What is the treatment approach for a patient with infectious colitis?

Treatment of Infectious Colitis

The treatment of infectious colitis depends critically on identifying the causative pathogen, as empiric antibiotics are generally NOT recommended for most cases due to modest benefits and potential harms, with the major exception being Clostridioides difficile infection which requires prompt antibiotic therapy. 1

Initial Diagnostic Approach

Immediate Testing Required

• Stool studies must include culture, C. difficile testing (toxin assay or PCR), and evaluation for inflammatory markers (fecal lactoferrin or calprotectin) 1, 2
• Blood work should include CBC with differential, serum creatinine, electrolytes, albumin, and C-reactive protein 1, 2
• Imaging (CT abdomen/pelvis) is indicated when severe symptoms, abdominal pain, or complications like perforation or toxic megacolon are suspected 1

Clinical Features Suggesting Specific Pathogens

• Bloody diarrhea WITHOUT fever: Consider STEC (Shiga toxin-producing E. coli) - test specifically for E. coli O157:H7 and Shiga toxin 1, 3
• Bloody diarrhea WITH fever: Suspect Salmonella, Campylobacter, Shigella, or C. difficile 1
• Recent antibiotic use or healthcare exposure: C. difficile is the primary concern 1, 2

Treatment Algorithm by Pathogen

Clostridioides difficile Infection (CDI)

For initial CDI, oral vancomycin 125 mg four times daily for 10 days OR fidaxomicin 200 mg twice daily for 10 days is first-line therapy. 2, 4, 5

Disease Severity Classification

• Non-severe CDI: WBC ≤15,000 cells/mL, creatinine <1.5 mg/dL, stool frequency <4 times daily 1, 4

  • Treatment: Oral vancomycin 125 mg QID × 10 days OR fidaxomicin 200 mg BID × 10 days 1, 4, 5
  • Metronidazole 500 mg TID × 10 days is an alternative only when vancomycin/fidaxomicin unavailable 1, 6

• Severe CDI: WBC ≥15,000 cells/mL, creatinine >1.5 mg/dL, fever, hemodynamic instability, peritonitis, or ileus 1, 4

  • Treatment: Oral vancomycin 125-500 mg QID × 10 days 1, 6, 5
  • If ileus present: Add rectal vancomycin 500 mg in 100 mL normal saline every 4-12 hours PLUS consider IV metronidazole 500 mg TID 1, 6

Recurrent CDI

• First recurrence: Oral vancomycin 125 mg QID × 10 days OR fidaxomicin 1, 6
• Second or subsequent recurrences: Vancomycin with tapered/pulsed regimen (e.g., decreasing dose by 125 mg every 3 days, then pulse dosing 125 mg every 3 days for 3 weeks) 1, 6

Critical Management Points for CDI

• STOP the inciting antibiotic immediately if clinically feasible 1, 4
• AVOID antiperistaltic agents (loperamide) and opiates - they worsen outcomes 1, 6, 4
• Surgical consultation required for perforation, toxic megacolon, severe ileus not responding to antibiotics, or lactate >5.0 mmol/L 1

Invasive Bacterial Pathogens (Salmonella, Campylobacter, Shigella)

Empiric antibiotics are NOT routinely recommended for most cases of invasive bacterial colitis, as the benefit is modest (approximately 1 day symptom reduction) and risks include prolonged bacterial shedding and antibiotic resistance. 1

When to Consider Antibiotics

Antibiotics should be reserved for: 1

• Severe infections with high fever, severe abdominal pain, or systemic toxicity
• Immunocompromised patients
• Patients with prosthetic devices or valvular heart disease
• Elderly patients (>65 years) or those with significant comorbidities

Antibiotic Selection (When Indicated)

• Empiric therapy (before culture results): Azithromycin 1000 mg single dose OR 500 mg daily × 3 days 3
• Fluoroquinolones (ciprofloxacin 500 mg BID × 5-7 days) are alternatives but resistance is increasing 1
• Directed therapy based on culture and susceptibility testing is preferred when available 1

Pathogen-Specific Considerations

• Campylobacter: Macrolides (azithromycin) most effective if started early in illness; benefit minimal if started >3 days after symptom onset 1
• Salmonella: Antibiotics NOT recommended for uncomplicated gastroenteritis (may prolong carrier state); treat only severe cases or high-risk patients 1
• Shigella: Antibiotics reduce symptom duration and bacterial shedding; azithromycin preferred due to resistance patterns 1

STEC (Shiga Toxin-Producing E. coli)

Antibiotics are CONTRAINDICATED in STEC infections - DO NOT treat with fluoroquinolones, β-lactams, TMP-SMX, metronidazole, or macrolides due to evidence of harm (increased risk of hemolytic uremic syndrome). 1

• Supportive care only: aggressive hydration and electrolyte management 1
• Monitor for hemolytic uremic syndrome development (hemolysis, thrombocytopenia, acute kidney injury) 1

Supportive Care for All Infectious Colitis

Fluid and Electrolyte Management

• Aggressive IV fluid resuscitation for volume depletion from diarrhea 1
• Electrolyte replacement (potassium, magnesium) as needed 1
• Albumin supplementation for severe hypoalbuminemia (<2 g/dL) in critically ill patients 1

Monitoring and Follow-up

• Daily assessment of vital signs, stool frequency/character, and abdominal examination 1
• Serial labs every 24-48 hours if severe: CBC, electrolytes, creatinine, CRP 1, 2
• Reassessment at 3 days: If no improvement, reconsider diagnosis (especially test for C. difficile if not already done) 2

Nutritional Support

• Enteral or parenteral nutrition if malnourished or unable to maintain oral intake 1
• Avoid prolonged fasting unless ileus or impending surgery 1

Common Pitfalls to Avoid

• Do NOT give empiric antibiotics for bloody diarrhea without considering STEC - this can cause life-threatening hemolytic uremic syndrome 1
• Do NOT use metronidazole as first-line for CDI - vancomycin or fidaxomicin are superior 2, 4
• Do NOT continue the inciting antibiotic in CDI - this dramatically increases recurrence risk 1, 4
• Do NOT use antidiarrheal agents in acute infectious colitis - they can precipitate toxic megacolon 1, 6
• Do NOT delay surgical consultation in severe CDI - mortality increases significantly with delayed intervention 1