Health officials are investigating 28 cases of people with diarrhea that may be linked to an outbreak of E. coli connected to a restaurant in Burlington, Ont.

As of Monday, three of the cases have been laboratory confirmed as E. coli O157:H7.

"The focus of our investigation is very much on determining any links with other E. coli outbreaks and, hopefully, establishing the contaminated food or drink," Dr. Bob Nosal, Halton Region's medical officer of health said in a statement.

"Over the course of this week, laboratory testing results may help in this regard."

Halton's health department continues to ask anyone who ate at Johnathan's Family Restaurant, 4121 Fairview St., in Burlington, between Oct. 10 and Oct. 30, and has had symptoms of diarrhea (with or without blood), severe abdominal cramps, nausea/vomiting, and/or fever, to please seek medical attention right away and call Halton Region at 905-825-6000 (toll free 1-866-442-5866).

The restaurant, which voluntarily shut down on Oct. 30, remains closed, and its staff continues to co-operate with the investigation, the health department said.

Also on Monday, Niagara Region said it has investigated a total of 46 cases, including 12 laboratory-confirmed cases of E. coli O157.

Of the 46 cases, 21 are linked to the Little Red Rooster restaurant in Niagara-on-the-Lake, and 20 cases are linked to M.T. Bellies restaurant in Welland. None of the victims is currently in the hospital.

As part of the investigation, Little Red Rooster voluntarily closed on Oct. 24. The M.T. Bellies restaurant also voluntarily closed its kitchen on Oct. 28. The bar remains open.

Initial tests show the E. coli strain in Niagara is different from the strain in North Bay, Ont. As of Oct. 31, North Bay's health unit reported 237 cases, of which 46 were lab confirmed as E. coli O157:H7.

All confirmed cases are linked to the Harvey's North Bay that was closed on Oct. 12, including those from nine other health units in Ontario, Quebec and British Columbia.