Gastroenteritis for Physician Assistant Licensing Exam

• Gastroenteritis: Inflammation of the gastrointestinal tract due to infectious agents, leading to diarrhea, vomiting, and abdominal discomfort.
• Common causes: Viruses, bacteria, and parasites.
• Non-infectious causes: Toxins, drugs, and food allergies.

• Viral Gastroenteritis:
• Norovirus: The leading cause in adults, transmitted via contaminated food, water, or direct contact.
• Frequently occurs in outbreaks (e.g., cruise ships, schools).
• Rotavirus: Major cause of severe diarrhea in infants and young children; vaccination has reduced its prevalence.
• Adenovirus and Astrovirus: Less common, usually affect children and immunocompromised individuals.

• Bacterial Gastroenteritis:
• Escherichia coli (E. coli):
• ETEC: Causes watery diarrhea, mainly in travelers.
• STEC: Produces Shiga toxin, leading to bloody diarrhea and hemolytic uremic syndrome (HUS).
• Shigella: Highly contagious, causes dysentery (bloody diarrhea).
• Salmonella: Transmitted via contaminated poultry, eggs, and dairy; causes gastroenteritis or enteric fever.
• Campylobacter jejuni: Associated with undercooked poultry; can lead to post-infectious complications such as Guillain-Barré syndrome.
• Clostridioides difficile (C. diff): Causes pseudomembranous colitis, typically after antibiotic use.

• Parasitic Gastroenteritis:
• Giardia lamblia: Acquired from contaminated water, causes prolonged diarrhea with malabsorption.
• Entamoeba histolytica: Causes amebic dysentery and can lead to liver abscesses.

• Viral Gastroenteritis:
• Causes damage to enterocytes, leading to impaired absorption of water and electrolytes.
• Rotavirus produces NSP4 toxin, leading to increased chloride secretion and watery diarrhea.

• Bacterial Gastroenteritis:
• Toxin-mediated: ETEC and Vibrio cholerae increase cAMP or cGMP, causing chloride secretion and watery diarrhea.
• Invasive bacteria: Shigella and Campylobacter invade the intestinal mucosa, leading to inflammation and bloody diarrhea.

• Parasitic Gastroenteritis:
• Giardia leads to villous atrophy and malabsorption, while Entamoeba histolytica invades the colonic wall, causing ulceration and dysentery.

• General Symptoms:
• Diarrhea: May be watery (viral or toxin-mediated bacterial causes) or bloody (invasive bacterial causes).
• Vomiting: More common in viral causes (e.g., Norovirus).
• Abdominal pain and cramping: Common in both viral and bacterial gastroenteritis.
• Fever: Typically present in bacterial gastroenteritis.
• Dehydration: Key concern, especially in children and the elderly.

• Specific Findings:
• Rotavirus: Watery diarrhea and vomiting in infants.
• STEC: Bloody diarrhea with risk of HUS (hemolytic anemia, thrombocytopenia, acute kidney injury).
• C. difficile: Severe watery diarrhea post-antibiotic use, pseudomembranous colitis in severe cases.

• Clinical Evaluation: Based on history of exposure, recent travel, food consumption, and symptom duration.
• Stool Culture: Recommended for bloody diarrhea or prolonged symptoms.
• PCR Testing: Rapidly identifies viral and bacterial pathogens.
• C. difficile Toxin Assay: Performed in cases of diarrhea after recent antibiotic use.
• Stool Ova and Parasites: Useful in prolonged diarrhea, especially after travel.

• Rehydration:
• Oral Rehydration Therapy (ORT): Preferred in most cases.
• Intravenous Fluids: Reserved for severe dehydration or shock.

• Pharmacological Treatment:
• Antibiotics: Reserved for bacterial infections (e.g., Shigella, C. difficile).
• Antimotility Agents: Can be used cautiously in non-bloody diarrhea; avoid in suspected C. difficile infection.

• Probiotics: May reduce the duration of diarrhea in viral gastroenteritis.

• Dehydration: Major concern, especially in infants, the elderly, and immunocompromised patients.
• Hemolytic Uremic Syndrome (HUS): Associated with STEC infection, presents with hemolysis, thrombocytopenia, and acute kidney injury.
• Guillain-Barré Syndrome: Rare neurological complication of Campylobacter infection.
• Toxic Megacolon: Seen in severe C. difficile infections.

• Vaccination: Routine rotavirus vaccination for infants.
• Hygiene: Handwashing, safe food handling, and clean water practices.
• Traveler’s Precautions: Avoiding high-risk foods and water in endemic regions; vaccines for cholera and typhoid in some cases.

• Common causes of gastroenteritis include viral agents (Norovirus, Rotavirus), bacteria (E. coli, Shigella, Salmonella), and parasites (Giardia, Entamoeba).
• Key symptoms: Diarrhea (watery or bloody), vomiting, abdominal pain, and dehydration.
• Rehydration is the mainstay of treatment; antibiotics are used selectively for bacterial infections.
• Diagnosis is clinical, with stool testing for severe or prolonged cases.
• Complications include dehydration, hemolytic uremic syndrome (STEC), and Guillain-Barré syndrome (Campylobacter).