What is the diagnostic workup and treatment for infectious colitis?

Diagnostic Workup and Treatment for Infectious Colitis

Initial Diagnostic Approach

All patients with suspected infectious colitis require comprehensive stool testing for common bacterial pathogens, C. difficile toxin assay, and assessment of stool inflammatory markers, with endoscopic evaluation reserved for severe cases or when diagnosis remains uncertain. 1

Stool Studies (First-Line)

• Obtain stool specimens for bacterial culture including Salmonella, Shigella, Campylobacter, and Shiga toxin-producing E. coli (STEC) 2, 3
• Test all patients for C. difficile toxin using glutamate dehydrogenase antigen and toxin A/B enzyme immunoassays, or nucleic acid amplification tests 2, 1
• Multiplex PCR stool pathogen panels are preferred over traditional cultures as they provide faster results, though culture should follow positive PCR for antibiotic susceptibility testing 1, 4
• Measure fecal inflammatory markers (calprotectin or lactoferrin) to confirm colonic inflammation; fecal calprotectin >150 mg/g or elevated lactoferrin suggests active inflammation 5, 1
• Test for ova and parasites only if travel history suggests exposure, shellfish consumption, or residence in parasite-endemic regions 2, 1, 3

Laboratory Tests

• Complete blood count to assess for leukocytosis, anemia, and left shift 1, 6
• Comprehensive metabolic panel including electrolytes, creatinine, and liver function tests to evaluate for dehydration and electrolyte abnormalities 1, 6
• C-reactive protein (CRP) as an inflammatory marker, though it lacks specificity to differentiate infectious from other causes 1

Physical Examination Findings

• Vital signs assessment for fever, tachycardia, and hypotension indicating severe disease or septic shock 1
• Abdominal examination for tenderness, distension, and reduced bowel sounds 2, 1
• Digital rectal examination to assess for blood and perianal complications 2, 1

Imaging Studies

• CT abdomen/pelvis is indicated for patients with severe symptoms including high fever, significant abdominal pain, hemodynamic instability, or concern for complications like toxic megacolon or perforation 1
• Abdominal radiography in severe cases to exclude colonic dilatation, toxic megacolon, or perforation 1

Endoscopic Evaluation

• Flexible sigmoidoscopy with biopsies is preferred over full colonoscopy in moderate-to-severe disease due to lower perforation risk 1, 2
• Endoscopy is indicated when stool inflammatory markers are elevated, symptoms are severe, or diagnosis remains uncertain after initial workup 1
• Histology distinguishes infectious colitis from inflammatory bowel disease by preserved crypt architecture and acute inflammation (though very early disease may also show preserved architecture) 2

Severity Stratification

Severe infectious colitis is defined by: >6 bowel movements/day above baseline, fever, rigors, hemodynamic instability, peritoneal signs, WBC ≥15,000 cells/mL, creatinine elevation >50% above baseline, or elevated serum lactate 1

Treatment Approach

General Management

• Oral rehydration for mild-to-moderate disease; nasogastric or intravenous hydration for severe illness 7
• Antiemetic, antimotility, and antisecretory agents can be used for symptom control 7

Antimicrobial Therapy

Empiric antibiotic therapy with azithromycin 1000 mg single dose is recommended for adults with febrile dysenteric diarrhea when invasive bacterial pathogens (Shigella, Salmonella, Campylobacter) are suspected. 3

Specific Pathogen Treatment

• C. difficile colitis: Vancomycin 125 mg orally four times daily for 10 days 8
• Shigella, Salmonella, Campylobacter: Azithromycin 1000 mg single dose or fluoroquinolones (if susceptible) 3, 9
• STEC (E. coli O157:H7): Avoid antibiotics as they may increase risk of hemolytic uremic syndrome 3
• Parasitic infections: Pathogen-specific antimicrobial therapy 7

When to Use Antibiotics

• High-risk patients: Age >65 years, immunocompromised, severely ill, or septic 6
• Complicated disease: Severe symptoms, persistent fever, bloody stools, or evidence of systemic toxicity 9, 6
• Routine antibiotics are NOT recommended for mild, watery diarrhea in immunocompetent adults 6

Special Considerations

• Screen for hepatitis B, hepatitis C, HIV, and tuberculosis if immunosuppressive therapy may be needed 1
• Discontinue or adjust immunosuppressive medications during active infection 5
• Monitor renal function in patients >65 years receiving vancomycin for C. difficile, as nephrotoxicity risk is increased 8

Common Pitfalls and Caveats

• Do not perform routine PCR without culture follow-up, as high detection rates in healthy controls may identify non-pathogenic colonization 2
• Normal inflammatory markers do not exclude moderate-to-severe inflammation in patients with typical symptoms 5
• Biomarkers cannot differentiate between infectious colitis and inflammatory bowel disease flare; both require exclusion of infection 5
• Avoid antibiotics in suspected STEC until pathogen is confirmed, as treatment may precipitate hemolytic uremic syndrome 3
• C. difficile in IBD patients may not present with typical pseudomembranes, making diagnosis challenging 10
• Cytomegalovirus testing should be reserved for steroid-resistant or severe refractory disease, particularly in immunocompromised patients 2, 10