Don’t miss: Ischemic colitis, inflammatory causes.
Infectious
Non-inflammatory (non-bloody) causes (usually neg Fecal WBCs and neg FOBT)
-Viral gastroenteritis (most common cause): e.g.Rotavirus, Norovirus (Norwalk virus), adenoviruses, astrovirus, coronavirus
-Preformed toxins (food poisoning): Staphylococcus aureus, Bacillus cereus, Clostridium perfringens
-Produce toxins in GI tract: Enterotoxigenic E. coli, Vibrio cholerae
-Protozoa: Giardia lamblia, Cryptosporidium, Cyclospora, Isospora
Inflammatory/invasive causes (usually +Fecal WBCs and +FOBT)
-Campylobacter,
-Salmonella (non-Typhi species),
-Shigella,
-Shiga toxin–producing E. coli (e.g., E. coli O157:H7)
-Enteroinvasive E. coli,
-Clostridium difficile,
-Entamoeba histolytica,
-Yersinia
-Vibrio parahaemolyticus
Other infections
-Whipple’s disease
-STI (from unprotected anal sex): Neisseria gonorrhoeae, syphilis, lymphogranuloma venereum, herpes simplex
-Bacterial overgrowth (e.g., diabetes, blind loop after surgery)
-Listeria monocytogenes
-Human immunodeficiency virus
-Blastocystis hominis
Noninfectious
Irritable bowel syndrome
Drugs (antibiotics, caffeine, alcohol)
Malabsorption syndrome: Lactose intolerance, fructose intolerance
Celiac disease
Diabetes
Colitis: Microscopic colitis; Radiation colitis; Ischemic colitis;
Inflammatory bowel disease (Ulcerative colitis, Crohn’s disease)
Fecal impaction with leakage
Bypass operations
Reduced bile salts (e.g., postcholecystectomy)
Pancreatic insufficiency (pancreatitis, cystic fibrosis, cancer)
Scleroderma
Toxic shock syndrome
Laxative abuse
Cystic fibrosis
Emotional stress
Thinking through the differential diagnosis
Acute diarrhea means < 4 weeks of diarrhea.
Causes of diarrhea can be divided into infectious vs. non-infectious causes.
Acute infectious diarrhea is classified into two noninflammatory causes (mostly viral, milder disease) and inflammatory causes (mostly invasive or with toxin-producing bacteria, more severe disease).
*Avoid antibiotics if you suspect E. coli O157:H7 as it may increase the risk of HUS.
Further Reading
Am Fam Physician. 2014 Feb 1;89(3):180-189. Acute Diarrhea in Adults. https://www.aafp.org/afp/2014/0201/p180.html