Back
ditki Logo
medical & biological sciences

Gastroenteritis for the American Board of Internal Medicine (ABIM) Exam

Start your One-Week Free Trial
Already subscribed? Log in »
Gastroenteritis for the ABIM Exam
Definition
  • Gastroenteritis: Acute inflammation of the gastrointestinal tract, commonly caused by infectious agents, leading to symptoms of diarrhea, vomiting, abdominal pain, and fever.
    • Major causes: Viruses, bacteria, and parasites.
    • Non-infectious causes: Food allergies, toxins, and medications.
Etiology
  • Viral Gastroenteritis:
    • Rotavirus: Leading cause of severe diarrhea in children globally. Preventable via vaccination.
    • Norovirus: Most common cause of viral gastroenteritis in adults, particularly in closed settings (cruise ships, nursing homes).
    • Adenovirus and Astrovirus: Less common, typically affect children and immunocompromised patients.
  • Bacterial Gastroenteritis:
    • Escherichia coli (E. coli): Different strains cause different syndromes (e.g., Enterotoxigenic E. coli (ETEC) causes traveler’s diarrhea; Shiga-toxin producing E. coli (STEC) causes bloody diarrhea and hemolytic uremic syndrome).
    • Salmonella: Commonly linked to contaminated poultry, eggs, and dairy products. Can lead to enteric fever or severe bacteremia in immunocompromised patients.
    • Campylobacter: Associated with raw or undercooked poultry. Can lead to Guillain-Barré syndrome as a post-infectious complication.
    • Shigella: Highly contagious, often spread through contaminated food or water, causing dysentery.
    • Clostridioides difficile (C. diff): Associated with antibiotic use, leading to pseudomembranous colitis.
  • Parasitic Gastroenteritis:
    • Giardia lamblia: Acquired via contaminated water. Causes prolonged diarrhea with malabsorption.
    • Entamoeba histolytica: Causes amebic dysentery and liver abscesses, especially in areas with poor sanitation.
Pathophysiology
  • Inflammatory vs. Non-inflammatory Gastroenteritis:
    • Inflammatory: Typically caused by invasive organisms (e.g., Shigella, Campylobacter). Leads to bloody diarrhea (dysentery), fever, and leukocytosis.
    • Non-inflammatory: Typically caused by toxins or viral pathogens (e.g., Norovirus, ETEC). Leads to watery diarrhea without systemic signs.
  • Mechanisms of Diarrhea:
    • Osmotic diarrhea: Results from malabsorption (e.g., lactose intolerance, Giardia infection). Diarrhea improves with fasting.
    • Secretory diarrhea: Caused by toxins (e.g., cholera, ETEC) that stimulate intestinal secretion. Diarrhea persists during fasting.
    • Inflammatory diarrhea: Results from mucosal damage and invasion by pathogens, leading to bloody stools and tenesmus.
Clinical Features
  • General Symptoms:
    • Diarrhea: Can be watery or bloody, depending on the pathogen.
    • Vomiting: More common with viral etiologies.
    • Abdominal pain and cramping: Common in both viral and bacterial causes.
    • Fever: Typically seen in bacterial gastroenteritis.
    • Dehydration: The most severe complication, particularly in the elderly and infants. Signs include dry mucous membranes, tachycardia, hypotension, and decreased urine output.
  • Special Features:
    • Rotavirus: Severe dehydration in infants; presents with vomiting followed by watery diarrhea.
    • Norovirus: Explosive vomiting and watery diarrhea in adults, especially in outbreak settings.
    • STEC: Bloody diarrhea without fever; risk of hemolytic uremic syndrome (HUS) presenting with hemolysis, thrombocytopenia, and acute kidney injury.
Diagnosis
  • Clinical Evaluation:
    • History of travel, exposure to sick contacts, or consumption of high-risk foods.
    • Characterization of stool (e.g., watery vs. bloody) helps guide the diagnosis.
  • Laboratory Tests:
    • Stool Culture: Indicated in cases of severe diarrhea, bloody stools, or prolonged illness.
    • Stool for Ova and Parasites: Ordered when parasitic infection is suspected, especially in patients with prolonged symptoms or travel history to endemic areas.
    • C. difficile PCR: Essential in patients with recent antibiotic use or healthcare exposure presenting with diarrhea.
    • Fecal Leukocytes and Lactoferrin: Indicative of inflammatory diarrhea.
  • Other Diagnostics:
    • Rapid Antigen Tests: Available for pathogens like Rotavirus or Norovirus.
    • Polymerase Chain Reaction (PCR): Multiplex PCR can identify multiple pathogens simultaneously from stool samples.
Management
  • Rehydration Therapy:
    • Oral Rehydration Solution (ORS): The cornerstone of treatment, particularly for viral gastroenteritis.
    • Intravenous Fluids: Indicated for severe dehydration, inability to tolerate oral fluids, or shock.
  • Diet:
    • Clear fluids and gradual reintroduction of solid foods: Start with a bland diet once vomiting resolves.
    • Avoidance of lactose and caffeine: These may exacerbate symptoms during acute illness.
  • Pharmacological Treatment:
    • Antibiotics: Typically reserved for bacterial gastroenteritis. Indications include:
    • Shigella: Treat with fluoroquinolones or azithromycin.
    • Campylobacter: Macrolides (e.g., azithromycin) are first-line in severe cases.
    • C. difficile: Oral vancomycin or fidaxomicin.
    • Traveler’s Diarrhea: Azithromycin or fluoroquinolones for severe cases.
    • Antimotility Agents (e.g., Loperamide): Can be used in mild to moderate diarrhea but should be avoided in cases of bloody diarrhea or suspected C. difficile infection.
  • Probiotics:
    • May reduce the duration of illness in viral gastroenteritis and help prevent antibiotic-associated diarrhea.
Complications
  • Dehydration and Electrolyte Imbalance: Major concern, especially in vulnerable populations.
  • Hemolytic Uremic Syndrome (HUS): A serious complication of STEC infection, presenting with acute kidney injury, hemolysis, and thrombocytopenia.
  • Sepsis and Bacteremia: Can occur in patients with invasive bacterial infections (e.g., Salmonella) or immunocompromised individuals.
Prevention
  • Vaccination:
    • Rotavirus vaccine: Recommended in infancy to prevent severe diarrhea and dehydration.
    • Traveler’s vaccines: Hepatitis A and typhoid vaccines are recommended for individuals traveling to endemic regions.
  • Hygiene Measures:
    • Handwashing, especially after bathroom use and before eating.
    • Safe food handling practices, including proper cooking and storage of food.
    • Avoiding consumption of unsafe water, particularly in endemic areas.
  • Prophylactic Antibiotics: Occasionally recommended for high-risk travelers but generally not advised due to concerns about resistance.
Key Points
  • Gastroenteritis is commonly viral (Norovirus, Rotavirus), bacterial (Salmonella, E. coli), or parasitic (Giardia).
  • Key symptoms: Diarrhea (watery or bloody), vomiting, abdominal pain, fever, and dehydration.
  • Diagnosis: Primarily clinical, supported by stool studies in severe or prolonged cases.
  • Treatment focuses on rehydration (ORS or IV fluids). Antibiotics are reserved for specific bacterial infections.
  • Major complications include dehydration and, in some cases, HUS or sepsis.
  • Prevention includes vaccines (Rotavirus) and hygiene measures to reduce transmission.

Related Tutorials