GASTROENTERITIS: Gastroenteritis, broadly defined, refers to any inflammatory process of the stomach or intestinal mucosal surface. However, the term usually refers to acute infectious diarrhea, a diarrheal syndrome of less than 2 weeks' duration that may be accompanied by fever, nausea, vomiting, abdominal pain, dehydration, and weight loss. This chapter provides an overview of the infectious enteritides. Other chapters consider food poisoning, traveler's diarrhea, antibiotic-associated diarrhea, sexually transmitted enteric infections, and Helicobacter pyloridisease. In developed countries, gastroenteritis, similar to upper respiratory infections, is common and annoying, but it usually does not require a physician visit, laboratory evaluation, or antibiotic treatment. Globally, it is the second-leading cause of mortality, after cardiovascular disease. Gastroenteritis is the leading worldwide cause of childhood death and of years of productive life lost, with approximately 12 600 deaths per day. Annual per-person attack rates range from 1 to 5 in the United States and Europe and up to 5 to 20 in the developing world. There are approximately 100 million cases per year among adults in the United States, nearly 50% of which require subjects to limit their activities for more than 24 hours, whereas 8% require consultation with a physician and fewer than 0.3% result in hospitalization.