Diagnosis

The approach to diagnosis and successful treatment involves obtaining a medical history carefully, and selective laboratory testing. Most hospital laboratories provide various cultures and immunoassays of stool for the presence of the enteric pathogens. Routine stool culture for bacterial pathogens now includes Campylobacter jejuni, Y. enterocolitica, and Aeromonas in addition to Salmonella and Shigella. Subculturing for E. coli serotypes or stool assays for Clostridium difficile toxin activity are available. Enzyme immunoassays also are available to test stool for the presence of rotavirus, enteric adenovirus, and astrovirus.

Most children have a nonspecific gastroenteritis and not dysentery. Clinicians must assess the likelihood of defining a treatable etiology and, as a consequence, the indication for performing a stool culture. The presence of fecal leukocytes or positive guaiac testing has been used as a screening tool to identify children at increased risk for invasive bacterial enteric infection, but fecal leukocytes have poor sensitivity and guaiac testing has poor specificity. 9 Therefore, it is best to combine these tests with the clinical findings to determine the need for stool cultures. If a child is febrile and has abrupt onset of diarrhea occurring more than four times per day or blood in the stool, the illness is more likely to have been caused by a bacterial pathogen and stool cultures are indicated. 10 The likelihood of identifying bacterial pathogens is increased if the patient's stool or accompanying exudate contains polymorphonuclear leukocytes. 11

Anaerobic stool cultures and assay of stool for Clostridium difficile toxin activity should be obtained for children who have been receiving antibiotics and develop bloody diarrhea. A history of hiking or camping should prompt examination for ova and parasites. In addition, a swab of mucus or bloody exudate from the stool should be placed in transport medium and sent to the laboratory for culture of Shigella species. Shigella is a fastidious pathogen and is more likely to be recovered from a swab than from a fresh stool specimen. In cases of persistent or recurrent diarrhea, especially with weight loss or day-care center exposure or in immunocompromised children, stool samples should be collected in fixative and examined for G. lamblia, Entamoeba histolytica, and Cryptosporidium. Depending on geographic location or travel history, serologic testing for confirming E. histolytica infection may be indicated.

Dehydration caused by diarrhea is usually isotonic, and measurement of serum electrolytes is not necessary. It is most important, however, to be aware of the physical findings of hypernatremic dehydration (hyperirritability, sunken eyeballs and fontanel, parched mucous membranes, and thickened, doughy skin) and the special requirements for rehydrating these infants following initial fluid resuscitation. In children receiving intravenous (IV) therapy, electrolytes may be measured initially and during therapy.

Protracted vomiting and/or diarrhea occurring in infants and toddlers, in combination with fasting, may increase the risk of hypoglycemia. Measurement of blood glucose may be helpful in managing these patients.

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