The UK is dealing with an alarming outbreak of a rare strain of E. Coli, which has already affected more than 200 people.
The source of this diarrhoea-causing bug is believed to be contaminated salad leaves, particularly a type of butterhead lettuce known as Apollo.
Despite efforts by food safety chiefs, the exact method of contamination remains unknown.
In response to the outbreak, more than 60 sandwiches, wraps, and salads sold in 11 major retailers have been issued with ‘do not eat’ alerts.
These products are feared to contain Shiga toxin-producing E. Coli (STEC), a highly infectious strain that can cause severe illness.
Salad leaves have a notorious history of being linked to E. Coli outbreaks.
Research suggests that leafy greens are responsible for half of all E.Coli incidents.
Experts attribute this to the texture of lettuce, which can harbour bacteria more easily, and the fact that salads are typically consumed raw, bypassing the cooking process that would normally kill harmful pathogens.
Professor Paul Hunter, an infectious diseases expert from the University of East Anglia, told MailOnline: “Watering during growth allows potentially contaminated water to rest on the lettuce leaf.
“The rough and waxy surface of the leaf makes it difficult to wash off E. coli.
“The main risk comes from bacteria attached to the leaf surface, as opposed to other vegetables which are either peeled or cooked before eating.”
Professor Hunter’s research, including a 2019 review, highlighted the frequent occurrence of E. Coli outbreaks linked to lettuce.
The review found that poor processing practices, such as insufficient disinfection, and proximity to animal faeces were common contributing factors.
Bagged lettuce, already prepared for consumption, was often implicated.
To get rid of the risk of contamination, experts recommend thoroughly washing all salad leaves by immersing them in cold water.
Proper storage is also crucial, keeping salad bags in the fridge at temperatures below four degrees Celsius can significantly slow bacterial growth.
Recent weather conditions in the UK have also allegedly exacerbated the problem.
The combination of wet and warm weather creates an ideal environment for E. Coli to thrive.
Professor Eileen Wall from Scotland’s Rural College (SRUC) said that rain can cause contaminated water to splash onto lettuce leaves, while warmth promotes bacterial proliferation.
Professor Nicola Holden, also from SRUC, added that high humidity within the leaf canopy during rainy weather further supports the spread of STEC.
The UK Health Security Agency (UKHSA) typically records around 1,500 STEC infections annually.
However, from May 25 to June 11, there have already been 211 confirmed cases of the strain linked to the outbreak.
The majority of cases are in England, with significant numbers also reported in Wales and Scotland.
At least 67 people have been hospitalised, including children as young as two, though most victims are young adults.