According to a spokesman for Tayside Health Board, 13 people have now been confirmed as suffering from the bacteria, and there are a further 41 suspected cases.
Tayside Health Board said there were four people in hospital last night, all making satisfactory progress. Of the con- firmed cases, eight men, three women and two children are ill
The announcement followed a meeting of the outbreak control team, formed after the infection came to light at the Isle of Skye Hotel in Perth.
The hotel's owners, Bass Taverns, said the source of the outbreak remained a mystery. The hotel's kitchens have been cleaned twice and the restaurant has remained closed since the individuals fell ill.
A spokesman for the health board said: "The public health department is liaising with colleagues throughout the country to ensure any suspected cases are identified and investigated.
"Environmental health officers are engaged in tracing the food histories of the people affected to try and identify any common source."
People involved come from as far afield as Easter Ross in the Highlands and England, making this a "complex task."
The spokesman said two of the victims were being treated in Perth Royal Infirmary and the other two at Kings Cross Hospital, in Dundee.
Labour yesterday demanded that Scottish Secretary Michael Forsyth give evidence at the fatal accident inquiry into the deaths of victims of the E.coli food poisoning outbreak in central Scotland.
Shadow Scottish Secretary George Robertson said Mr Forsyth and health minister Lord James Douglas-Hamilton would have to give a "full and frank account" of their role in handling the crisis.
Labour resumed its onslaught on the Government following Tuesday's publication of the Pennington report into the outbreak, which claimed 18 lives in the Lanarkshire and Forth Valley health board areas.
Mr Robertson said the ministers' appearance at the inquiry was the only way to restore public confidence in food safety, which began in November.
"The Pennington report catalogues the hands-off, slackly regulated, profits-first attitude to food safety which has been the hallmark of this Government," he said.
"This report could not, because of legal constraints, address some of the outstanding questions on the whole E.coli tragedy. The role of ministers in the early handling of these events is still shrouded in sinister mystery."
He claimed the Scottish Office issued a Food Hazard Warning on 27 November with a list of affected outlets but restricted its distribution to environmental health departments with instructions that it should not be released to the public.
"The buck stops with the Secretary of State and the Minister for State and we have a right to know if they will testify under oath," he said.
The Scottish Conservatives refused to comment on Mr Robertson's demand, claiming it was a governmental matter.
Meanwhile, a Scottish Office spokesman said it was up to the sheriff in charge of the fatal accident inquiry to decide who is called to give evidence.