Clostridium difficile. C. diff. Toxic Megacolon. Pseudomembranous colitis. This is definitely not a rose by any other name. For those of you who feel you should know all you can about the enemy, stay tuned. Our guest is Dr. Clifford McDonald, a medical epidemiologist in the Epidemiology and Laboratory Branch, Division of Health Quality Promotion, CDC. He has investigated Clostridium difficile outbreaks and written extensively on the subject.