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UK-grown Apollo leaf lettuce used in pre-packaged sandwiches was the likely source of the UK’s largest recorded STEC O145 E. coli outbreak, according to a newly published report. However, after extensive enquiries, investigators have not been able to confirm how the lettuce became contaminated.
The investigation covered cases recorded between May and November last year, when 293 people were affected by the bacteria, which can cause severe food poisoning. Reported symptoms included diarrhoea, stomach cramps, vomiting and fever, and two people died.
Almost half of those infected were admitted to hospital, while 11 people developed complications including Haemolytic Uraemic Syndrome, a condition that causes kidney failure.
How investigators traced the outbreak
The rapid rise in STEC O145 cases was detected through routine disease surveillance, triggering a multi-agency investigation across all four UK nations.
Analysis of the food histories of those who became ill, alongside scientific studies, enabled agencies to identify three sandwich manufacturers in common among cases. The most frequently reported sandwich types were bacon, lettuce and tomato, and chicken salad sandwiches. Investigators then assessed that UK-grown Apollo lettuce was the most likely contaminated ingredient.
Recalls and the role of genome sequencing
Following the findings, the three manufacturers carried out a precautionary voluntary recall.
Whole genome sequencing was used to link cases and establish the scale of the national outbreak. Amy Douglas, lead epidemiologist at the UK Health Security Agency, said the incident underlined how whole genome sequencing can help authorities detect and stop outbreaks faster than in the past.
Why fresh-produce outbreaks can be hard to prove
Ms Douglas said outbreaks involving fresh produce or ready-to-eat foods can be particularly difficult to investigate because they can emerge quickly and involve large numbers of cases.
She said that by the time an outbreak is identified, suspected products are often unavailable for testing because they have been eaten or thrown away, making it hard to confirm contamination.
In the report, STEC O145 was described by Ms Douglas as a “growing threat” and among the most common types of Shiga toxin-producing E. coli currently being detected. Authorities have also reported a significant rise in UK E. coli cases in recent years.
Further information referenced in the coverage included: https://www.gov.uk/government/news/ukhsa-publishes-report-into-uks-largest-stec-outbreak, https://news.sky.com/story/e-coli-outbreak-what-are-the-warning-signs-of-infection-13149471, and https://news.sky.com/story/e-coli-infections-rise-by-26-as-source-of-outbreaks-and-most-vulnerable-age-groups-revealed-13404342.
Other links appearing alongside the report were: https://news.sky.com/story/meghan-contacts-estranged-father-thomas-markle-in-philippines-hospital-13481717 and https://news.sky.com/story/is-this-what-the-beginning-of-a-war-looks-like-how-the-us-threat-around-venezuela-is-shaping-up-13479426.
Sky News also promoted its WhatsApp channel link: https://whatsapp.com/channel/0029Va868Fv8vd1UsF99tP1u.
