Infectious Disease · Gastrointestinal Infections
The facts most likely to be tested
Clostridioides difficile is a Gram-positive, spore-forming, anaerobic bacillus that produces exotoxins A and B to cause mucosal injury.
Recent antibiotic exposure, particularly clindamycin, fluoroquinolones, or cephalosporins, is the most significant risk factor for developing infection.
The gold standard for diagnosis is the nucleic acid amplification test (NAAT) for the toxigenic C. difficile gene or a glutamate dehydrogenase (GDH) plus toxin enzyme immunoassay (EIA).
Oral fidaxomicin is the preferred first-line treatment for an initial episode of non-severe or severe C. difficile infection.
Oral vancomycin is an acceptable alternative first-line treatment if fidaxomicin is unavailable.
Fulminant C. difficile infection, characterized by hypotension, shock, ileus, or megacolon, requires high-dose oral vancomycin plus intravenous metronidazole.
Pseudomembranous colitis, visualized on colonoscopy as yellow-white plaques on the colonic mucosa, is the pathognomonic endoscopic finding.
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A 68-year-old male presents with 10 days of watery, non-bloody diarrhea and lower abdominal cramping. He was recently hospitalized for pneumonia and completed a 7-day course of levofloxacin. On physical exam, he has diffuse abdominal tenderness and a temperature of 100.8°F. Laboratory studies reveal a leukocytosis of 16,000/µL and a serum creatinine of 1.4 mg/dL (baseline 0.9 mg/dL).
What is the most appropriate first-line pharmacologic treatment for this patient?
Oral fidaxomicin
The patient presents with classic symptoms of C. difficile infection following fluoroquinolone use; per current guidelines, fidaxomicin is the preferred first-line agent for initial episodes.
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Etiology / Epidemiology
Associated with recent antibiotic use (clindamycin, fluoroquinolones, cephalosporins) and hospitalization.
Clinical Manifestations
Watery diarrhea, abdominal pain, and pseudomembranous colitis; leukocytosis is common.
Diagnosis
Stool NAAT for toxin gene is the gold standard; GDH plus toxin EIA is a common alternative.
Treatment
Fidaxomicin is the preferred first-line agent; avoid antimotility agents.
Prognosis
High recurrence rate of 20-30%; severe cases risk toxic megacolon.
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Epidemiology & Etiology
Primary risk factor is antibiotic exposure which disrupts normal colonic flora. Advanced age and proton pump inhibitor use are significant independent risk factors. Transmission occurs via the fecal-oral route, often in healthcare settings.
Pertinent Anatomy
The infection is localized to the colon. Severe inflammation can lead to thinning of the colonic wall, predisposing to perforation.
Pathophysiology
Ingestion of spores leads to colonization after flora disruption. Bacteria produce Toxin A (enterotoxin) and Toxin B (cytotoxin), which cause mucosal injury and inflammation. This results in the formation of pseudomembranes composed of fibrin, inflammatory cells, and necrotic debris.
Clinical Manifestations
Patients present with profuse, watery diarrhea, lower abdominal cramping, and low-grade fever. Physical exam may reveal tenderness; guarding or rebound tenderness suggests perforation. Pseudomembranous colitis is the hallmark endoscopic finding.
Diagnosis
The Stool NAAT (nucleic acid amplification test) is the most sensitive diagnostic tool. A GDH plus toxin EIA algorithm is frequently used to balance sensitivity and specificity. Do not test for cure as stool can remain positive after clinical resolution.
Treatment
Fidaxomicin is the first-line treatment for initial episodes. Oral Vancomycin is an acceptable alternative if fidaxomicin is unavailable. Avoid loperamide as it increases the risk of toxic megacolon. For fulminant cases, add IV Metronidazole.
Prognosis
Recurrence is common, occurring in 20-30% of patients. Monitor for toxic megacolon, characterized by colonic dilation >6 cm on imaging. Surgical consultation is required for patients with peritonitis or clinical deterioration.
Differential Diagnosis
Viral gastroenteritis: usually self-limiting and shorter duration
IBD flare: history of chronic bloody diarrhea and weight loss
Ischemic colitis: sudden onset pain out of proportion to exam
Enterotoxigenic E. coli: associated with recent travel
Microscopic colitis: chronic watery diarrhea with normal colonoscopy