Important enteric parasites found in North America includeEntamoeba histolytica (amebiasis), Giardia lamblia, and Cryptosporidium parvum. Amebiasis occurs in warmer climates, whereas giardiasis is endemic throughout the United Statesand is common among infants in day care centers. E. histolytica infects the colon; amebae may pass through the bowel walland invade the liver, lung, and brain. Diarrhea is of acute onset,is bloody, and contains leukocytes. G. lamblia is transmitted through ingestion of cysts, either from contact with an infectedindividual or from food or freshwater or well water contaminated with infected feces. The organism adheres to the micro-villi of the duodenal and jejunal epithelium. Insidious onset ofprogressive anorexia, nausea, gaseousness, abdominal distention, watery diarrhea, secondary lactose intolerance, and weightloss is characteristic of giardiasis. Cryptosporidium causes mild, watery diarrhea in immunocompetent persons that resolveswithout treatment. It produces severe, prolonged diarrhea inpersons with acquired immunodeficiency syndrome (AIDS)(see Chapter 125).
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Gastroenteritis may be accompanied by systemic findings, suchas fever, lethargy, and abdominal pain. Patients often presentwith clinical syndromes. Viral diarrhea is characterized bywatery stools, with no blood or mucus. Vomiting may be present, and dehydration may be prominent, especially in infantsand younger children. Fever, when present, is low grade.
Typhoid fever is characterized by bacteremia and fever that usually precede the final enteric phase. Fever, headache, and abdominal pain worsen over 48 to 72 hours with nausea, decreased appetite, and constipation over the first week. If untreated, the disease persists for 2 to 3 weeks marked by significant weight loss and, occasionally, hematochezia or melena. Bowel perforation is a common complication in adults but is rare in children. Infected persons without symptoms, or chronic carriers, serve as reservoirs and sources of continuous spread.
Dysentery is enteritis involving the colon and rectum, with blood and mucus, possibly foul smelling stools, and fever. Shigella is the prototype cause of dysentery, which must be differentiated from infection with EIEC, EHEC, E. histolytica (amebic dysentery), C. jejuni, Y. enterocolitica, and nontyphoidal Salmonella. Gastrointestinal bleeding and blood loss may be significant.
Enterotoxigenic disease is caused by agents that produce enterotoxins, such as V. cholerae and ETEC. Fever is absent or low grade. Diarrhea usually involves the ileum with watery stools without blood or mucus and usually lasts 3 to 4 days with four to five loose stools per day.
A chief consideration in management of a child with diarrhea is to assess the degree of dehydration as evident from clinical signs and symptoms, ongoing losses, and daily requirements(see Chapter 33). The degree of dehydration dictates the urgencyof the situation and the volume of fluid needed for rehydration.Mild to moderate dehydration usually can be treated with oralrehydration; severe dehydration usually requires intravenous (IV) rehydration and may require ICU admission.
Initial laboratory evaluation of moderate to severe diarrhea includes electrolytes, blood urea nitrogen, creatinine, and urinalysis for specific gravity as an indicator of hydration. Stool specimens should be examined for mucus, blood, and leukocytes, which indicate colitis in response to bacteria that diffusely invade the colonic mucosa, such as Shigella, Salmonella,