Diarrhea – Claudio Tombazzi


  • >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
  • Inflammatory diarrhea: Salmonella, Campylobacter, Shigella, EHEC, Yersinia, E histolytica, invasive viruses (CMV, HSV), Non-cholera vibrio
  • SARS-CoV-2 has been shown to cause GI symptoms such as diarrhea and N/V
    • Medications (see below)
    • Any antibiotic can cause C. diff; the longer the treatment, the more likely
    • Most common to cause C. diff: Clindamycin >Penicillins/Ceph/Fluoroquinolones



  • Evaluate for red flags (BATS are Vulnerable vampires)
    • Bloody stools, Antibiotics/Recent hospitalization
    • Too many stools: >6 unformed stools/day, Sepsis (Fever)/Severe abdominal pain
    • Vulnerables (Age >70 yr, immunocompromised, IVDU, IBD, pregnant, travel



    • CBC w/ diff, BMP (eval for leukocytosis, AKI, electrolyte abnormalities)
    • C. diff  PCR
    • CRP/ESR (if inflammatory)
    • GIPP  (consider for patients with red flag symptoms (see above))
    • CT A/P if abdominal pain present
    • CT Enterography if concern for IBD
    • Blood Cultures (if febrile)



  • Systemic complications (dehydration, AKI, electrolyte abnormalities/acidosis)
    • PO intake (with solute i.e. Gatorade) or IVF if severe/unable to tolerate PO
    • Monitor and replace electrolytes
    • Downsides of abx: can precipitate HUS if 0157:H7, can prolong carrier state if salmonella, can precipitate C. diff
    • 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
  • Symptomatic therapy (Okay to use if C. diff ruled out)
    • Loperamide 4mg x1, 2mg after each loose stool (maximum 16mg/day) for 2 days
    • Lomotil 5mg every 6 hours until control achieved (can alternate with loperamide)
    • Probiotics may be helpful
  • C. diff positive (see section below)


Approach to Chronic Diarrhea


  • Secretory
    • Microscopic Colitis
    • Bile acid malabsorption
    • Carcinoid
    • Crohn’s disease (early ileocolitis)
    • Gastrinoma
    • VIPoma
    • Mastocytosis
    • Addison’s disease
    • Medication induced: antibiotics (i.e. Augmentin), caffeine, colchicine, NSAIDs, antineoplastics, antiarrhythmics (digoxin), metformin, carbamazepine
  • Motility
    • Hyperthyroidism
    • Diabetes 
    • Amyloidosis
    • Systemic Scleroderma
    • Medications: macrolides, metoclopramide, bisacodyl, senna, pyridostigmine
  • Osmotic
    • Lactose Intolerance
    • Bile salt diarrhea
    • Sugar alcohols: Sorbitol, mannitol, xylitol
    • Medications: citrates, lactulose, magnesium-containing antacids, mycophenolate, antibiotics (i.e. ampicillin, clindamycin), methyldopa, quinidine, propranolol, hydralazine, procainamide
  • Functional: IBS


Fatty (steatorrhea):​​​​​​​

  • Malabsorption
    • Celiac disease
    • Gastric bypass
    • Short bowel syndrome
    • Tropical Sprue
    • Whipple disease
    • Small intestinal bacterial overgrowth (SIBO)
    • Post-infectious malabsorptive diarrhea
    • Maldigestion
    • Pancreatic insufficiency
    • Hepatobiliary disorders



  • Diverticulitis
  • Ischemic colitis
  • Neoplasia
  • Radiation colitis
  • Arsenic poisoning
  • Microscopic colitis
  • Invasive infections: bacterial (tuberculosis, yersinosis), viral (CMV, HSV),
  • parasites (amebiasis, strongyloidiasis)
  • Inflammatory bowel disease (Crohn’s disease, Ulcerative Colitis)
    • Age of onset > 50
    • Rectal bleeding or melena
    • Nocturnal pain or diarrhea
    • Progressive abdominal pain
    • 1st degree relative with IBD or colorectal cancer Unexplained weight loss, fever, systemic symptoms



    • 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, >50 yo and hasn’t had one, or <50 yo and concern for IBD, CMV, ischemic colitis or microscopic colitis.
    • If concern for IBS: Rome IV criteria (abdominal pain 1d/week for 3 months with 2/3 of the follow: related to defecation, change in stool frequency, change in stool form)



    • 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)