An outbreak of Shiga Toxin-producing Escherichia coli Serotype O145:H28 Associated with Domestic Travel and Consumption of Unpasteurized Cheese, UK, 2023

Unpasteurized dairy products carry an inherent risk of being contaminated with STEC and/or other zoonotic gastrointestinal pathogens. In November 2023, a genetically linked and geographically dispersed outbreak of 36 cases of Shiga toxin-producing Escherichia coli (STEC) O145:H28 was detected by the foodborne gastrointestinal pathogens surveillance systems at the UK Health Security Agency, using whole genome sequencing. Reported symptoms included diarrhoea (81%), bloody diarrhoea (65%), vomiting (84%), and 47% of cases were admitted to hospital. A review of the completed enhanced surveillance questionnaires (n = 29) revealed 18 cases reporting travelling first class on trains operated by the same company prior to onset of symptoms, of which 16/18 consumed the same meal which included an unpasteurized cheese. Microbiological testing of the cheese products did not detect the outbreak strain; however, STEC O145:H28 was detected in two bovine fecal samples collected at the dairy farm where the unpasteurized cheese was produced. Analysis of the genome sequencing data confirmed that the 36 human STEC O145 isolates and the two bovine STEC O145 isolates fell within the same 5 SNP single linkage cluster. These findings indicated that the cattle were the likely source of the human infections, via the consumption of contaminated unpasteurized cheese. The food business operator voluntarily recalled the implicated product from sale. Vulnerable groups, such as those who are very young, elderly, pregnant, or immunocompromised, should avoid consuming raw drinking milk and cheeses. Due to advances in clinical molecular diagnostics and enhanced epidemiological surveillance, notifications of foodborne outbreaks of STEC other than serogroups O157 are increasing in the UK. Further improvements in microbiological methods for detecting STEC on the farm and in food are essential for the presale identification of contaminated food items and to reduce the risks to public health.