As many as 93 people in Ontario could be afflicted with a potentially deadly strain of E. coli linked to a popular fast-food restaurant, health authorities reported Thursday.

Laboratory tests have confirmed 15 cases of poisoning due to E coli O157:H7, with 78 others under investigation, stemming from a Harvey's restaurant in North Bay, Ont.

Dr. Catherine Whiting, the area's medical officer of health, said in an interview the outbreak has spread beyond North Bay, with one confirmed case in Sudbury, Ont.

Four other cases - including one in eastern Ontario - may also be linked to the outbreak, she said.

Victims range in age from five to 84 years old, with nine reported to be in hospital and the rest recovering at home.

"It's sad to have people getting ill," Whiting said.

However, no cases of kidney failure or other serious complications had been reported.

The North Bay Parry Sound District Health Unit said the actual source of contamination at the restaurant is not yet known.

Whiting said 75 people who fell ill reported eating hamburgers at the restaurant, suggesting either the meat, toppings or condiments could have been the culprit.

"It takes further analysis ... to see what truly ends up being the item of suspicion," Whiting said.

Rick McNabb, president of Harvey's Canada, said tests should be able to pinpoint the contamination source by early next week, and the information will be made public.

However, he said there is no reason for the public to fear a more widespread problem or that other outlets in the 290-restaurant chain pose any health risk.

"This is clearly a difficult time and obviously we feel terrible about what has happened," McNabb said in an interview.

"(But) this is an isolated event that is specific to this location."

The restaurant was closed Sunday evening and is co-operating with the outbreak investigation. A field epidemiologist with the Public Health Agency of Canada has also been helping out.

"All the health units are on alert to identify cases," said Health Ministry spokesman Andrew Morrison.

The typical incubation period for E. coli is three or four days - but could be as long as nine or 10 days - indicating more people could still fall ill, Whiting said.

"I am anticipating more cases over the next couple of days," she said.

"I am hoping, based on the incubation period and closure of the facility, that we would then begin to see a decline, but there are often secondary cases."

The bacterial strain is the same one that afflicted the town of Walkerton, Ont., in May 2000, when seven people died and about 2,500 others fell ill.

In that case, the outbreak was traced to contaminated municipal tap water, but that's been ruled out in the North Bay case.

Coincidentally, Dr. Bill Clark, who headed a long-term health study of the Walkerton victims, was giving his final report to the community Thursday.

Poison from the hardy E. coli 0157:H7 bacterium damages small blood vessels, including those in the lining of the intestines, resulting in characteristic bloody diarrhea.

The very young and frail elderly are especially susceptible to kidney failure or even strokes resulting from infection.

Other symptoms of infection include stomach cramps, nausea and possibly a fever.

Treatment is essentially supportive - giving patients fluids to prevent dehydration.

Because E. coli bacteria are easily spread, health officials urge especially careful handwashing and other sound hygiene practices when dealing with suspected cases of infection.

One suspected case in the North Bay outbreak may be the result of an infected person passing on the contamination.