Diagnostic Considerations
Other conditions to consider in the differential diagnosis of gastroenteritis include the following:
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Various infectious etiologies
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Pseudomembranous colitis
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Food-borne toxigenic diarrhea
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Toxins
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Hormonal (vasoactive intestinal peptides)
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Drugs (ie, sorbitol, cholinergics, caffeine)
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Postsurgical complications
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Radiation colitis
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Carcinoid
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Pediatrics: adrenogenital/cystic fibrosis
Important considerations
It is important to recognize/diagnose the following conditions in patients:
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Dehydration or sepsis
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Immunocompromised patients and their potential, unusual etiologies or propensity to develop complications
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Hemolytic-uremic syndrome in patients with E coli infection
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Pseudomembranous colitis (C difficile)
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Toxic megacolon
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Appendicitis in patients who present with vomiting and diarrhea
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Noninfectious etiology, such as ischemic bowel, bowel obstruction, or other etiologies for abdominal symptomatology
Note the following:
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Avoid diagnosing gastroenteritis in a patient who is only vomiting when the vomiting is due to a nongastrointestinal and possibly life-threatening etiology
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Complications may result from the inappropriate use of antimotility and antiemetic medications.
Special concerns
Pseudomembranous colitis (C difficile)
Note the following:
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This condition occurs mostly in patients who are hospitalized or live in a nursing home and who have recently been on antibiotics and is due to infection with toxin-producing strains of C difficile. Toxins A and B damage the mucosa of the colon.
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Symptoms may range from mild to severe bloody diarrhea and colitis, with pseudomembranous colitis being the most severe form.
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Complications include dehydration, toxic megacolon, and perforation.
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Stop any antibiotics.
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Treat with intravenous fluids and vancomycin or metronidazole.
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Condition is suspect with prior or current antibiotic therapy.
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Diagnosis via assay or sigmoidoscopy.
Gastroenteritis in the elderly patient
Diagnosing complications, such as dehydration (may have chronic poor skin turgor and dry mucus membranes) is more difficult. Elderly patients may be unable to take needed medications. Electrolyte disorders and hypovolemia may have much more serious implications, and life-threatening abdominal emergencies, such as appendicitis, are easier to overlook. Fever may not be manifested, and pain sensation may be blunted.
Travelers' diarrhea
Note the following:
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The condition is usually self-limited (3-5 d).
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Onset is within 1 week of arrival.
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Fever, vomiting, and bloody stools are uncommon.
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Early treatment may decrease duration.
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Loperamide is often useful.
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If a lack of response to antibiotics is present, check for parasites.
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Consider C difficile in patients taking antibiotics.
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The use of probiotics, such as Lactobacillus GG, has had mixed results in treatment and prevention.
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Rifaximin at 200 mg PO tid may be used for the treatment or prevention of travelers' diarrhea. [32]
Food-borne toxigenic diarrhea
Note the following:
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The condition is usually self-limited and of short duration.
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Stool analysis and culture are not helpful.
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Perform supportive treatment only.
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Antibiotics rarely are useful or indicated.
Diarrhea in patients with acquired immunodeficiency syndrome (AIDS)
Note the following:
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The condition usually becomes more severe as the immune system deteriorates.
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Patient may require antimotility agents only.
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Consider drug-related and herb-related causes.
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Start with empiric treatment with a quinolone and culture the stool.
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Pursue diagnostic testing more aggressively because patients with AIDS are more likely to have an identifiable etiology.
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Consider nonopportunistic bacterial and protozoal infections first, followed by etiologies such as Cytomegalovirus (CMV) and Mycobacterium infections.
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Treatment must include nutritional and psychosocial support.
Differential Diagnoses
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Emergent Treatment of Gastroenteritis. Hektoen enteric agar with Escherichia coli colonies. Different growth media are necessary for identifying different enteric pathogens, suppressing the growth of nonpathogens, and allowing for chemical reactions to assist in identification. The appearance results from the organism's ability to ferment lactose placed in the medium. This results in the production of acid, which lowers the pH and causes a change in the pH indicator placed in the medium. Salmonella and Shigella organisms do not ferment lactose.
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Emergent Treatment of Gastroenteritis. Example of Salmonella on Hektoen enteric agar. The medium also contains ferric ammonium citrate, which indicates the production of hydrogen sulfide by the appearance of a black precipitate.
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Emergent Treatment of Gastroenteritis. The MacConkey medium is commonly used and differentiates lactose fermenters, which produce acid, decrease the pH, and cause the neutral red indicator to give the colonies a pink-to-red color.
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Emergent Treatment of Gastroenteritis. The Christensen method is used to determine if an organism produces the enzyme urease (Yersinia) or not (Salmonella, Shigella, Vibrio). Hydrolysis of urea produces ammonia and carbon dioxide, alkalinizing the medium and turning the phenol red from light orange to magenta (pink).
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Emergent Treatment of Gastroenteritis. Often, a combination of methods may be used for identification. The tube on the left is triple sugar iron (TSI) agar. The alkaline slant and acid butt (K/A) indicates an organism that ferments glucose only (not lactose or sucrose). The middle tube is indole positive, as indicated by the pink ring, and indicates the organism's ability to split tryptophan to form indole. The tube on the right is urease negative. Taken together, these tests indicate the organism is likely Shigella.
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Emergent Treatment of Gastroenteritis. Gram stain may be helpful in identifying an etiologic agent. This stain shows gram-negative bacilli, which could be Salmonella or Shigella with 2 polymorphonucleocyte cells (PMNs).
