Nontyphoidal Salmonella is a main cause of bacterial food-borne infection in Europe [1,2]. The majority of human infections is caused by a limited number of Salmonella serotypes among the 2,600 described to date [3,4]. Salmonella enterica serotype Dublin (S. Dublin) is particularly invasive in humans and more often leads to severe disease and higher mortality rates compared with other serotypes [4–7]. S. Dublin is host-adapted to bovines and is frequently isolated from cattle, with raw milk or raw-milk cheeses as a typical vehicle for food-borne outbreaks [8,9].
In 2012, a major S. Dublin outbreak occurred in France, with 103 cases linked to Saint-Nectaire (bovine raw-milk cheese) consumption [10,11]. In 2015, 34 S. Dublin cases were reported linked to the consumption of Reblochon (bovine raw-milk cheese) (data not shown; Santé publique France).
In France, the National Reference Center for Salmonella (NRC) and the French Agency for Food, Environmental and Occupational Health and Safety (ANSES) routinely collect and serotype human and non-human Salmonella isolates, respectively [12–14], using the Kauffmann–White–Le Minor scheme . The S. Dublin isolates collected are frequently susceptible to all antibiotics and show an indistinguishable pulsed-field gel electrophoresis (PFGE) pattern. To better distinguish S. Dublin isolates, multilocus variable-number tandem repeat analysis (MLVA) has recently been used for surveillance and outbreak investigations [11,15]. Moreover, whole genome sequencing (WGS) of Salmonella has been shown to discriminate between closely related isolates of S. Dublin [16,17].
On 18 January 2016, the French NRC reported to Santé publique France (SpFrance, the French national public health agency) an excess of S. Dublin infections across the country, with 37 S. Dublin isolates identified between mid-November 2015 and mid-January 2016, compared with 10 S. Dublin isolates during the same period in the two previous years. An outbreak investigation team with experts from SpFrance, NRC, ANSES and the French Directorate General for Food (DGAL) launched extensive epidemiological, microbiological and food investigations to confirm the outbreak, identify the vehicle of transmission and propose appropriate control measures.
Disentangling a complex nationwide salmonella Dublin outbreak associated with raw-milk cheese consumption, France, 2015 to 2016,
Aymeric Ung1,2,3, Amrish Y. Baidjoe3,4,5, Dieter Van Cauteren1, Nizar Fawal5, Laetitia Fabre5,Caroline Guerrisi6, Kostas Danis1,2, Anne Morand7, Marie-Pierre Donguy7, Etienne Lucas1,Louise Rossignol6, Sophie Lefèvre5, Marie-Léone Vignaud8, Sabrina Cadel-Six8, Renaud Lailler8,Nathalie Jourdan-Da Silva1,9, Simon Le Hello5,9