20a - Shiga toxin–producing Escherichia coli (STEC) O145:H28 outbreak linked to unpasteurised cheese in England and Scotland, 2023
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Background : Shiga toxin-producing Escherichia coli (STEC) represents a major public health concern and non-O157 STEC serogroups have been increasingly associated with outbreaks. In November 2023, national gastrointestinal infections surveillance identified a fast-growing outbreak of STEC O145:H28 in England and Scotland. A multidisciplinary investigation was initiated to identify likely infection vehicle(s) and implement control measures.
Methods : Microbiologically confirmed cases were identified through single-linkage hierarchical clustering based on Single Nucleotide Polymorphisms derived from whole genome sequencing data. Epidemiological investigations identified cases, utilised routine surveillance questionnaires for descriptive analyses and hypothesis generation through a case-case analysis using confirmed non-outbreak cases notified in the same period. Trawling and structured questionnaires were undertaken on exposures of interest. Concurrent food-chain and microbiological investigations were undertaken.
Results : Of 36 confirmed cases, with symptom-onset between 25/07-23/12/2023; 54% were female, median age of 36 years (range 2-81 years). Overall, 65% cases reported bloody diarrhoea, 58% were hospitalised, and one developed Haemolytic Uraemic Syndrome and died. The case-case analysis identified domestic travel (OR=27, 95%CI 7-13, p<0.001), although travel was to and from different destinations. Further investigation identified unpasteurised cheese served by one train operator as the vehicle in 16/17 cases; an additional case had purchased the product from the implicated farm shop. The product was recalled on 24/12/2023. The outbreak strain was detected in two faecal samples collected from the environment at the source farm but not in the cheese, in which another STEC serotype (O109) was identified.
Conclusions Although unpasteurised cheese is a risk factor for STEC infection, the source was detected through the unusual association with domestic travel, precipitating timely implementation of control measures. We recommend clearer labelling of products that pose a risk to public health.