How do you diagnose and manage infectious colitis?

Diagnosis and Management of Infectious Colitis

Diagnostic Approach

Infectious colitis should be diagnosed through stool testing for pathogens (including C. difficile toxin), assessment of inflammatory markers, and endoscopic evaluation with biopsy when the diagnosis remains uncertain or when differentiating from inflammatory bowel disease is necessary. 1

Clinical Presentation

Infectious colitis presents with inflammatory-type diarrhea characterized by:

• Bloody, purulent, and mucoid stools 2
• Fever, tenesmus, and severe abdominal pain 2
• Sudden onset of symptoms may suggest infection over IBD 1

Initial Laboratory Testing

Obtain stool specimens to exclude common pathogens and specifically test for C. difficile toxin in all patients with suspected infectious colitis. 1

Key stool tests include:

• Standard bacterial stool culture or PCR for Shigella, Salmonella, Campylobacter, and other invasive bacterial pathogens 1, 3
• C. difficile toxin assay - mandatory in all cases, especially with recent antibiotic exposure, immunosuppression, or corticosteroid use 1, 4
• Shiga toxin testing when STEC is suspected (low-grade or absent fever with acute dysentery) 1, 3
• Specialized studies based on epidemiologic factors: parasitic testing for endemic regions or travel history, viral PCR when indicated 1

Inflammatory Markers

Supportive laboratory tests include:

• Complete blood count - may reveal leukocytosis, thrombocytosis, or leukemoid reaction (particularly with Shigella) 1, 5
• CRP and ESR - elevated in bacterial colitis but cannot differentiate infectious from inflammatory bowel disease 1, 5
• Fecal inflammatory markers (calprotectin, lactoferrin) - indicate colonic inflammation but lack specificity to distinguish infection from IBD 1, 4

Endoscopic Evaluation

Sigmoidoscopy or colonoscopy with biopsy of abnormal mucosa should be performed when the diagnosis remains uncertain or to differentiate infectious colitis from inflammatory bowel disease. 1

Endoscopic findings help distinguish:

• Infectious colitis typically shows preserved crypt architecture with acute inflammation on histology 1
• IBD demonstrates crypt architectural distortion, basal plasmacytosis, and chronic inflammatory changes 1
• Biopsy from both inflamed and uninflamed segments improves diagnostic accuracy 1

Diagnostic Pitfalls

Critical caveats to avoid:

• C. difficile testing has high false-negative rates even in severe disease; repeat testing may be necessary if clinical suspicion remains high 6
• Normal inflammatory markers do not exclude infectious colitis - clinical judgment supersedes laboratory values 4
• Fecal inflammatory markers cannot differentiate between infectious colitis and IBD flare 4
• Early IBD may mimic infection with preserved crypt architecture; repeat endoscopy after 4 weeks may be needed if diagnostic doubt persists 1

Management

Antimicrobial Therapy

Pathogen-specific antimicrobial therapy should be initiated for all forms of infectious colitis except STEC. 3

• Empiric treatment for febrile dysentery: Azithromycin 1000mg single dose for suspected Shigella, Salmonella, or Campylobacter 3
• C. difficile colitis: Metronidazole or vancomycin (note: treatment fails in up to 25% of fulminant cases) 6
• STEC infection: Avoid antibiotics - associated with increased HUS risk 1
• Parasitic infections: Pathogen-specific antimicrobial therapy 7

Supportive Care

• Oral rehydration for mild-moderate symptoms 7
• Nasogastric or intravenous hydration for severe illness 7
• Antiemetic, antimotility, or antisecretory agents for symptom control 7
• Monitor electrolytes and renal function in severe cases 5

Special Populations

High-risk patients requiring treatment include:

• Immunocompromised individuals (elderly, steroid users, immunosuppressive therapy, HIV-positive) 8
• Patients with complicated disease 2
• Those with severe symptoms or systemic involvement 7

Follow-up Considerations

• Reassess patients not responding to initial therapy - consider noninfectious conditions including IBD, lactose intolerance, or post-infectious IBS 1
• Symptoms lasting ≥14 days warrant consideration of IBD or post-infectious complications 1
• Approximately 9% develop post-infectious IBS after acute gastroenteritis 7
• Follow-up stool testing may be required by local health authorities before return to childcare or food handling 1