Celiac disease affects 1% of the population. That is about 3 million people in this country. Out of those 3 million who have it, 97% of them are undiagnosed. For comparison, Alzheimers affects 2 million people in this country. Also, only 35% of celiac patients have the symptom of diarrhea. It is possible to have celiac disease and have no symptoms. Most physicians are taught that it is a disease so rare they will never see a patient with it. Therefore, many physicians will never even think to test for it. You can learn more facts about celiac disease by the links I've added under Learn About Celiac Disease.