2 studies have linked depression and C. diff (clostridium difficile) infection, particularly with older people. C diff is a common cause of diarrhea that can be fatal in severe cases. In the first study the average age was 68 and in the second the average age was 58. The second study noted an association of infection with the use of certain antidepressants – Remeron, Prozac and trazodone. From New York Times.