Tests by environmental health officers showed that seven employees at John Barr & Son, an award-winning butcher in Wishaw, had traces of infection.
News of the medical findings emerged as doctors on Teesside announced another outbreak of E.coli food poisoning, which has caused the death of a 90-year-old woman.
Eight pensioners have died so far in the Scottish epidemic, and in Lanarkshire, the worst affected area, the number of suspected cases rose by six yesterday to 296. Of those, 133 are confirmed, an increase of five. Sufferers are being treated at hospitals in Airdrie, Falkirk and Glasgow.
Health officers decided to check all staff working at John Barr & Son after pensioners who ate steak pie supplied by the butcher to a Wishaw church lunch party on 17 November fell ill in large numbers. Initial tests on the pie gravy showed evidence of the E. coli 0157 bacteria.
John Barr & Son, which was voted Scottish Butcher of the Year, employed around three dozen staff working with raw and cooked meat products. Yesterday, the shop was "closed until further notice".
A Lanarkshire Health Board spokesman said: "I can confirm that seven workers have been detected as having the E.coli 0157 infection."
It is not known whether Mr Barr was among them, but it is understood that the workers became infected after the outbreak began and were not carrying the bacteria while still working in the shop.
However, environmental health officers argue that regulations governing the education of food handlers in essential hygiene are inadequate. The law requires only unspecified "training", which could be simple on-the- job skilling.
On Teesside, health officials confirmed two cases of E.coli poisoning, but said they were treating the incident as "isolated" and unconnected with the epidemic in Scotland. One victim, Janet Murray, a great-grandmother from Middlesbrough, died and the other, an elderly man from Stockton, is in hospital.
Dr Ian Guy, public health director with Tees Health Authority, said sporadic cases of this nature arose "all the time" and it was difficult to trace the source of the infection. With large outbreaks, it could be done by taking a detailed food history from victims and pinpointing the source.
While the authorities struggle to identify the causes of fatal food poisoning, the Government is cutting funds for a laboratory leading research into the food bug that has claimed nine lives in little more than a fortnight.
Funding for the Institute of Food Research has been slashed by pounds 2.6m over a two-year period, a move condemned by Labour as "totally irresponsible". The Norwich-based Institute is a leading participant in the UK Predictive Modelling Programme, which is investigating the growth of E.coli 01757:H7. Budget cuts of pounds 800,000 this year will be more than doubled in 1997 to pounds 1.8m.
Gavin Strang, shadow minister for Food, Agriculture and Rural Affairs said: "These massive funding cuts are totally irresponsible. At a time when hundreds of cases have been reported and nine people have died, ministers should be supporting this research, not cutting it back."Reuse content