Abstract
A European multi-country outbreak of Salmonella Enteritidis phage type (PT) 14b occurred from March to November 2014 associated with the consumption of eggs. The outbreak involved more than 400 human cases from France, Luxembourg, Austria and the United Kingdom. In 2016–2017, it has been re-evaluated combining recent epidemiological results with latest molecular data. The outbreak was traced back to one large Bavarian egg producer with four distinct premises, three located in Bavaria, one in the Czech Republic. The outbreak isolates of S. Enteritidis PT 14b were grouped into three closely related clades by whole genome sequencing. Two of these clades could be referred to two Bavarian premises of the egg producer on the basis of epidemiological and molecular data, while epidemiological data presumably linked the third clade to another premises of the egg producer. Interestingly and in contrast to the situation in other European countries where several outbreaks were documented, all notified 91 laboratory-confirmed cases of S. Enteritidis PT 14b from Bavaria were sporadic, singular cases not belonging to any epidemiological outbreaks. In conclusion, as demonstrated here, the resolution of food-related outbreaks with such a high discriminatory power is rare in outbreak investigation.
Highlights
In 2014, 88,175 confirmed cases of human salmonellosis causing 9,830 hospitalisations and 65 fatalities were reported across the European Union (EU)
Comprehensive outbreak investigations require the combination of epidemiological data and molecular typing techniques, especially if bacteria with a very low natural mutation rate such as Salmonella spp. are concerned
Low discriminatory typing techniques like phage typing or multilocus variablenumber tandem repeat analysis (MLVA) typing may be well suited for investigating small, circumscribed, local outbreaks
Summary
Enteritidis) is one of over 2,600 serovars of the genus Salmonella with zoonotic potential and often associated with food-borne human disease. S. Enteritidis forms a strongly clonal group with low genetic heterogeneity, whose members can be sufficiently discriminated from each other only by modern molecular techniques [1,2,3,4,5,6]. The incidence of human salmonellosis has decreased steadily in recent years. In 2014, 88,175 confirmed cases of human salmonellosis causing 9,830 hospitalisations and 65 fatalities were reported across the European Union (EU). 16,000 cases of human salmonellosis were reported from Germany. Enteritidis was the predominant serovar (44.4% of all isolates) followed by S. Typhimurium, monophasic variant (7.8%) [7]
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