[Outbreak of listeriosis in Valais, 2020: review of causes of food contamination.]

Listeria monocytogenes, a gram-positive bacterium, is the cause of Listeriosis. Its mortality is currently the highest for food borne diseases. Affected are mainly elderly or immunocompromised patients, as well as pregnant women. Despite food hygiene measures and surveillance, outbreaks are possible in developed countries. In the canton of Valais, six hospitalized cases including one death occurred between end of March and the beginning of May 2020. The typing of these strains of L. monocytogenes showed a link to a larger Swiss outbreak associated with contaminated soft cheese (Brie). The outbreak ended once the producer recalled the incriminated cheese. This article describes the outbreak with a review of other outbreaks' sources and a reminder of preventive measures.