An E. coli outbreak in North Bay, Ont., has spread to include 93 confirmed and suspected cases, a number expected to grow.

The city's medical officer of health said Thursday that 15 people have tested positive for the potentially lethal strain of E. coli O157:H7 and 78 more cases are under investigation. The average incubation period for E. coli is three or four days.

"At the current time we have no one that has been ill enough to be in an intensive care unit," Dr. Catherine Whiting told CBC. "We are also cognizant of one of the complications of an infection with E. coli O157:H7 is that you can have a condition called hemolytic uremic syndrome, or a type of kidney failure. So we are definitely in surveillance for that."

The strain is the same as the one that killed seven people in the town of Walkerton, Ont., in May 2000 after an outbreak traced to contaminated municipal tap water.

Health officials in North Bay said the outbreak in the city appears to have originated at a Harvey's restaurant, although the source of contamination is not yet known.

The restaurant was closed Sunday evening.

With files from the Canadian Press