The patient in the question developed symptoms from Clostridium difficile during a hospitalization that emerged subsequent to treatment with clindamycin. Presumably, the clindamycin destroyed helpful bacteria that were colonizing the gut allowing C. Diff to proliferate and cause symptoms. Nosocomial infection and a hospital acquired infection are the same thing (also called healthcare-associated infection). A superinfection is a complication of drug therapy in which colonization and infection follows from immunosuppression. A more classic example of superinfection is the emergence of a yeast infection after bacterial treatment. Lastly, this infection could be considered an opportunistic infection because it arises in a setting that would not normally occur, specifically the destruction of the normal intestinal microbiota. The more common example of an opportunistic infection would be those that occur in patients with Acquired Immune Deficiency Syndrome (AIDS) when T cells drop below a certain level.