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, which 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, travelers' diarrhea, antibiotic-associated diarrhea, sexually transmitted enteric infections, and Helicobacter pylori disease. Gastroenteritis in high-income countries (HICs), similar to upper respiratory infections, is common and an inconvenience, but it usually does not require a physician visit, laboratory evaluation, or antibiotic treatment. In a US surveillance network with a population-based telephone survey of 12 075 adults (1998–1999), about 0.72 episodes per person-year were documented. In the 2009 US National Ambulatory Medical Care Survey, diarrhea was the second leading gastrointestinal (GI) symptom prompting an outpatient clinic visit, an estimated 4.2 million in total. The Centers for Disease Control and Prevention (CDC) estimates that known foodborne pathogens account for an estimated 14 million illnesses, 60 000 hospitalizations, and 1800 deaths. In the United States in children, it is estimated that acute diarrhea causes 300 to 400 deaths annually. Globally, gastroenteritis is the second principal cause of mortality, after cardiovascular disease. It 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 5 to 20 in the low- and middle-income countries (LMICs).