It was discovered last night that cooked cold meats from the deli counters at the two Morrisons supermarkets linked to the case were also used in customer cafés and staff canteens at the sites.
The outbreak control teams of NHS Greater Glasgow and Clyde say that the deli at Paisley's Lonend store had supplied the tainted ham for the preparation of a limited number of pre-packed sandwiches. The other affected branch is at Falside Road.
A spokeswoman of the outbreak team has confirmed that no cases of E. coli 0157 have yet been linked with these sources. She added there had been no new confirmed cases relating to the outbreak.
In spite of this, officials emphasize that anyone who has bought ham sandwiches from the Lonend outlet or eaten sliced cold meats from the café or staff canteen "in the past couple of weeks" and who is now feeling unwell should contact their GP or NHS 24.
Following the recent outbreak of E. coli poisoning three persons are still being treated in hospital.
Margaret Rowan, a 66-year-old disabled woman, died on Monday in Paisley's Royal Alexandra Hospital after becoming ill last Friday. Her 72-year-old husband, named locally as Stephen, is in a "serious but stable" condition in the Victoria Infirmary in Glasgow. A 71-year-old woman is "unwell but improving" at the Royal Alexandra Hospital. A 70-year-old Paisley woman remains stable in hospital in Ireland.
Officials gave that four other people who had contracted E coli "continue to recover well at home".
Meanwhile, environmental health officers are investigating the 12 suppliers, which provide cold cooked meat to Morrisons.
Officials have taken samples and swabs from the chain's two branches in Paisley, and they have been sent for analysis.
Officials are also interviewing all Morrisons staff that may have had contact with the two delicatessen counters where the meat was bought.
Cranswick Country Foods, one supplier to the delis, said yesterday it was working with environmental health officers. Three years back, some batches of the firm's cooked lamb, which was distributed to Morrisons' delis, were recalled after testing positive for salmonella.
Says Adam Couch, a spokesman for the firm: "We're not the exclusive supplier of deli meats to Morrisons, but we do supply the chain with a wide range of products for delis.
"We've been co-operating with the local environmental health officers, and we've carried out rigorous microbiological tests. We're satisfied with all our records but we'll assist Morrisons with the investigation."
The outbreak team spokeswoman said a number of other confirmed E. coli 0157 cases had been investigated in Scotland and England, though so far none had been linked to the outbreak.
Symptoms of E coli infection include stomach cramps, diarrhea - often bloody - nausea and fever.
Meanwhile, Morrisons was warned yesterday its reputation could be damaged unless it takes action to reassure consumers.
Grant Organ, of crisis management firm Marsh was quoted: "Reputation or 'consumer confidence' can be greatly affected with any crisis, but none more so where food issues are concerned.
"Particularly in the increasingly competitive food retail sector, the way in which a company is perceived to deal with a crisis will make or break their reputation. Once damage to a firm's reputation and brand have incurred, a long, hard struggle to recover often ensues."
Mr. Organ opined that Morrisons should take steps such as providing information in stores and on its website. He said: "Press reports would suggest this process hasn't happened as smoothly as it could, which should be of concern to the firm."
As of now, Morrisons has declined to comment.