An outbreak of food-borne infection linked to a restaurant was reported to the UK Health Security Agency (UKHSA) East of England Health Protection Team (HPT) in early April 2023. Whole genome sequencing (WGS) results indicated Salmonella Enteritidis infection, with all cases in a 5-single nucleotide polymorphism (SNP) cluster falling into a wider genomically diverse 10-SNP cluster investigated in several countries. We identified additional cases in the 5-SNP cluster with no known links to the restaurant, and historical cases reported since July 2022.
Our investigations aimed to define common exposures for cases in the 5-SNP cluster to determine the likely source of infection and implement control measures.
A confirmed case was defined as a person with laboratory-confirmed S. Enteritidis infection belonging to the 5-SNP cluster 1.2.3.18.180.7268.% [1] in England since 1 March 2023. A probable case was defined as a person with gastroenteritis or confirmed Salmonella spp. infection in England who dined at the restaurant of interest from 1 March to 1 April 2023. Confirmed cases were further categorised as having known, unknown or no exposure to the restaurant.
In early April 2023, UKHSA was notified via Accident and Emergency doctors, general practitioners, and a local authority environmental health (EH) department of multiple cases of gastroenteritis following food consumption at a restaurant, with attendance or take-away dates in late March. We identified S. Enteritidis as the causative organism. Salmonella isolates are routinely sent to the UKHSA Gastrointestinal Bacteria reference unit (GBRU) for sequencing [2]. The outbreak cases were confirmed to be within a 5-SNP cluster defined at UKHSA as 1.2.3.18.180.7268.% matching the Enterobase cgMLST hierarchical cluster HC2_316378 [3], falling into a wider genomically diverse cluster 1.2.3.18.180.%/HC5_2301 that is subject to several national and international investigations.
Cases identified through initial case notifications were interviewed using generic food history questionnaires; for cases notified since 2 May 2023, a bespoke menu-based questionnaire was used. Early cases were re-interviewed with the bespoke questionnaire completed by telephone or online. Additional cases identified through WGS were contacted to establish whether they were linked to the restaurant, and if so, asked to complete the bespoke questionnaire by telephone or online. Cases who did not reveal exposure to the restaurant completed a modified Salmonella trawling questionnaire focussed on poultry products.
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