Four people have died as a C. difficile bacterial infection spreads in Cape Breton hospitals.

The Cape Breton District Health Authority says 21 patients have tested positive for the bacteria, including 13 at the hospital in Sydney and seven in Glace Bay.

Clostridium difficile usually occurs in patients who take regular antibiotics. The bacteria grow in the large bowel and cause diarrhea and serious intestinal conditions. Very sick patients are most at risk.

Dr. Shoaib Ansari, the district's infectious disease specialist, said the infection is proving difficult to treat, so there are more relapses and more severe cases.

"Usually it takes up to 10 to 14 days of antibiotics to cure this infection. But the problem we are having with this particular strain is that even if we are able to get our patients better, once they come off treatment after a week or so the infection comes back," he said.

Health officials say the four people who died in the past few weeks were all sick and elderly.

Ansari said it's likely other seriously ill patients will die before the infection is under control.

Kim MacNeil's mother was admitted to the hospital in Sydney two weeks ago and now has C. difficile.

"It's very discouraging," MacNeil said. "We were hoping that everything was going to start falling into place as far as her healing and getting better and then this here is thrown at her. It's just not right. But what can you do?"

Spores from C. difficile bacteria can spread if people with diarrhea touch something without washing their hands.

To prevent the bacteria from spreading further, visitor restrictions are in place at all hospitals, community health centres and continuing-care facilities in the region.

Children under 12 and anyone with an illness are banned. Those allowed in must clean their hands with soap and warm water. Some will have to wear gloves and a gown.

Since 2005, there have been a rising number of C. difficile-related cases of severe diarrhea in Canadian hospitals that persist for months despite repeated treatments.