Diarrhea
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
- Heat-labile toxin
- 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.
- Cholera toxin (enterotoxin): “rice-water” 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
- Opioid receptor agonist that increases intestinal transit time
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.