Health officials have warned the number of victims of an outbreak of the E.coli bug in Leeds could rise.
Nine patients ate meat products from Todd's Pork and Beef Butchers
Fourteen people have so far been affected by the outbreak, with experts saying it could "get very nasty".
A five-year-old girl and an 82-year-old woman are among those struck down by the potentially fatal 0157 strain.
The West Yorkshire Health Protection Unit and Leeds City Council said the source had been confirmed as Todd's Pork and Beef Butchers in Armley.
Dr Martin Schweiger, from the unit, said he had "serious concerns" more people could be taken ill.
'This is ongoing'
"I am very concerned that we have not got to the end of the outbreak yet and I am very concerned that we may still get some very seriously ill people.
"The first case was on 23 June and the oldest lady only came to our attention on Saturday morning.
"Usually you get one or two, then two or three but this is ongoing and could get very nasty."
The public has been warned not to eat or feed to pets any cooked meats or meat products known to have come from the butchers.
The shop, which supplies 18 butchers, cafes and delicatessens in the area, has closed while investigations continue.
A joint statement from Leeds City Council and the Health Protection Agency said nine of the 14 people affected had eaten food from Todd's.
About 12 of those affected were taken to hospital and health bosses said the majority were still receiving treatment.
Dr Schweiger said: "In numerical terms it's small scale but we are dealing with an organism that in other outbreaks has had quite a high death rate.
"Fortunately, nobody so far has died and that's a source of relief. I hope it stays that way."
He praised the shop for agreeing to close while the outbreak was investigated.
People with the bug usually show symptoms between three and eight days after infection, though three-to-four days is more usual.
Dr Mike Gent, Consultant in Communicable Disease Control, said: "All types of E.coli 0157 can cause a range of symptoms from mild diarrhoea to severe bloody diarrhoea.
"A small number of patients, particularly children and older people infected with E.coli can go on to develop further complications."