Clostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores. Individual cells are rod-shaped, which gives them their name, from the Greek kloster or spindle. These characteristics traditionally defined the genus, but they are not phylogenetically significant; many species originally classified as Clostridium have been reclassified in other genera.

Clostridium difficile is one of the most common causes of infection of the large bowel (the colon) in the US affecting millions of people yearly. Patients taking antibiotics are at risk of becoming infected with C. difficile. Antibiotics disrupt the normal bacteria of the bowel, allowing C. difficile bacteria to become established in the colon. Many persons infected with C.difficile have no symptoms. These people become carriers of the bacteria and can infect others. In other people, a toxin produced by C. difficile causes diarrhea, abdominal pain, severe inflammation of the colon (colitis), fever, an elevated white blood count, vomiting and dehydration. In severely affected patients, the inner lining of the colon becomes severely inflamed (a condition called pseudomembranous colitis). Rarely, the walls of the colon wear away and holes develop (colon perforation), which can lead to a life-threatening infection of the abdomen.

The number of people hospitalized with a dangerous intestinal superbug has been growing by more than 10,000 cases a year, according to a new study. The germ, resistant to some antibiotics, has become a regular menace in hospitals and nursing homes. The study found it played a role in nearly 300,000 hospitalizations in 2005, more than double the number in 2000.

The infection,  Clostridum difficile, is found in the colon and can cause diarrhea and a more serious intestinal condition known as colitis. It is spread by spores in feces. But the spores are difficult to kill with most conventional household cleaners or antibacterial soap.

C-diff, as it's known, has grown resistant to certain antibiotics that work against other colon bacteria. The result: When patients take those antibiotics, competing bacteria die off and C-diff explodes.

This virulent strain of C-diff was rarely seen before 2000.

There are other factors that play into the rise of C-diff cases as well, including a larger of number of patients who are older and sicker. "And there may be some overuse and inappropriate use of antibiotics," said , a University of Massachusetts researcher and lead author of the study. The Zilberberg study was based on a sample of more than 36 million annual discharges from non-governmental U.S. hospitals. That data was used to generate the study's national estimates.

Using other scientists' estimates, the study concluded that 2.3 percent of the cases in 2004 were fatal - about 5,500 deaths. That was nearly double the percentage of C-diff-related cases that ended in death in 2000. Many of the people who died had other health problems. The study did not try to determine if Clostridium difficile was the main cause of death in each case, Zilberberg said. But earlier research concluded the infection is the underlying cause of thousands of deaths annually, and the problem is getting worse. C-diff has become an acute health concern in Canada, where it was blamed for 260 deaths at seven Ontario hospitals recently, and 2,000 deaths in Quebec since 2002.

The Association for Professionals in Infection Control and Epidemiology is currently working with U.S. hospitals to study prevalence of the infection and what infection control measures seem to work best.