What is the treatment for infectious colitis?

Treatment of Infectious Colitis

The treatment of infectious colitis depends critically on identifying the causative pathogen, with Clostridioides difficile requiring oral vancomycin 125 mg four times daily for 10 days for severe disease or oral metronidazole 500 mg three times daily for 10 days for non-severe disease, while bacterial colitis from invasive pathogens (Shigella, Salmonella, Campylobacter) should be treated empirically with azithromycin 1000 mg as a single dose in adults with febrile dysentery. 1, 2

Initial Assessment and Pathogen Identification

The first critical step is determining disease severity and obtaining appropriate diagnostic studies:

• Assess for severe colitis signs: fever >38.5°C, hemodynamic instability, signs of peritonitis (decreased bowel sounds, abdominal tenderness, rebound tenderness, guarding), marked leukocytosis (>15 × 10⁹/L), elevated serum creatinine (>50% above baseline), or elevated serum lactate 3

• Obtain stool studies immediately: multiplex PCR testing is now preferred over traditional stool culture as first-line testing, followed by guided culture on PCR-positive pathogens for antibiotic susceptibility 4

• Test specifically for C. difficile: this is mandatory in any patient with recent antibiotic exposure or healthcare-associated diarrhea 5

• Consider rigid sigmoidoscopy with biopsy: particularly important in first presentations of severe colitis to exclude inflammatory bowel disease and assess for pseudomembranous colitis 6

Clostridioides difficile Infection (CDI)

This represents the most common and potentially life-threatening form of infectious colitis requiring specific management:

Disease Severity Stratification

• Non-severe CDI: stool frequency <4 times daily, no signs of severe colitis, WBC <15 × 10⁹/L 1
• Severe CDI: presence of any severe colitis signs listed above 3, 1

Treatment Algorithm

For initial episode or first recurrence 3, 1:

• Non-severe disease with oral therapy possible: metronidazole 500 mg three times daily orally for 10 days 3, 1, 7

• Severe disease with oral therapy possible: vancomycin 125 mg four times daily orally for 10 days 3, 1, 7

• If oral therapy impossible (ileus): metronidazole 500 mg three times daily intravenously PLUS intracolonic vancomycin 500 mg in 100 mL normal saline every 4-12 hours and/or vancomycin 500 mg four times daily by nasogastric tube 3

For second or subsequent recurrence: vancomycin 125 mg four times daily orally for at least 10 days OR fidaxomicin 200 mg twice daily for 10 days 1

Critical Management Principles

• Avoid antiperistaltic agents and opiates completely - these prevent toxin clearance and can precipitate toxic megacolon 3, 1

• Discontinue proton pump inhibitors if not medically necessary 1

• Stop the inciting antibiotic if CDI was clearly induced by antibiotic use 3

• Monitor for treatment response: expect decreased stool frequency or improved consistency after 3 days with no new signs of severe colitis 3

Surgical Indications

Colectomy should be performed urgently for 3, 1:

• Perforation of the colon
• Toxic megacolon (radiological colonic distension with severe systemic inflammatory response)
• Systemic inflammation with deteriorating clinical condition not responding to antibiotics
• Severe ileus
• Serum lactate >5.0 mmol/L (operate before this threshold is exceeded)

Bacterial Colitis (Non-C. difficile)

Empiric Treatment for Febrile Dysentery

When invasive bacterial pathogens (Shigella, Salmonella, Campylobacter) are suspected based on fever and bloody diarrhea:

• Adults: azithromycin 1000 mg as a single oral dose 2
• This covers the most common invasive bacterial enteropathogens while awaiting culture results 2

Pathogen-Specific Considerations

• Shiga toxin-producing E. coli (STEC): do NOT use antibiotics as they may precipitate hemolytic uremic syndrome; suspect when acute dysentery occurs with only low-grade or no fever 2

• Once specific pathogen identified: initiate pathogen-specific antimicrobial therapy based on susceptibility testing for all forms except STEC 2, 8

• High-risk patients and complicated disease: antibiotics are mandatory even though many bacterial colitis infections are self-limiting 8

Supportive Care Measures

Regardless of etiology, all patients require:

• Intravenous fluid and electrolyte replacement: correct and prevent dehydration, maintain hemoglobin >10 g/dL with transfusion if needed 3

• Subcutaneous heparin: reduce risk of thromboembolism in severe colitis 3

• Nutritional support: enteral or parenteral route if malnourished 3

• Daily monitoring in severe cases: vital signs four times daily, stool chart recording frequency and character, FBC/CRP/electrolytes every 24-48 hours 3, 9

• Plain abdominal radiography: if colonic dilatation detected at presentation (transverse colon >5.5 cm) or clinical deterioration occurs 3

Common Pitfalls to Avoid

• Do not delay treatment while awaiting stool culture results - start empiric therapy immediately in severe presentations 9, 6

• Do not use antimotility agents in suspected CDI - this is contraindicated and can worsen outcomes 1

• Do not give antibiotics for STEC - look for the characteristic presentation of dysentery with minimal fever 2

• Do not miss CMV colitis in immunocompromised patients - this carries extremely high mortality and requires specific antiviral therapy with ganciclovir 9

• Monitor for systemic absorption in CDI with inflammatory bowel disease - these patients may have significant vancomycin absorption and require serum level monitoring 7