Whipple disease is a rare condition that causes diarrhea, abdominal pain, difficulty in absorbing nutrients from food, weight loss, joint pain, swollen lymph nodes, and, in some cases, abnormalities of the nervous system. Whipple disease is thought to be caused by bacteria called Tropheryma whippelii (T. whippelii), which have been found in the tissue samples (particularly from the intestinal lining) of persons who have Whipple disease. Little is known about where these bacteria usually live or how people become infected with the bacteria and develop Whipple disease. Two recent studies reported that T. whippelii was found in persons without Whipple disease, but other studies have found no evidence of the bacteria in persons without the disease. These conflicting reports make it difficult for physicians to know what it means when T. whippelii is found in the tissues of patients.