An outbreak of E. Coli affecting more than 100 UK people could be linked to eating contaminated mixed salad leaves, public health officials say.
To date, 109 people are known to have caught the bug - 102 in England, six in Wales and one in Scotland.
South-west England has been worst hit.
E. coli O157 infection can cause a range of syamptoms, from mild diarrhoea to bloody diarrhoea with severe abdominal pain.
Public Health England says it has triggered heightened surveillance and is carefully monitoring the situation across the UK.
Although the cause of the infection is not absolutely certain, preliminary investigations show many of the people affected ate salad, including rocket leaves, prior to getting sick.
Dr Isabel Oliver, director of PHE's field epidemiology service, said: "At this stage, we are not ruling out other food items as a potential source."
PHE was first alerted to the outbreak at the end of June.
Dr Oliver said people could help protect themselves from possible infection by washing their hands before eating and handling food and by thoroughly washing vegetables and salads that they were preparing to eat.
E. coli O157 is found in the gut and faeces of many animals, particularly cattle, and can contaminate food and water.
Outbreaks of 0157 are rare compared with other food-borne diseases.
Avoiding E. coli infection
Wash hands thoroughly after using the toilet, before and after handling food, and after handling animals
Remove any loose soil before storing vegetables and salads
Wash all vegetables and fruits that will be eaten raw
Store and prepare raw meat and unwashed vegetables away from ready-to-eat foods
Do not prepare raw vegetables with utensils that have also been used for raw meat
Cook all minced meat products, such as burgers and meatballs, thoroughly
People who have been ill should not prepare food for others for at least 48 hours after they have recovered