Occurrence of Listeria monocytogenes in the Swiss food supply (2015–2024)

Abstract Listeriosis, caused by Listeria monocytogenes ( Lm ), is a severe foodborne illness predominantly affecting high-risk groups, and has a high case fatality rate. Switzerland has experienced several outbreaks, but a national overview of implicated foods is lacking. We reviewed foodborne listeriosis in Switzerland, investigating Lm presence in food and foods linked to outbreaks. Epidemiological data, data on official sampling, reporting and outbreaks were collected from government agencies and the literature. Between 2015 and 2024, on average 53 listeriosis cases were reported annually (incidence 0.61/100,000), with highest incidences in adults over 65 years old and children under one year old. Official sampling found Lm most commonly in meat and meat products (38% of positive samples), ready-to-eat foods (22%) and fish and fish products (7.9%). Among cantons with available data (13 out of 26 cantons), common serogroups and serotypes were serogroup IIa (serotypes 1/2a or 3a; 31%), serotype 1/2a (20%), serogroup IVb (serotypes 4b, 4d, 4e; 19%) and serotype 4b (14%). There were 25 recalls and 36 public warnings due to Lm . Eleven listeriosis outbreaks with a confirmed link to food were identified in Switzerland since 1983, with case fatality reaching 29%, involving both ready-to-eat and non-ready-to-eat foods of animal and plant origin. Non-ready-to-eat foods were likely associated with outbreaks through cross contamination. National legislation should be expanded to address cross-contamination risks posed by non-ready-to-eat products. A new genomic national information system is planned, which will enhance outbreak investigation, improving timely prevention and control of listeriosis.