DDx

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• Ischemic colitis

Infectious: noninflammatory (nonbloody)

• Viruses: Norwalk virus, rotavirus, adenoviruses, astrovirus, coronavirus
• Preformed toxin (food poisoning): Staphylococcus aureus, Bacillus cereus, Clostridium perfringens
• Toxin production: enterotoxigenic E. coli, Vibrio cholerae, Vibrio parahaemolyticus
• Protozoa: Giardia lamblia, Cryptosporidium, Cyclospora, Isospora

Infectious: invasive or inflammatory

• Shigella, Salmonella, Campylobacter, enteroinvasive E. coli, E. coli O157:H7, Yersinia enterocolitica, Clostridium difficile (e.g., pseudomembranous colitis), Entamoeba histolytica, Neisseria gonorrhoeae, Listeria monocytogenes

Associated with unprotected anal intercourse

• Neisseria gonorrhoeae, syphilis, lymphogranuloma venereum, herpes simplex

Noninfectious

• Drug reaction, especially antibiotics
• Ulcerative colitis, Crohn’s disease (inflammatory)
• Ischemic colitis (inflammatory)
• Fecal impaction (stool may leak around impaction)
• Laxative abuse
• Radiation colitis (inflammatory)
• Emotional stress
• Malabsorption syndrome