foodborne illness linked to shellfish consumption. (R.A.)