Clostridium difficile is a type of bacteria that causes diarrhea, inflammation of the colon and abdominal pain. It is contagious to others through the fecal-oral route. Fecal matter contains the bacteria, and is spread typically when people practice poor hygiene when eating or touching contaminated surfaces. Read what the Mayo Clinic has to say about C. difficile: http://www.cdiffsupport.com/aboutcdiff.html.
Clostridium difficile is an infection which is treated with antibiotics. If treatment is successful, it will not longer be contagious after those antibiotics. This is if the stool does not test positive for the bacteria.