enteritis (ĕnˌtərĪˈtĭs) [key], inflammation of the gastrointestinal tract. Acute enteritis is not usually serious except in infants and older people, in whom the accompanying diarrhea can cause dehydration through the loss of fluids. The condition known as regional enteritis or Crohn's disease is a chronic disease that occurs most frequently in young adults, producing a segmented thickening of the bowel wall and narrowing of the bowel opening (lumen). The lower portion of the small intestine is usually affected, but the infection can extend up to the esophagus and down into the colon. Clinical symptoms include mild, intermittent diarrhea, abdominal pain, weight loss, and fever. In prolonged cases there may be anemia and nutritional deficiency. The term enteritis is sometimes applied to the conditions of gastroenteritis (inflammation of the stomach commonly caused by food poisoning) and ulcerative colitis. Surgery may be necessary to treat severe complications such as abscesses and obstructions.