What are the primary differential diagnoses and management options for acute gastroenteritis?

Differential Diagnoses for Acute Gastroenteritis

The primary differential diagnoses for acute gastroenteritis include viral infections (norovirus, rotavirus, adenovirus), bacterial pathogens (Salmonella, Campylobacter, Shigella, Yersinia, C. difficile), parasitic infections (Giardia), and non-infectious conditions including post-infectious IBS, inflammatory bowel disease, and medication-related diarrhea. 1

Infectious Etiologies

Viral Causes (Most Common)

Viruses account for the majority of acute gastroenteritis cases, with norovirus being the leading pathogen in adults and children following rotavirus vaccine introduction. 1, 2

• Norovirus: The most frequently detected pathogen (26% in adults with severe AGE), presenting with vomiting, diarrhea, abdominal pain, myalgia, and low-grade fever after a 12-48 hour incubation period; symptoms typically resolve within 12-72 hours in immunocompetent hosts. 1, 2

• Rotavirus: Detected in 18% of adults with severe AGE, characterized by diarrhea, vomiting, and fever lasting 4-7 days after a 1-3 day incubation period; incidence has decreased dramatically (up to 90%) in children due to vaccination. 1, 3, 2

• Adenovirus and CMV: Primarily affect immunocompromised patients with impaired cellular immunity (chronic lymphatic malignancy, post-transplant, alemtuzumab therapy), causing prolonged courses with extended viral shedding. 1

Bacterial Causes

Bacterial pathogens are less common than viral causes but warrant specific consideration in certain clinical contexts. 1

• Nontyphoidal Salmonella: Accounts for 11% of AGE illnesses and 35% of hospitalizations; presents with watery, mucoid, or bloody diarrhea, fever, and abdominal tenderness; may cause bacteremia requiring combination therapy. 1

• Campylobacter: Represents 28% of bacterial pathogens in children <5 years; characterized by severe abdominal pain that may mimic appendicitis; associated with subsequent Guillain-Barré syndrome. 1

• Shigella: Causes dysentery syndrome with frequent, scant stools containing visible blood and mucus, fever, and severe abdominal cramping; accounts for 21% of bacterial pathogens in young children. 1, 4

• Yersinia: Presents with severe abdominal pain mimicking appendicitis; may be followed by reactive arthritis. 1

• C. difficile: Should be suspected with recent antibiotic exposure; can cause post-infectious IBS in up to 25% of cases; requires specific testing and treatment. 1, 3

Parasitic Causes

• Giardia: Consider in cases with prolonged symptoms, especially with travel history or exposure to contaminated water; requires specific stool testing for diagnosis. 1

Non-Infectious Differentials

Post-Infectious Complications

Post-infectious IBS develops in approximately 9-10% of patients following acute gastroenteritis and accounts for over 50% of all IBS cases. 1, 3

• Risk factors include bacterial (rather than viral) infection, female sex, younger age, psychological distress, and severity of initial illness. 1
• IBS-M (mixed bowel habit) is the most common subtype, followed by IBS-D (diarrhea-predominant). 1
• Symptoms persist beyond the typical 3-8 day resolution period for viral gastroenteritis. 5

Inflammatory Bowel Disease

• Consider when symptoms exceed 14 days, particularly with persistent bloody diarrhea, weight loss >10%, or failure to respond to standard therapy. 1
• Fecal calprotectin testing can help distinguish inflammatory from non-inflammatory causes. 1

Medication-Related Causes

• Recent antibiotic use increases risk for C. difficile infection. 3
• Multiple medications can cause diarrhea as an adverse effect. 6

Clinical Approach to Differentiation

When to Pursue Diagnostic Testing

Laboratory investigation is not warranted for mild, self-limited diarrhea but should be pursued based on specific clinical and epidemiologic features. 1

Indications for stool testing include: 1, 3

• Symptoms persisting beyond 7 days
• Visible blood in stool (dysentery syndrome)
• Fever with bloody diarrhea
• Severe abdominal cramping or signs of systemic toxicity
• Recent antibiotic exposure (test for C. difficile)
• Immunocompromised status
• Suspected outbreak situation
• Recent travel to endemic areas

Diagnostic Modalities

• Multiplex PCR testing is now preferred over traditional stool cultures, offering higher sensitivity (94% for norovirus) and faster results. 1, 3
• Whole stool specimens detect pathogens significantly more often than rectal swabs alone (49% vs. lower detection rates). 2
• Blood cultures are indicated for suspected bacteremia, particularly with Salmonella or Yersinia. 1
• Fecal calprotectin helps distinguish inflammatory from non-inflammatory causes when IBD is suspected. 1

Critical Pitfalls to Avoid

• Do not assume viral etiology without considering bacterial causes in patients with fever, bloody stools, or severe symptoms, as these require antimicrobial therapy. 4
• Do not overlook immunocompromised status, as these patients experience more severe disease, prolonged symptoms lasting weeks, and higher mortality (up to 25% with norovirus in transplant patients). 1, 5
• Do not test for enteric pathogens beyond 72 hours of hospitalization unless clinical deterioration occurs, as community-acquired pathogens like SSYC are unlikely nosocomial infections. 1
• Do not use antimotility agents (loperamide) in patients with bloody diarrhea, high fever, or suspected C. difficile, as this may worsen outcomes and precipitate toxic megacolon. 6
• Do not forget to consider enteric fever in travelers returning from endemic regions (particularly South/Southeast Asia) presenting with fever, as this requires specific antibiotic therapy with ceftriaxone or ciprofloxacin for 14 days. 7