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Charles Oertli


  • 3 BM/day OR abnormally loose stool

  • Acute (<2 weeks), persistent (2-4 weeks), or chronic (>4 weeks)
  • 95% of acute diarrhea is self-limited & no additional treatment needed
  • Most cases of acute diarrhea are due to infections
  • Non-infectious etiologies become more common with increasing duration
  • Voluminous watery diarrhea more likely disorder of small bowel
  • Small volume frequent diarrhea more likely disorder of colon
  • Nocturnal diarrhea suggests an inflammatory or secretory etiology

Acute Diarrhea


  • Watery diarrhea: viral gastroenteritis (norovirus, rotavirus, enteric adenovirus), C. diff, C. perfringens, S. Aureus, Bacillus cereus, enterotoxigenic E. coli, Cryptosporidium, Listeria, Cyclospora, vibrio cholerae, (Giardia is typically more chronic), Tropheryma whipplei, COVID
  • Inflammatory diarrhea: Salmonella, Campylobacter, Shigella, EHEC, Yersinia, E histolytica, invasive viruses (CMV, HSV), Non-cholera vibrio. Look for red flag symptoms (see below).
  • Medications, specifically antibiotics


  • Evaluate for red flags (BATS are Vulnerable vampires)
    • Bloody stools,
    • Antibiotics/Recent hospitalization
      • Any antibiotic can cause C. diff; the longer the treatment, the more likely
      • Most common to cause C. diff: Clindamycin >> Penicillins/Cephalosporins/Fluoroquinolones
    • Too many stools: >6 unformed stools/day
    • Sepsis (Fever) or Severe abdominal pain
    • Vulnerable (Age >70 yr, immunocompromised, IVDU, IBD, pregnant, travel)


  • All patients: CBC w/ diff and BMP to eval for leukocytosis (C.diff), AKI, electrolyte abnormalities, thrombocytopenia/anemia (HUS), eosinophilia (parasites)
  • If red flag symptoms or diarrhea > 7d: ESR/CRP, C.diff, GIPP
  • If immunocompromised: consider CMV, MAC, microsporidia
  • If abdominal pain: consider CT A/P with IV contrast
  • If concern for IBD or hx of IBD: CT Enterography with PO and IV contrast
  • Blood Cultures if febrile/septic


  • All patients: supportive care with PO or IVF, electrolyte repletion
  • If C.diff negative or treatment for C.diff started, ok for symptomatic treatment with Loperamide
    • Start with Loperamide 4mg x1 then transition to 2mg QID (AC+HS) (maximum 16mg/day)
    • If fever or inflammatory symptoms and C.diff not back, ok for Bismuth subsalicylate (Pepto-Bismol) 30mL or 2 tablets q30min x8
  • Indications for antibiotics:
    • GIPP negative for Shigella, 0157:H7 (can precipitate HUS) and salmonella (can prolong carrier state)
    • Empiric antibiotic therapy ONLY if toxic appearance or high concern for progressive illness/decompensation
    • Ciprofloxacin 500 mg BID or levofloxacin 500 mg daily x 3-5 days
    • Azithromycin 500 mg daily x 3 days
    • Ampicillin + gentamicin used for pregnant women to cover for Listeria
    • C. diff positive (see section below)

Approach to Chronic Diarrhea

Causes of Watery Diarrhea
Secretory Motility Osmotic

Microscopic colitis

Bile acid malabsorption


Crohn’s disease




Addison’s disease




Systemic scleroderma

Lactose intolerance

Bile salt diarrhea

Sugar alcohols: sorbitol, mannitol, xylitol

Meds: antibiotics, caffeine, colchicine, NSAIDs, antineoplastics, antiarrhythmics (digoxin), metformin, carbamazepine Meds: macrolides, metoclopramide, bisacodyl, senna, pyridostigmine Meds: citrates, lactulose, magnesium-containing antacids, mycophenolate, antibiotics, propranolol, hydralazine, procainamide
Functional: IBS
Causes of Fatty Diarrhea (Steatorrhea)
Malabsorption Inflammatory

Celiac disease

Gastric bypass

Short bowel syndrome

Tropical Sprue

Whipple disease

Small intestinal bacterial overgrowth (SIBO)

Post-infectious malabsorptive diarrhea


Pancreatic insufficiency

Hepatobiliary disorders


Ischemic colitis


Radiation colitis

Arsenic poisoning

Microscopic colitis

Invasive infections: bacterial (tuberculosis, yersinosis), viral (CMV, HSV),

Parasites (amebiasis, strongyloidiasis)

Inflammatory bowel disease


  • Labs: CBC w/ diff, CMP, ESR/CRP, TSH, celiac serologies if high suspicion (anti-TTG)
  • Spot fecal elastase Steatorrhea (greasy, malodorous stools that float)
  • Colonoscopy indicated if alarm symptoms are present ( >45 yrs and hasn’t had one, or \<45 yrs and concern for IBD, CMV, ischemic colitis or microscopic colitis)
  • If concern for IBS: Rome IV criteria (see section on “IBS” below)


  • IBS: trial elimination diet/low FODMAP, antidiarrheals
  • Pancreatic insufficiency: enzyme replacement (Creon), consult nutrition for assistance
  • Celiac: eliminate gluten, will need outpatient nutrition follow-up
  • Bile acid malabsorption: can try cholestyramine (can affect absorption of other meds)