How does E.coli get on to lettuce? Three ways the bacteria can enter the food chain

An E.coli outbreak that has infected more than 200 people has been linked to lettuce.

Although it is "too early to determine" how the lettuce leaves may have become tainted with the bacteria, the Food Standards Agency (FSA) said it is confident it is the source. The FSA has not disclosed if the lettuce was imported or originated on a farm in the UK.

As of June 28, one person in the UK has died from E.coli.

E.coli, short for Escherichia coli, is a type of bacteria that is frequently found in warm-blooded creatures' lower intestines. While most strains of E.coli are not harmful, some can result in severe food poisoning. This is the situation with E.coli (Stec), a bacteria that can cause serious food-bourne illnesses and produces the Shiga toxin.Stec has been found in every case reported in this most recent outbreak.

How does lettuce get E.coli?

Professor Jim Monaghan, a crop science professor at Harper Adams University in Shropshire, said there are three primary ways that lettuce leaves could have become contaminated with E.coli.

According to him, E.coli "essentially wants to be inside the guts of warm-blooded animals" but pathogenic strains are present in 10–15 per cent of dairy herds, meaning that a small percentage of manure is contaminated.

In situations when there is direct contamination, that manure and the E.coli it contains may wind up on lettuce leaves. In situations when there is indirect contamination, the bacteria may enter the soil or water and then find their way to the lettuce.

In order to prevent more cases, farmers are required to wait a minimum of one year before planting lettuce in a field that they have fertilised with manure.To check for the presence of E.coli, they must also test the irrigation water they use.

In order to prevent any water contamination, growers of salad will also risk assess their locations and refrain from planting salad in any places that are likely to flood.

What products have been recalled?

Numerous salads, wraps and sandwiches have been recalled.

Greencore Group

• Aldi Chicken Fajita Triple Wrap

• Amazon BLT Sandwich

• Asda Smoky Beans and Cheddar Cheese Wrap

• Asda Chicken Salad (Sandwich)

• Asda Chicken and Bacon Club (Sandwich)

• Asda Brie, Bacon and Chilli Chutney (Sandwich)

• Asda BLT (Sandwich)

• Asda Vegan No Chicken Caesar Wrap

• Asda Tuna Crunch Sub Roll

• Asda Southern Fried Chicken Wrap

• Asda Southern Fried Chicken Triple Wrap

• Boots BBQ Chicken Wrap

• Boots BLT (Sandwich)

• Boots Cheddar Cheese Ploughman's (Sandwich)

• Boots Chicken and Bacon Caesar Wrap

• Boots Chicken Salad (Sandwich)

• Amazon Chicken Salad Sandwich

• Amazon Prawn Layered Salad

• Boots Chicken Triple (Sandwich)

• Boots Delicious Ham and Cheese Ploughman's (Sandwich)

• Boots Halloumi and Greek Style Salad Wrap

• Boots Ham and Egg Club (Sandwich)

• Boots Mixed Triple (Sandwich)

• Boots Southern Fried Chicken Wrap

• Boots Spicy Bean and Cheese Wrap

• Boots Vegan No Chicken Salad (Sandwich)

• Boots Vegan No Duck and Hoisin Wrap

• Boots Veggie Triple (Sandwich)

Amazon Ploughman's Sandwich

• Co-op Vegan Gro Onion Bhaji (Sandwich)

• Co-op Mexican Style Bean and Cheese Wrap

• Co-op Ham, Cheese and Pickle (Sandwich)

• Co-op Ham and Cheese Wrap

• Co-op Chicken and Bacon Caesar Wrap

• Co-op Bacon, Lettuce and Tomato (Sandwich)

• Morrisons Chicken Salad (Sandwich)

• Morrisons Chicken Salad PFS (Sandwich)

• Morrisons Gluten Free Chicken Salad (Sandwich)

• Morrisons Gluten Free Sandwich Platter

• Amazon Chicken and Bacon Layered Salad

• Sainsbury's Peri Peri Chicken Wrap

• Sainsbury's BBQ Pulled Pork and Red Leicester (Sandwich)

• Sainsbury's Chicken, Bacon and Avocado Focaccia (Sandwich)

• Sainsbury's Greek Style Wrap

• Sainsbury's Jerk Halloumi Wrap

Samworth Brothers Manton Wood

• Tesco Chicken Salad Sandwich

• Tesco Chicken Salad Sub

• The Gym Kitchen Peri Peri Chicken Chilled Wrap

• OneStop Tuna Crunch Sub

• OneStop Chicken Salad Sandwich

• OneStop Hoisin Duck Wrap

• OneStop Chicken, Bacon and Lettuce Sandwich

• Tesco BBQ Chicken Wrap

• Tesco Hoi Sin Duck Wrap

• Tesco The Chicken Club Sandwich

• Tesco Tuna Crunch Sub

• Tesco Spicy Bean Wrap

• Tesco Chicken, Bacon and Lettuce Sandwich

• Tesco Fajita Chicken Wrap

• Tesco Summer Edition Greek Style Chicken Gyros Wrap

How does E.coli spread?

The illness can spread by tainted food, water or contact with other sick individuals or animals.

Depending on the location of the infection, different E.coli symptoms may appear. Some of the main signs of a blood stream infection (bacteraemia) caused by E.coli include fever, chills and shivering; other symptoms include not peeing during the day and increased confusion.

You can reduce the risk of infection by washing your hands regularly and keeping hydrated.

What to do if you suspect you are infected with E.coli

Your doctor or nurse will collect a sample from the infected region (such as a urine sample or a wound swab) if they suspect you may have an E.coli infection. Antibiotics could be administered to you to treat the infection.