Foodborne Outbreak of Extended Spectrum Beta-lactamase Producing Shigella sonnei Associated with Contaminated Spring Onions in the United Kingdom

•UKHSA surveillance systems detected an outbreak of ESBL-producing Shigella sonnei in 2021.•Phylogenetic analysis identified Egypt as the geographical origin of the outbreak strain.•Ingredient-level analyses identified imported spring onions as the likely source.•Food chain investigations traced the vehicle back to a single producer in Egypt.•Foodborne transmission of ESBL-producing bacteria is an emerging global health concern. Globalization of the food supply chain has created conditions favorable for emergence and spread of multidrug-resistant (MDR) foodborne pathogens. In November 2021, the UK Health Security Agency detected an outbreak of 17 cases infected with the same strain of MDR extended spectrum beta-lactamase (ESBL)-producing Shigella sonnei. Phylogenetic analysis of whole-genome sequencing data revealed the outbreak was closely related to strains of S. sonnei isolated from travelers returning to the UK from Egypt. None of the outbreak cases reported travel and all 17 cases reported eating food from a restaurant/food outlet in the week prior to symptom onset, of which 11/17 (64.7%) ate at branches of the same national restaurant franchise. All 17 cases were adults and 14/17 (82.4%) were female. Ingredient-level analyses of the meals consumed by the cases identified spring onions as the common ingredient. Food chain investigations revealed that the spring onions served at the implicated restaurants could be traced back to a single Egyptian producer. The foodborne transmission of ESBL-producing bacteria is an emerging global health concern, and concerted action from all stakeholders is required to ensure an effective response to mitigate the risks to public health.