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. 2015 Feb 10:7:ecurrents.outbreaks.2c05a47d292f376afc5a6fcdd8a7a3b6.
doi: 10.1371/currents.outbreaks.2c05a47d292f376afc5a6fcdd8a7a3b6.

Whole Genome Sequencing for the Retrospective Investigation of an Outbreak of Salmonella Typhimurium DT 8

Philip M Ashton  1 , Tansy Peters  2 , Linda Ameh  2 , Ralph McAleer  3 , Stewart Petrie  3 , Satheesh Nair  2 , Ivan Muscat  4 , Elizabeth de Pinna  2 , Tim Dallman  2
Affiliations

Whole Genome Sequencing for the Retrospective Investigation of an Outbreak of Salmonella Typhimurium DT 8

Philip M Ashton et al. PLoS Curr. .

Abstract

Background: Salmonella enterica serovar Typhimurium DT8 is uncommon within the European Union. An increase in this phage type was reported in the summer of 2013 in the States of Jersey.

Methods: A total of 21 human cases with this phage type were microbiologically confirmed. Salmonella isolates from mayonnaise made using raw eggs were also confirmed as being Salmonella Typhimurium DT8. The epidemiological investigations strongly supported a link between mayonnaise consumption and illness. Whole genome sequencing (WGS) was used to retrospectively investigate this outbreak with a view to assess the similarity between the suspect food and the human isolates and to characterise a known point source outbreak to assist in development of algorithms for outbreak detection.

Results: Sequence data showed that the outbreak associated isolates, including the food isolates, formed a tightly clustered monophyletic group, with a maximum pairwise distance of 3 single nucleotide polymorphisms.

Conclusions: WGS data is useful in confirming the causative agent of outbreaks where food and clinical isolates are available. This dataset, comprising a known outbreak, will be useful in the development of automatic algorithms for outbreak detection.

Keywords: Salmonella; duck eggs; food-borne infection; outbreaks; phylogeny.

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Figures

Epidemic curve
Epidemic curve
Epidemic curve of Salmonella Typhimurium DT 8 outbreak
Salmonella Typhimurium
Salmonella Typhimurium
Phylogenetic tree of Salmonella Typhimurium sequenced by PHE until June 2014. Sequence type is denoted by colour. The most common definitive phage types are indicated.
Salmonella Typhimurium DT 8
Salmonella Typhimurium DT 8
Detailed phylogeny of Salmonella Typhimurium DT 8 sequenced by PHE until June 2014. Annotated with Laboratory reference, region of origin, receipt date, isolation source.
See this image and copyright information in PMC

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