Early investigations claim the infection, in the Paisley area of Glasgow, could have come from cold meat bought at Morrisons stores at Lonend and Falside Road.
The Public Health Protection Unit (PHPU) at NHS Greater Glasgow and Clyde was investigating the outbreak and said currently there were two family clusters and two isolated cases.
In the first family, a 66 year-old woman has died as a result of contracting the infection. Her husband, 72, was seriously ill in hospital.
In the second family, two women aged 23 and 45 and a man aged 46 were all recovering well at home.
One of the single cases was a 71 year-old woman who is unwell but stable in the Royal Alexandra Hospital in Paisley.
The second single case is a woman aged 86 who was recovering at home.
The PHPU is working closely with Environmental Health colleagues from Renfrewshire Council, the Food Standards Agency and Health Protection Scotland to identify the source of the infection.
At present, it said there was no conclusive evidence yet, but initial investigations indicated there may possibly be a link to the consumption of some sliced cold meats bought locally from the delicatessen counters of two Morrisons' supermarkets in Paisley, the Lonend store and the Falside Road store.
Further investigations are continuing, but, as a precaution, sliced cold meats have been withdrawn from the two stores and the PHPU was advising consumers who have bought sliced cold meat from these delicatessen counters not to consume them.
There is no evidence to suggest that pre-packed cooked meats purchased from the stores or other food purchased from the delicatessen counters are implicated, it added.
Morrisons was reported to be cooperating fully with the Outbreak Control Team and this morning Environmental Health officers from Renfrewshire Council are carrying out further investigations at the two stores on behalf of the Outbreak Control Team.
Dr Syed Ahmed, chair of the Outbreak Control Team, said: "We were dealing with two apparently unrelated families with confirmed O157 on Friday.
"On Monday , two further single cases from the same area of Paisley were notified to Public Health."
A statement from Morrisons said: "We are deeply saddened to hear an elderly patient has died and two other people are seriously ill in hospital.
"We are currently working closely with the authorities and although the full facts are not yet known, we have, as a precautionary measure, withdrawn sliced cold meat from sale at the delicatessen counters of the two stores."