Clostridioides difficile

Quick Profile

• Classification: Gram-positive rod, spore-forming, obligate anaerobe
• Key labs: Toxin A and B PCR or EIA from stool; does not require culture
• Colonization: GI tract; spores survive on surfaces and resist alcohol hand sanitizers
• Clinical style: Antibiotic-disrupted flora → toxin-mediated colitis

Identification And Classification

• Organism family: Clostridiaceae
• Distinguishing feature: Large gram-positive rod producing heat-resistant spores
• Prior name: Clostridium difficile

Reservoir And Transmission

• Human GI tract and healthcare environment
• Fecal-oral route; spores are highly persistent on hospital surfaces
• Risk factors: Recent antibiotic use, hospitalization, proton pump inhibitor use, advanced age, immunosuppression
• Most common nosocomial infection in the United States

Virulence Factors And Pathogenesis

• Toxin A (enterotoxin): disrupts tight junctions, causing fluid secretion and mucosal damage
• Toxin B (cytotoxin): more potent; depolymerizes actin leading to cell death
• Both toxins work together to produce pseudomembrane formation
• Hypervirulent NAP1/BI/027 strain produces binary toxin and higher toxin levels

High-Yield Disease Patterns

Antibiotic-Associated Diarrhea

• Watery, non-bloody diarrhea after antibiotic exposure
• Most commonly after clindamycin, fluoroquinolones, and broad-spectrum penicillins and cephalosporins
• Onset can occur weeks after antibiotic course has finished

Pseudomembranous Colitis

• Severe form with profuse watery diarrhea, abdominal cramping, fever, and leukocytosis
• Colonoscopy shows yellow-white pseudomembranes overlying the colonic mucosa
• Hallmark clue: leukocytosis out of proportion to clinical appearance

Toxic Megacolon

• Life-threatening complication with colonic dilation greater than 6 cm
• Paradoxical decrease in diarrhea as motility fails
• Requires urgent surgical consultation

Diagnosis

• Preferred test: Stool PCR for toxin B gene (most sensitive)
• Stool EIA for toxins A and B (less sensitive but acceptable)
• Do not test asymptomatic patients or formed stool
• Colonoscopy if diagnosis uncertain or pseudomembranes needed for confirmation

Treatment And Resistance

First Episode, Non-Severe

• Oral vancomycin or oral fidaxomicin (preferred over metronidazole for initial episodes)

Severe Disease

• Oral vancomycin; add IV metronidazole if ileus is present preventing oral absorption

Recurrent Disease

• Second recurrence: fidaxomicin preferred
• Multiple recurrences: fecal microbiota transplant (FMT) is highly effective

Prevention

• Contact precautions with soap and water handwashing (alcohol does not kill spores)
• Antibiotic stewardship to reduce unnecessary broad-spectrum use

For antibiotic mechanisms and resistance, see Pharmacology: Antimicrobials.

Exam Traps

• Metronidazole is no longer first-line for initial C. diff episodes; vancomycin or fidaxomicin is preferred
• Alcohol-based hand sanitizers do not kill spores; soap and water is required
• Testing formed stool or asymptomatic colonization is misleading and should not be done
• A drop in diarrhea in severe C. diff may signal toxic megacolon, not improvement