Since the last update, 42 cases have been added meaning the total stands at 151 - 144 in England, six in Wales and one in Scotland, with the South West of England particularly affected.
A total of 62 people are known to have received hospital care and two individuals with E. coli O157 infection have died.
UK authorities said they had advised selected wholesalers to stop adding some imported rocket leaves to their mixed salad products.
Whole genome sequencing (WGS) has indicated that the strain involved is likely to be an imported one, possibly from the Mediterranean area.
Italian media said UK companies who import salad from Italy were involved in the investigation.
The European Centre for Disease Prevention and Control (ECDC) told us no other countries have reported being affected.
"We are in contact with the UK authorities and we are monitoring the situation through our Epidemic Intelligence Information System (EPIS) for food- and waterborne diseases."
PHE said it had identified that several ill people ate mixed salad including rocket leaves prior to becoming unwell.
However, the source is not confirmed and remains under investigation with other food items not being ruled out.
Food samples negative
Dr Isabel Oliver, director of PHE’s field epidemiology service, said it is working with the Food Standards Agency (FSA) to trace, sample and test salad products grown in the UK and other parts of Europe.
“All food sample results to date have been negative for E. coli O157, but it’s important to be aware that where food has been contaminated with E. coli O157, it is not always possible to identify the bacteria on food testing.
“As an additional precautionary measure, we have advised a small number of wholesalers to cease adding some imported rocket leaves to their mixed salad products pending further investigations.”
PHE has heightened surveillance for the strain of E. coli and is monitoring the reporting of cases across the country as well as creating a national outbreak control team.
The strain involved has been identified as phage type (PT) 34.
The FSA said the outbreak has been linked to eating mixed salad leaves, including rocket leaves, however a specific food source has not been confirmed.
“As a precaution, the FSA is reminding people of the importance of good hand and food hygiene practices. All vegetables, including salads, intended to be eaten raw should be thoroughly washed unless they are specifically labelled ‘ready to eat’.”