cause colitis, particularly after the use of antibiotics Parasitic infestations rarely lead to diarrhea in developed countries Giardia lamblia and Cryptosporidium should be considered, particularly in outbreaks in daycare centers, and Entamoeba histolytica, among immigrants or travelers from tropical areas; cryptosporidiosis also commonly affects patients with HIV These topics are covered later in this chapter, in the sections on travel medicine and HIV, respectively Current diagnostic techniques are unable to identify an etiologic agent in most of the remaining episodes Viral hepatitis is covered in Chapter 91 Gastrointestinal Emergencies Bacterial infections of the liver and bacterial cholangitis, almost exclusively abscesses, are rare in otherwise healthy children; more commonly, they complicate either an anatomic malformation (e.g., biliary atresia) or affect neonates or immunocompromised hosts Because calculi in the bile ducts rarely occur before adolescence, cholecystitis occurs much less often in children than in adults Occasionally, episodes are seen in teenagers or children predisposed to stone formation, as in the chronic hemolytic anemias Less commonly, salmonellosis, leptospirosis, or KD produces acalculous cholecystitis These diseases are discussed elsewhere in this chapter In childhood, peritonitis almost invariably reflects an intra-abdominal catastrophe that requires surgical intervention However, the accumulation of ascitic fluid in children with diseases such as nephrosis and cirrhosis allows the development of a primary infection of the peritoneum Gastroenteritis—Viral The most common etiologies of acute gastroenteritis (AGE) in the United States are viral, most commonly noroviruses and rotavirus, which comprise almost 40% of viral AGE in the United States Rotavirus has been on a major decline since the introduction of routine vaccination Please also see Chapter 23 Diarrhea Adenovirus, sapovirus, astrovirus, parechovirus, and bocavirus comprise an additional 30% of cases in preschool-aged children Most causes of viral gastroenteritis are self-limited in healthy children; however, young children can shed viruses in feces for weeks to months after acute infection, contributing to secondary spread in the community The most common symptoms are diarrhea and/or vomiting, crampy abdominal pain, and fever Signs on examination may include pyrexia, tachycardia, and hyperactive bowel sounds Hematochezia and high fever in the older child may suggest a bacterial etiology, as would a history of international travel to a developing nation No laboratory studies are indicated in uncomplicated gastroenteritis in the previously healthy child with mild dehydration Fecal leukocytes or stool lactoferrin is more indicative of a bacterial pathogen Gastroenteritis—Bacterial Five bacterial pathogens commonly produce gastroenteritis: Salmonella, Shigella, Yersinia, Campylobacter, and pathogenic E coli (Campylobacter, typhoid fever, and pathogenic E coli are discussed in the travel medicine section of this chapter) Together, these organisms cause approximately 10% of the diarrheal illnesses seen in children coming to the ED In underdeveloped countries and occasionally in the United States, Vibrio species must also be considered C difficile causes toxin-associated colitis, particularly in patients who receive antibiotics The most common antibiotic associated with C difficile is amoxicillin Salmonella, Shigella, Yersinia, and Campylobacter not normally inhabit the alimentary tract Thus, recovery of one of these organisms suffices for the diagnosis of gastroenteritis E coli, however, is part of the normal bowel flora, only occasionally assuming a pathogenic role Serotyping is useful for detecting E coli O157:H7, which along with related strains is capable of inducing hemolytic uremic syndrome (HUS), but identification of other disease-producing strains is not readily available to the clinician Hemolytic Uremic Syndrome Shiga toxin-producing E coli (STEC) can cause HUS and colitis The most common serotype causing HUS in the United States is E coli O157:H7, but Shigella, Campylobacter, and pneumococcus have also been associated with HUS The pathogen is spread via fecal–oral transmission, and recent cases have been linked to contaminated fruits and vegetables, undercooked beef, and use of community pools While HUS is rare, the morbidity and mortality are substantial and the disease can be difficult to diagnose in the early stages Children present with bloody diarrhea, followed to 10 days later by hematuria, oliguria, and altered mental status Laboratory findings include elevated BUN and creatinine, thrombocytopenia, and anemia The CDC case definition specifies that anemia must be accompanied by microangiopathic changes (e.g., schistocytes, burr cells, or helmet cells on peripheral smear), and that renal involvement may consist of hematuria, proteinuria, and elevated creatinine (≥1 mg/dL in children