Epidemiology

---

Etiology

Watery diarrhea

Viral

	Norovirus (Norwalk) virus	Rotaviruses	Adenovirus	Astrovirus
Genome/structure	Positive ss RNA, non-enveloped, Star of David	ds RNA (11 segments), non-enveloped, Wheel-like	ds DNA, non-enveloped, type 40/41, fibers (penton)	Positive ss RNA, non-enveloped
High risk	Group settings, e.g., cruise ships	Infants	Infants, older children, adults	Infants, elderly, immunocompromised
Seasonality	Occurs year round	November-April peak	Late fall and winter peak	Winter peak
Vaccine	No	Yes Prevalence in developed countries has decreased dramatically due to vaccination.	No	No

Bloody diarrhea

• Campylobacter jejuni
  • Poultry, unpasteurized milk (natural gut flora in birds)
  • Contact with infected persons or infected animals (e.g., pigs, dogs, cats)

Pathophysiology

---

Inflammatory

• EHEC
  • Shiga-like toxin: bloody diarrhea
  • Enhanced cytokine release (mainly renal epithelial cells) → HUS (no invasion of host cells)
• Shigella
  • Spread from cell to cell → invasion of M cells (MALT)
  • Shiga toxin
• Campylobacter
  • Type IV secretion system (T4SS)
  • Cytolethal-distending toxin
• Non-Typhi Samonella
  • Flagellar motility
  • Endotoxin
• Clostridioides difficile
  • Toxin A (enterotoxin)
  • Toxin B (cytotoxin)
• Yersinia Enterocolitica
• Amebic Dysentery
• Vibrio parahaemolyticus/vulnificus

Noninflammatory

• ETEC
  • Heat-labile toxin
    • Overactivates adenylate cyclase → ↑ cAMP → ↑ secretion of chloride and water efflux into the intestinal lumen → watery diarrhea
  • Heat-stable toxin
    • Activation of guanylate cyclase → ↑ cGMP → ↓ NaCl reabsorption → water efflux into the intestinal lumen → secretory diarrhea
• V. cholerae
  • Cholera toxin (enterotoxin): “rice-water” diarrhea
    • Same with heat-labile toxin
    • Permanently activates Gs protein → overactivation of adenylate cyclase → ↑ cAMP → ↑ secretion of chloride and water efflux into the intestinal lumen → watery diarrhea.
• Giardiasis
  • Impaired function and structure of intestinal tissue, resulting in malabsorption and diarrhea
• Gastroenteritis from preformed enterotoxin (S. aureus, B. cereus)
  • See Food poisoning
  • S. aureus: Enterotoxin B
    • Forms pores in enterocyte membranes → leakage of Na+ and water into the intestinal lumen
• C. perfringens
  • Exotoxins
  • Clostridium perfringens alpha toxin
    • Acts as a phospholipase → degrades cell membranes and tissue.
  • Enterotoxin (heat-labile)
    • Responsible for food poisoning.
• Cryptosporidiosis
• Norovirus
• Rotavirus

Clinical features

---

---

Diagnostics

---

Treatment

Antidiarrheal agents

• Bismuth subsalicylate
  • Converts to bismuth and salicylic acid in the GI tract
  • Has antisecretory, antimicrobial, and antiinflammatory effects
  • Can be used in bacterial diarrhea
• Loperamide
  • Opioid receptor agonist that increases intestinal transit time
    • Loperamide acts on intestinal μ-receptors and inhibits intestinal peristalsis and intestinal fluid secretion, and increases sphincter tone.
  • Best initial treatment for chemotherapy-induced diarrhea
  • Cautions
    • Should not be used for > 48 hours without reevaluation of the patient

Warning

Loperamide should be avoided in patients with suspected invasive diarrhea with inflammatory features, as it reduces intestinal motility, which consequently increases the risk of bacterial colonization and invasion.

---