To conduct the study the investigators will obtain detailed dietary, medical and lifestyle information on study subjects who undergo complete colonoscopy for diarrhea. The investigators will obtain colon biopsies from the right, transverse and left colon to evaluate adherent bacterial organisms. The investigators will draw blood to evaluate CYP2C19 polymorphisms and for future genetic studies. The prospective design corrects important limitations of prior research on MC. Successful completion of the study aims will improve the understanding of risk factors, set the stage for more scientifically grounded future research, and potentially suggest new interventions for a disease that is currently poorly understood.