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Epidemiol Infect. 2017 Jan;145(2):289-298. Epub 2016 Oct 26.

Prospective use of whole genome sequencing (WGS) detected a multi-country outbreak of Salmonella Enteritidis.

Author information

Field Epidemiology Services,Public Health England,UK.
Gastrointestinal Bacteria Reference Unit,Public Health England,Colindale,UK.
Instituto de Salud Carlos III,Laboratorio de Referencia e Investigación en Enfermedades Bacterianas Transmitidas por Agua y Alimentos. Centro Nacional de Microbiología,Madrid,Spain.
Food Standards Agency,UK.
Department of Infectious Disease Epidemiology,Imperial College London,UK.
Food Water and Environmental Microbiology Laboratory,Public Health England,UK.
NIHR Health Protection Research Unit in Gastrointestinal Infections,University of Liverpool,UK.
Health Protection Scotland, Gastrointestinal Disease and Zoonoses,UK.
Scottish Microbiology Reference Laboratories,Glasgow,UK.


Since April 2015, whole genome sequencing (WGS) has been the routine test for Salmonella identification, surveillance and outbreak investigation at the national reference laboratory in England and Wales. In May 2015, an outbreak of Salmonella Enteritidis cases was detected using WGS data and investigated. UK cases were interviewed to obtain a food history and links between suppliers were mapped to produce a food chain network for chicken eggs. The association between the food chain network and the phylogeny was explored using a network comparison approach. Food and environmental samples were taken from premises linked to cases and tested for Salmonella. Within the outbreak single nucleotide polymorphism defined cluster, 136 cases were identified in the UK and 18 in Spain. One isolate from a food containing chicken eggs was within the outbreak cluster. There was a significant association between the chicken egg food chain of UK cases and phylogeny of outbreak isolates. This is the first published Salmonella outbreak to be prospectively detected using WGS. This outbreak in the UK was linked with contemporaneous cases in Spain by WGS. We conclude that UK and Spanish cases were exposed to a common source of Salmonella-contaminated chicken eggs.


Epidemiology; outbreak; salmonellosis; traceback; whole genome sequencing

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