Another death has been tied to an outbreak of the C. difficile superbug in Ontario's Niagara region, hospital officials say.

A third patient related to the C. difficile outbreak at a Welland, Ont., hospital died Wednesday afternoon, the Niagara Health System said Thursday.

At least 17 people — mainly elderly — have died in the Niagara region since the outbreak was declared May 28.

Sue Matthews, president and CEO of the Niagara Health System, told reporters that the Ontario Ministry of Health offered a field epidemiologist to help learn more about the outbreak.

The epidemiologist arrived in the region on Thursday afternoon, Matthews said.

A field epidemiologist is helping the outbreak, says Niagara Health System president and CEO Sue Matthews. (CBC) Epidemiologists help collect and analyze data to monitor trends in the outbreak, she said.

Robert Cyrenne, a spokesperson for the Public Health Agency of Canada, said the agency sent a field epidemiologist in response to a request from the Ontario government, acting on behalf of the Niagara Region Public Health.

"Upon request, PHAC regularly assists provinces and territories by providing field epidemiologists," Cyrenne said.

The field epidemiologist is a federally-funded employee based in Toronto and deployed as an additional resource for the outbreak, said Andrew Morrison, a spokesperson for the Ontario Ministry of Health.

The federal agency can also collaborate with provincial and infection-control experts to help prevent, diagnose and analyze strains.

The Niagara region deaths include 10 at St. Catharines General, four at the Greater Niagara General, and three at the Welland Site. Outbreaks were declared June 23 at the Greater Niagara General and Welland sites.

On Wednesday, a fourth health facility in the Niagara region confirmed an outbreak.

The Hotel Dieu Shaver Health and Rehabilitation Centre said four of its patients tested positive within the past few weeks, prompting officials to investigate further and call the outbreak. The other two patients are not part of the outbreak, said the centre, which is not part of the Niagara Health System.

The federal government's help came as Ontario's associate chief medical officer of health, Dr. David Williams, said there were now 10 declared outbreaks in hospitals and one suspected.

The hospitals are in Guelph, St. Catharines, Niagara Falls, Napanee, Toronto, Welland, Orangeville, Hamilton and Mississauga, the Canadian Press reported.

An outbreak, Williams said, could be as few as two cases in a ward, and there are regularly four to six outbreaks happening in the province's hospitals.

Clostridium difficile (C. difficile) causes diarrhea and is one of the most common infections in hospitals and long-term care facilities.

Most cases of C. difficile hit people taking antibiotics. In severe cases, it can cause critical illness and death in elderly or very sick patients.

People most at risk after exposure are typically of advanced age, and with underlying illnesses such as inflammatory bowel disease or immunodeficiency, who are also taking antibiotics.