A national outbreak of Salmonella that has affected 156 people is being investigated, Public Health England said.
The cases in England "occurred in isolated clusters over several months" and have been managed locally, according to the health watchdog.
However, the cases of Salmonella "are now being reassessed as potentially linked under a national investigation," it added.
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The Crown Prosecution Service is to announce its decision later on whether individuals and organisations will face criminal charges.