Differential Diagnoses for Acute Gastroenteritis

Infectious Etiologies

• The American College of Physicians and the Infectious Diseases Society of America recommend considering viral infections, such as norovirus, rotavirus, and adenovirus, as the primary differential diagnoses for acute gastroenteritis, with norovirus being the leading pathogen in adults and children following rotavirus vaccine introduction, presenting with vomiting, diarrhea, abdominal pain, myalgia, and low-grade fever after a 12-48 hour incubation period 1
• Norovirus is the most frequently detected pathogen (26% in adults with severe AGE), with symptoms typically resolving within 12-72 hours in immunocompetent hosts 2
• Rotavirus is 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, with incidence decreasing dramatically (up to 90%) in children due to vaccination 2
• Adenovirus and CMV primarily affect immunocompromised patients with impaired cellular immunity, causing prolonged courses with extended viral shedding 2, 3
• Nontyphoidal Salmonella accounts for 11% of AGE illnesses and 35% of hospitalizations, presenting with watery, mucoid, or bloody diarrhea, fever, and abdominal tenderness, and may cause bacteremia requiring combination therapy 1, 4
• Campylobacter represents 28% of bacterial pathogens in children <5 years, characterized by severe abdominal pain that may mimic appendicitis, and is associated with subsequent Guillain-Barré syndrome 1, 5
• Shigella causes dysentery syndrome with frequent, scant stools containing visible blood and mucus, fever, and severe abdominal cramping, accounting for 21% of bacterial pathogens in young children 1, 6
• Yersinia presents with severe abdominal pain mimicking appendicitis, and may be followed by reactive arthritis 5
• C. difficile should be suspected with recent antibiotic exposure, and can cause post-infectious IBS in up to 25% of cases, requiring specific testing and treatment 7

Non-Infectious Differentials

• Post-infectious IBS develops in approximately 9-10% of patients following acute gastroenteritis, and accounts for over 50% of all IBS cases, with risk factors including bacterial infection, female sex, younger age, psychological distress, and severity of initial illness 7
• Inflammatory Bowel Disease should be considered when symptoms exceed 14 days, particularly with persistent bloody diarrhea, weight loss >10%, or failure to respond to standard therapy, with fecal calprotectin testing helping to distinguish inflammatory from non-inflammatory causes 7

Clinical Approach to Differentiation

• The American Gastroenterological Association recommends laboratory investigation for patients with symptoms persisting beyond 7 days, visible blood in stool, fever with bloody diarrhea, severe abdominal cramping, or signs of systemic toxicity, recent antibiotic exposure, immunocompromised status, or suspected outbreak situation 1, 7
• Multiplex PCR testing is now preferred over traditional stool cultures, offering higher sensitivity (94% for norovirus) and faster results, with whole stool specimens detecting pathogens significantly more often than rectal swabs alone 2
• Blood cultures are indicated for suspected bacteremia, particularly with Salmonella or Yersinia, and fecal calprotectin helps distinguish inflammatory from non-inflammatory causes when IBD is suspected 4, 5, 7