More than 200 cases of E.coli have been detected in the UK as a result of a single outbreak.
At least 67 people have been admitted to hospital - and the UK Health Security Agency (UKHSA) has warned cases are likely to rise.
Most infections are in young adults - with children as young as two and adults as old as 79 among the cases.
Here, we will explain everything you need to know.
What is E.coli?
Short for Escherichia coli, E.coli is a bacteria that is commonly found in the lower intestine of warm-blooded organisms.
Most E.coli strains are harmless but some can cause serious food poisoning.
That is the case with Shiga toxin-producing E.coli (Stec), a bacterium that can cause severe foodborne disease.
All the cases recorded in this latest outbreak contain Stec.
There are typically about 1,500 cases of Stec over a full year in the UK, according to the UKHSA.
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What has happened?
Earlier this month, the UKHSA said the recent cases were linked to a single outbreak.
Because of the "wide geographic spread of cases", the UKHSA believes it is linked to nationally distributed food items.
As of 11 June, 147 patients are based in England, 27 in Wales, 35 in Scotland and two in Northern Ireland.
What food is affected?
On 14 June, two sandwich manufacturers that supply UK supermarkets - Greencore and Samworth Brothers Manton Wood - recalled products because of an E.coli risk.
Products from Boots, Asda, Tesco, Co-op, Aldi, Sainsbury's and Amazon were affected.
You can find a list of products included in those recalls here.
On 17 June, a company called THIS announced a recall for a vegan chicken and bacon wrap only sold in WHSmith.
All three recalls have been described as a precautionary step, with the Food Standards Agency narrowing the source of the outbreak "to a small number of salad leaf products that have been used in sandwiches, wraps, subs and rolls".
I bought one of these products. What should I do?
The UKHSA is urging anyone who has bought a now-recalled item not to eat it.
Instead, they should return it to the store where it was purchased from for a refund.
How does Stec spread?
Primary sources of Stec outbreaks are raw or undercooked ground meat products, raw milk, and faecal contamination of vegetables.
It is often transmitted by eating contaminated food but can also be spread by close contact with an infected person, as well as direct contact with an infected animal or its environment.
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What are the symptoms?
The main symptoms are stomach cramps, severe and sometimes bloody diarrhoea.
Some people may only get mild diarrhoea, or even show no symptoms at all.
Symptoms can last up to two weeks in cases without complications.
For some patients, mainly children, it can cause haemolytic uraemic syndrome (HUS) - a serious life-threatening condition resulting in kidney failure.
In an information leaflet, the UKHSA says that HUS may occur up to two weeks after the start of the diarrhoea.
It adds: "If your symptoms do not go away or you develop easy bruising, feel you are passing less urine than usual or your urine is pink/brown in colour, please urgently seek medical advice as these symptoms could indicate the start of HUS and you may need further tests."
A small proportion of adults may develop a similar condition called thrombotic thrombocytopenic purpura (TTP).
Virologists have warned the illness can be much worse in young children, elderly people, and those with underlying conditions in their immune system.
Parents concerned about a baby under 12 months are being advised to call 111 or contact their GP surgery - especially if the child stops breast or bottle feeding, or shows signs of dehydration.
How is it treated?
There is no specific treatment for a Stec infection and it will usually clear itself within a week. It is important to drink plenty of fluids as diarrhoea can lead to dehydration.
Antibiotics are not recommended and are likely to increase the risk of getting complications such as HUS.
E.coli health advice
To reduce the risk of catching and spreading the disease, the UKHSA has advised:
• Regularly washing your hands with warm water and soap - alcohol gels do not kill all of the bugs that cause diarrhoeal illness
• Following food hygiene measures such as washing fruit and vegetables and cooking food properly
• Not preparing food for others if you have diarrhoea and vomiting
• Avoiding visiting people in hospitals or care homes to prevent passing on the infection
• Not returning to work, school or nursery until 48 hours after symptoms have stopped
Have there been outbreaks like this in the UK before?
There were 27 Stec cases recorded during an outbreak in June last year that was linked to minced beef products.
In 2022, there was an outbreak that caused more than 259 people to get ill between August and the end of October. The agencies investigating suggested a salad had possibly caused the cases.
It's not uncommon for products to be recalled over fears of outbreaks, as was the case with five cheese products last December.
