Most Common Organisms Causing Colitis
Clostridioides difficile (C. difficile) is the most common identifiable infectious cause of colitis in hospitalized patients, accounting for 10-25% of all antibiotic-associated diarrhea cases and representing the dominant nosocomial pathogen. 1, 2, 3
Context-Dependent Etiology
The causative organism varies significantly based on clinical setting and patient characteristics:
Healthcare-Associated Colitis (Nosocomial)
- C. difficile is overwhelmingly the primary pathogen in hospital-acquired colitis, particularly after ≥3 days of hospitalization 4, 1
- After 3 days of hospitalization, standard enteric bacterial pathogens (Salmonella, Shigella, Campylobacter) become exceedingly rare, and routine stool cultures yield extremely low diagnostic value 1
- C. difficile is the main pathogen associated with nosocomial infections and the most common cause of diarrhea in hospitalized patients 4
Community-Acquired Infectious Colitis
When patients present with diarrhea at admission or develop colitis in the community, the most frequent invasive bacterial enteropathogens include 4, 5:
- Campylobacter jejuni
- Salmonella species (nontyphoid)
- Shigella species
- Shiga toxin-producing E. coli (STEC), particularly E. coli O157:H7
These four organisms represent the standard bacterial pathogens tested in stool cultures for community-acquired infectious colitis 4, 5
High-Risk Populations Requiring Broader Testing
Certain patient populations warrant expanded microbiologic evaluation beyond C. difficile 1:
- Immunocompromised patients (HIV-positive, transplant recipients, those on immunosuppressive therapy) may develop cytomegalovirus (CMV) colitis, which has high mortality if misdiagnosed 4
- Patients >65 years with significant comorbidities or neutropenia 1
- Recent international travelers or those from parasite-endemic regions may harbor Entamoeba histolytica or other parasitic causes 5, 6
Special Considerations for Immunocompromised Patients
- In transplanted patients, intestinal perforation due to diverticulitis is common following kidney and liver transplants 4
- CMV colitis should be suspected in patients with moderate to severe colitis, particularly those with corticosteroid-refractory disease 4
- Neutropenic enteritis (typhlitis) requires nonoperative management with broad-spectrum antibiotics unless perforation or ischemia develops 4
Critical Diagnostic Algorithm
For hospitalized patients developing diarrhea:
First-line testing: Single stool specimen for C. difficile toxin assay, especially if antibiotics received within 30 days 4, 1
If C. difficile negative AND no recent antibiotic use: Submit stool for culture targeting Campylobacter, Salmonella, Shigella, and E. coli O157:H7 4
Do NOT routinely culture after ≥3 days hospitalization unless patient was admitted with diarrhea, is HIV-positive, or part of outbreak investigation 1
Multiplex antimicrobial testing is now preferred over traditional stool cultures and microscopy 7
Common Pitfalls to Avoid
- Never use antimotility agents (loperamide, diphenoxylate) when C. difficile or any infectious colitis is suspected, as they can precipitate toxic megacolon 1, 2
- Recognize that absence of diarrhea does not exclude C. difficile—fulminant infection may present with ileus or toxic megacolon without diarrhea, particularly postoperatively 2, 3
- Alcohol-based hand sanitizers do not kill C. difficile spores; handwashing with soap and water is essential for infection control 4
- Environmental contamination with C. difficile spores can persist for months on surfaces, facilitating nosocomial transmission 4, 8
Risk Factors for C. difficile Colitis
The following increase risk 7-10 times 2:
- Antibiotic exposure (especially clindamycin, third-generation cephalosporins, fluoroquinolones, carbapenems)
- Advanced age >65 years
- Proton pump inhibitor use
- Hospitalization or long-term care facility residence
- Chemotherapy for cancer