A "disease detective" has been dispatched from Ottawa to help investigate the outbreak of the deadly superbug C. difficile in hospitals in southern Ontario, specifically the Niagara region.

A field epidemiologist with the Public Health Agency of Canada has been asked investigated after the bug hit as many as 10 hospitals.

At least four hospitals in the Niagara Region and one in Guelph, Ont., have been affected by the outbreak. A number of emergency rooms in nearby towns have also been closed to prevent further spread.

Sixteen people in the region have died since the outbreak began in late May.

Hospitals in Napanee, Toronto, Hamilton and Mississauga have also declared cases of C. difficile.

Dr. Doug Sider, acting director of infectious disease prevention and control for Public Health Ontario, points out that C. difficile has become a common pathogen in hospitals in recent years that.

He says investigators are still trying to understand why there's been an upswing of cases in Niagara.

"Is it part of just the normal variation on a month-to-month basis, or are there other factors that are going on?" he told CTV News Channel Thursday.

He said investigators need to find out if there are particular problems with hospital infection prevention methods -- or if the sudden upswing of cases simply is the result of more vigilant surveillance.

Ontario Health Minister Deb Matthews said it is common for epidemiologists to be called in to investigate and says the crisis is not escalating.

"There is nothing unusual happening. This happens in hospitals across the province from time to time," she told reporters in Toronto.

"It's not desirable. We're fighting very hard to prevent it from happening. We track it so closely now that we see it earlier than we ever have seen it before and take appropriate steps."

The strain of bacteria involved, Clostridium difficile, can cause severe diarrhea in vulnerable patients. Hospital patients who have had to take antibiotics are also at greater risk of infection, as are the elderly in nursing homes.

The bacteria are typically spread in hospitals through contact with bodily fluids.

Full-blown outbreaks can usually be avoided if staff recognize an emerging outbreak early and step up measures to prevent further spread, such as more frequent hand-washing.

On Wednesday, about 100 protesters took to the streets to complain about the state of cleanliness at regional health centres.

Sider says the hospitals involved have already done "a ton of work" on their own to investigate the outbreak, and have been working with the regional infection control network as well.

He says the PHAC field epidemiologist will help to make sure that the hospitals' data systems are working as they should to track infections, and report them properly both to local authorities and to the public.

With files from The Canadian Press