The outbreak involved 293 cases between May and November 2024.
The UK Health Security Agency (UKHSA) has published a report on a multi-agency investigation into the UK's largest ever Shiga toxin-producing Escherichia coli (STEC) O145 outbreak .
STEC are bacteria which can cause severe food poisoning. People with STEC food poisoning can develop symptoms such as diarrhoea, stomach cramps, vomiting and fever.
The outbreak involved 293 cases between May and November 2024. Almost half of these were admitted to hospital with 11 cases developing complications such as Haemolytic Uraemic Syndrome (a condition which causes kidney failure). There were 2 reported deaths.
In May 2024 UKHSA, Public Health Wales (PHW) and Public Health Scotland (PHS) identified a rapid rise in STEC cases detected through routine disease surveillance.
Whole genome sequencing (WGS) helped experts at UKHSA, PHW and PHS to link affected cases, revealing the scale of the large national outbreak.
UKHSA led the investigation, working with agencies across the 4 UK nations to rapidly identify the cause. This included speaking to people about what they had eaten before becoming unwell and using this information to carry out scientific studies. Pre-packaged sandwiches containing lettuce were identified as the likely cause of the outbreak.
The Food Standards Agency (FSA) and Food Standards Scotland (FSS) coordinated rapid investigations with local authorities and industry partners to trace back and analyse the food chain information provided by cases. This analysis identified 3 common sandwich manufacturers, and UK-grown Apollo lettuce was identified as the likely contaminated ingredient. As a result, the 3 manufacturers undertook a precautionary voluntary recall.
Amy Douglas, Lead Epidemiologist at UKHSA said:
This outbreak demonstrates the vital importance of UK government agencies working together with industry to take decisive action to protect people's health.
It also highlights the crucial role that whole genome sequencing continues to play in disease surveillance, helping us to detect and stop outbreaks more quickly than ever before.
Outbreaks involving fresh produce or ready-to-eat foods are particularly challenging to investigate due to the speed with which they emerge and the high number of cases that we must assess.
By the time we are made aware of an outbreak, often none of the implicated food products are available for testing because they have either been eaten or disposed of, making it difficult to confirm whether they were contaminated.
STEC O145 is a growing threat which is now one of the most common types of Shiga toxin-producing E. coli that we are detecting in our surveillance.
Jacquelyn McCormick, Head of Incidents at the FSA said:
Close collaboration between UK public health and food safety authorities supported by industry partners and local authorities enabled us to quickly investigate and identify the source of the outbreak.
This outbreak demonstrates the complexity of the supply chain and how critical it is for government organisations and the food industry to work together to respond rapidly to food safety concerns and protect public health. The learnings from this are being used to continually improve supply chain controls to ensure food is safe.
Despite extensive investigation it was not possible to confirm how the lettuce had become contaminated.
