E coli Outbreak Linked to Contaminated Lettuce

Timeline of events and cascading risk pathway and potential data sources, the United Kingdom, August–October 2022.

Image credit: Eurosurveillance

Eurosurveillance reports a significant outbreak of Shiga-toxin producing Escherichia coli (STEC) O157 in the UK, with contaminated lettuce identified as the likely source. The outbreak from September 2022 resulted in 259 confirmed cases of gastrointestinal illness and highlighted the growing impact of climate change on food safety.

The study identified the likely source of the infected lettuce as Grower X. Researchers suggest that heavy rainfall and flooding may have facilitated the transfer of STEC from animal feces to lettuce crops, highlighting how climate-related factors can influence food contamination.

The investigation combined whole genome sequencing (WGS), epidemiological investigations, food chain analysis, and innovative geospatial methods to trace the outbreak’s origin. WGS confirmed the 259 cases with illness onset between August 5 and October 12, 2022, with 75 individuals requiring hospitalization.

“The outbreak was detected following a rapid and unexpected increase in laboratory notifications of presumed STEC isolates, confirmed by genome sequencing to be STEC O157 with a specific genetic profile defined at the 5-SNP level as the outbreak strain,” according to investigations.

E coli (STEC) O157 is a food-borne pathogen that causes gastrointestinal illness in humans, with ruminants being the main reservoir. Heavy rainfall has been associated with increased STEC outbreaks.

“A combination of phylogenetic analyses, traditional epidemiological analyses, food chain investigations with a novel approach using data on upstream climate hazards led to the conclusion that domestically grown (UK) lettuce contaminated during an adverse flooding event, was the most plausible vehicle of infection,” according to investigators. “The analysis of climate-related factors independently confirmed the location of Grower X identified as the likely implicated producer of salad leaves in this outbreak.”

While the study lacked microbiological sampling from animal reservoirs, products, or the environment, it cannot definitively confirm a zoonotic origin for the outbreak. However, the outbreak strain, prevalent in UK sheep since the 1980s and associated with sheep near Grower X, suggests a domestic ovine reservoir is the most likely source. Previous links to lamb meat products and environmental contamination further support this hypothesis.

The study underscores the increasing risks posed by climate change, as more intense rainfall events may heighten the likelihood of such outbreaks in the future. It also highlights the value of combining One Health approaches with advanced analytical techniques to understand and address food safety issues, ultimately improving public health preparedness and response.

References

1. Cunningham N, Jenkins C, Williams S, et. al. An outbreak of Shiga toxin-producing Escherichia coli (STEC) O157:H7 associated with contaminated lettuce and the cascading risks from climate change, the United Kingdom, August to September 2022. Euro Surveill. 2024;29(36):pii=2400161. Published September 11, 2024. https://doi.org/10.2807/1560-7917.ES.2024.29.36.2400161

2. Study on E. coli outbreak in the UK demonstrates increasing impact of climate change on public health and food security. EurekAlert. September 5, 2024. Accessed September 11, 2024. https://www.eurekalert.org/news-releases/1056930