Lettuce leaves are thought to be behind the current E.coli outbreak that's left more than 200 people sick and dozens hospitalised in the UK.
It sheds further light on a mystery that's prompted three companies to pull their products from major supermarkets and retail chains over fears of contamination.
The Food Standards Agency (FSA) told Sky News it is "too early to determine" how the lettuce leaves may have become contaminated - but it is "confident" that is the source.
This is highly plausible as these leafy greens offer three possible routes for contamination, notes Professor Jim Monaghan, professor of crop science at Harper Adams University in Shropshire.
E.coli-contaminated manure can end up on lettuce leaves, warns professor
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E.coli "essentially wants to be inside the guts of warm-blooded animals", he told Sky News, but pathogenic strains can be found in between 10-15 percent of dairy herds - which means it contaminates a minority of manure.
E.coli-contaminated manure can end up on lettuce leaves in cases of direct contamination.
In cases of indirect contamination, the bacteria may contaminate soil or water and be transferred to lettuce via this route.
There are precedents for this. After more than 250 people in the UK became sick with E.coli in 2022, the finger was pointed at salad.
It convinced the likes of Doctor Lesley Larkin, head of surveillance, gastrointestinal infections, and food safety at UKHSA to advise the public to "thoroughly wash salad" when preparing food.
A 2019 review of research analysed 35 STEC outbreaks linked to lettuce between 1995 and 2018.
Eight were found to have "poor practice' when processing of the vegetables which 'may have contributed to the outbreak", such as insufficient disinfection.
A further six were linked to animal faeces near the growing fields.
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UK-wide E. coli outbreak has left 67 people hospitalised
Getty ImagesWhat we know so far
All the cases recorded in the outbreak involve Shiga toxin-producing E. coli O145 (Stec).
As of June 11, the total number of confirmed cases is 211. The outbreak is UK-wide.
Of the total, some 147 patients are located in England, 27 in Wales, 35 in Scotland and two in Northern Ireland – although it is believed they were infected while in England.
A total of 67 people have been hospitalised. UKHSA said confirmed cases associated with this outbreak are expected to rise as further samples undergo whole genome sequencing.
Symptoms include diarrhoea, stomach cramps and fever. About 50 percent of cases can develop bloody diarrhoea.
