Four children and an adult are in hospital following an E.coli outbreak, health officials have said.
A total of 12 people have been affected so far, with four cases being reported in the last 24 hours.
A definite source has not yet been identified but many of those affected were known to have eaten pre-cooked meats or savoury products supplied by Robinson's Butchers and Caterers, which has shops in Wingate in County Durham and Billingham in Teesside.
Officials from Public Health England and environmental health teams from County Durham and Stockton councils are investigating all possible sources of the outbreak.
They have urged people to throw out any pre-cooked meats or savouries bought since June 25 from Robinson's in Wingate and Billingham, including any they may have in the freezer.
Consultant in health protection and chair of the outbreak control team Dr Deb Wilson said: "The source of this outbreak is not yet known. However, many of the affected people are known to have eaten cooked meat products bought or supplied by Robinson's butcher shops in either Wingate or Billingham.
"The owner and staff of Robinson's Butchers and Caterers are co-operating fully with the investigation.
"They have conducted a deep clean of both premises and discarded all ready to eat food prepared before 16 July 2015.
"E.coli O157 infection can cause severe stomach pain, bloody diarrhoea and, more rarely, kidney failure in children."