What are the causes of bloody diarrhea?

Causes of Bloody Diarrhea

Bloody diarrhea most commonly results from infectious colitis (Campylobacter, Salmonella, Shigella, STEC, C. difficile), diverticulosis, angiodysplasia, ischemic colitis, and inflammatory bowel disease, with the specific etiology varying by patient age, clinical context, and associated symptoms. 1

Infectious Causes

Bacterial Pathogens

• Campylobacter, Salmonella, Shigella, and Shiga toxin-producing E. coli (STEC) are the most commonly identified bacterial causes of bloody diarrhea in North America, typically presenting with fever, abdominal pain, and inflammatory diarrhea 1
• Clostridium difficile causes pseudomembranous colitis and has doubled in incidence since 2001, with increasing community-acquired cases even without recent antibiotic exposure 1
• E. coli O157:H7 produces hemorrhagic colitis characterized by abdominal cramps, bloody diarrhea, and absent or low-grade fever, with histologic features resembling both ischemic and infectious injury patterns 2
• Yersinia enterocolitica should be considered when persistent abdominal pain and fever accompany bloody diarrhea, particularly with right-sided abdominal pain 1

Other Infectious Etiologies

• Enteric fever (typhoid/paratyphoid) should be suspected in febrile patients with travel history to endemic areas, though diarrhea is uncommon in these bacteremic illnesses 1
• Amoebic colitis causes bloody diarrhea with more indolent onset compared to bacterial dysentery, diagnosed by wet preparation showing amoebic trophozoites within 15-30 minutes of stool passage 1
• Cytomegalovirus (CMV) can cause bloody diarrhea in immunocompromised patients, diagnosed by demonstrating typical CMV inclusions on biopsy 1

Non-Infectious Structural Causes

Lower Gastrointestinal Bleeding Sources

• Diverticulosis accounts for 21-41% of acute lower GI bleeding cases across multiple studies, with prevalence increasing dramatically with age (>200-fold increase from age 20-80 years) 1
• Angiodysplasia represents 2-40% of lower GI bleeding cases depending on the study population, with higher prevalence in elderly patients 1
• Colorectal cancer and polyps account for 6-27% of acute lower GI bleeding presentations 1
• Hemorrhoids and anorectal lesions cause 5-24% of lower GI bleeding, though symptoms attributed to hemorrhoids frequently represent other pathology requiring proper evaluation 1

Ischemic and Radiation-Induced Disease

• Ischemic colitis is one of the most common causes of lower GI bleeding, typically presenting as acute abdominal illness with bloody diarrhea in elderly patients or those with cardiovascular risk factors 1, 3
• Endoscopic findings suggesting ischemia include normal rectum, sharply defined segments involving "watershed territory" (sigmoid to splenic flexure), petechial hemorrhages, and longitudinal ulcerations 1
• Radiation colitis occurs 9 months to 4 years after pelvic radiation therapy for prostatic or gynecologic malignancy, causing chronic bloody diarrhea 1

Inflammatory Bowel Disease

• Ulcerative colitis and Crohn's disease must be differentiated from infectious causes during acute presentations with bloody diarrhea 1, 4
• Diffuse, uniform mucosal abnormalities with rectal bleeding are hallmarks of ulcerative colitis, while perianal manifestations and skip lesions characterize Crohn's disease 4
• Flexible sigmoidoscopy with biopsy is essential in acute severe colitis to establish diagnosis and exclude infectious causes, with stool cultures positive in only 40-60% of infectious cases 1

Special Clinical Contexts

Immunocompromised Patients

• Empiric antibacterial treatment should be considered in immunocompromised patients with severe illness and bloody diarrhea before culture results return 1
• Neutropenic enterocolitis requires broad-spectrum antibiotics covering enteric gram-negatives, gram-positives, and anaerobes, with reasonable initial choices including piperacillin-tazobactam or imipenem-cilastatin 1

Upper GI Sources Mimicking Lower GI Bleeding

• Approximately 10-15% of patients presenting with acute severe hematochezia have an upper GI source identified on upper endoscopy, emphasizing the importance of excluding upper GI bleeding 1, 5
• Small bowel sources account for 0.7-9.0% of severe hematochezia cases 1, 5

Critical Diagnostic Pitfalls

• STEC O157 and other Shiga toxin 2-producing STEC infections must be considered in any patient with bloody diarrhea, particularly when fever is absent, as antimicrobial therapy should be avoided due to increased risk of hemolytic uremic syndrome 1
• Intestinal tuberculosis can mimic Crohn's disease but is distinguished by patulous ileocecal valve, transverse ulcers, and scar/pseudopolyp formation on colonoscopy 1
• Poor correlation exists between clinical and endoscopic severity indices during acute IBD flares, necessitating endoscopic evaluation for accurate assessment 1