Pediatric Escherichia Coli Infections Workup

Updated: Oct 07, 2015
  • Author: Archana Chatterjee, MD, PhD; Chief Editor: Russell W Steele, MD  more...
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Workup

Laboratory Studies

See the list below:

  • Culture stools in all patients with bloody diarrhea for pathogenic Escherichia coli, primarily the 0157:H7 serotype. If exposure is suspected (ie, as in the case of a known outbreak), assay even watery stools without blood for these pathogens. Enterohemorrhagic E coli (EHEC) isolation from stool may be impossible by the time hemolytic-uremic syndrome (HUS) has developed; thus, when EHEC is suspected, a stool culture should be obtained as early in the illness as possible (eg, within the first week).
  • Routine stool cultures generally screen for Salmonella, Shigella and Campylobacter species. Because E coli organisms are normal fecal flora, laboratories must be advised specifically to assay for pathogenic E coli when a sample is submitted. Most 0157:H7 isolates do not ferment sorbitol; therefore, cultivation of specimens on sorbitol MacConkey medium is a convenient method for detection. Confirmation requires identification of presumptive isolates with O and H antiserum.
  • Detection of Shiga-toxin–producing E coli in contaminated food or a patient's stool specimens may present a diagnostic challenge because of low copy numbers in the sample. Recently, more sensitive nucleic acid amplification methods, such as polymerase chain reaction (PCR) assays, have been developed for rapid identification of this organism directly from clinical specimens. Multiplex PCR assays for detection of all categories of diarrheagenic E coli are also available. [2, 23]
  • Rapid enzyme immunoassays (nonculture tests) for E coli 0157:H7 have been developed. [24] Such tests may be available at large university hospitals or through reference laboratories. Stool culture remains the diagnostic criterion standard.
  • Enterotoxigenic E coli (ETEC) diarrhea (traveler's diarrhea) is primarily diagnosed by clinical history, and treatment is empirically initiated. Laboratory assays involve detection of the associated enterotoxin, usually by enzyme immunoassay, and are not widely available. [25]
  • Fecal leukocyte presence varies but is more likely with enteroinvasive E coli (EIEC). Stool guaiac testing may reveal occult blood. Test the stools of infants and toddlers with profuse watery diarrhea for rotavirus antigen, especially during fall and winter.
  • Other laboratory findings associated with bacterial enteritis are nonspecific. Electrolyte changes may reflect fluid loss, and CBC counts generally reveal an elevated leukocyte count with left shift.
    • Accurate urinary tract infection (UTI) diagnosis requires an appropriately collected urine specimen. A clean-catch specimen is acceptable if the child is able to provide it. If not, urethral catheterization or suprapubic bladder aspiration is necessary.
    • Externally collected bag urine specimens are unsuitable for accurate diagnosis of pediatric UTI, and use of this collection technique is strongly discouraged.
  • Externally collected urine samples are likely to be contaminated with skin or rectal flora, rendering them unreliable and their cultures uninterpretable.
    • Urinalysis results help make the decision whether to begin antibiotic treatment.
    • Urinary nitrite and leukocyte esterase are specific but poorly sensitive assays for UTI.
    • Pyuria strongly suggests a UTI, but may be absent even when infection is present.
  • Perform a urine culture despite negative urinalysis results, particularly in infants and children younger than 3 years.
  • All neonates with suspected sepsis should have specimens of blood, urine, and cerebrospinal fluid sent for culture and Gram stain prior to initiating antimicrobial therapy.
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Imaging Studies

See the list below:

  • Abdominal radiography is not necessarily indicated. Consider flat and upright views when the differential diagnosis includes appendicitis or obstruction, including constipation. A CT scan of the abdomen with contrast is more sensitive than plain radiography for detection of E coli– induced colitis. [26]
  • An air-contrast enema is both diagnostic and therapeutic for patients with a suspected intussusception.
  • All children with a documented UTI should have imaging studies of the urinary tract to exclude an anatomic abnormality or vesicoureteral reflux. Renal ultrasonography and voiding cystourethrography are the currently recommended tests. Schedule both tests promptly. Girls older than 10 years with their first UTI may not require such extensive evaluation.
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