Pseudomembranous colitis is a very severe form of antibiotic associated colitis or diarrhoea. It is usually the result of the toxin of Clostridium difficile.
Most cases are hospital-acquired. Infection is faeco-oral, for example, via the patient's or staff's hands from a contaminated commode or equipment - rectal thermometer, sigmoidoscope, etc. Sixty percent of cases occur in the elderly.