Celiac disease is an autoimmune disorder of the small intestine that occurs in genetically predisposed people of all ages from middle infancy onward. Symptoms include chronic diarrhoea, failure to thrive (in children), and fatigue, but these may be absent, and symptoms in other organ systems have been described.
Between 0.5 and 1.0 percent of people in the United States are sensitive to gluten due to Celiac disease. Celiac disease constitutes an abnormal immune reaction to partially digested gliadin. It probably occurs with comparable frequencies among all wheat-eating populations in the world. Certain allergies and neuropathies are also caused by gluten consumption and inhalation. In some instances what is known as cross contamination can occur without the person even being aware that they are ingesting gluten. Reported examples occur when people share silverware or other eating instruments. Wheat allergy and celiac disease are different disorders.
(source: http://en.wikipedia.org/wiki/Gluten)