This is a prospective, cross-sectional, and observational study. The patients with nosocomial diarrhea whose stool samples are sent for stool examination and Clostridium difficile toxin by their treating physicians will be recruited. Their leftover stool samples will be kept at

• 80 c and will be measured for calprotectin level at the end of study. The patients will be treated by their treating physicians. They will be classified into 2 groups - inflammatory and non-inflammatory diarrhea.

The inflammatory diarrhea will be defined if 1) positive for C. difficile toxin or 2) stool WBC more than 5/HPF or 3) inflammatory mucosa or ulceration noted on colonoscopy.

The noninflammatory diarrhea will be defined if 1)negative for C. difficile toxin and 2) no WBC on stool examination and 3) dramatic response to diet adjustment or 4) no mucosal inflammation or ulceration if colonoscopy is performed

The patients who do not respond to diet modification, but do not undergo colonoscopy will be excluded because the definite diagnosis cannot be made.