What are the common diagnoses that cause diarrhea?

Common Diagnoses That Cause Diarrhea

Norovirus is the leading cause of acute diarrhea in the United States, accounting for 58% of all acute gastroenteritis cases, particularly in adults. 1

Viral Causes (Most Common Overall)

• Norovirus is the single most frequent pathogen causing diarrheal disease outbreaks and acute gastroenteritis across all age groups 1, 2
• Rotavirus remains the most common cause of acute diarrhea in children under 5 years, accounting for one-fourth of pediatric cases, though incidence has decreased significantly since vaccine introduction 1, 2
• Viral diarrhea characteristically presents as acute watery diarrhea without blood, often accompanied by vomiting, and is self-limited 1
• Other viral pathogens include sapovirus, astrovirus, and adenovirus, though these are less common 2

Bacterial Causes (Most Clinically Significant)

The most important bacterial pathogens causing diarrhea include:

• Salmonella species (12.1% of cases in surveillance studies) - causes the most hospitalizations and deaths in the United States 2, 3
• Campylobacter jejuni (4.9% of cases) - second most common bacterial cause 2
• Enterotoxigenic E. coli (ETEC) (8.0% of cases) - particularly common in traveler's diarrhea 2
• Shigella species - causes bacillary dysentery with fever, abdominal pain, and bloody diarrhea 4
• Shiga toxin-producing E. coli (STEC) - presents with severe abdominal pain and grossly bloody stools, but patients are typically NOT febrile (critical distinguishing feature) 4
• Yersinia enterocolitica - causes abdominal pain with high-grade fever 4

Key Clinical Distinction

Bacterial diarrhea presents with visible blood in stool, high fever, and pronounced systemic symptoms, whereas viral diarrhea is typically watery without blood. 1

Parasitic Causes

• Giardia lamblia and Cryptosporidium are the most common parasitic causes 1, 2
• Parasitic diarrhea characteristically persists for weeks to months with visible blood, mucus, and semiliquid consistency 1
• Entamoeba histolytica causes amoebic dysentery with bloody diarrhea and more indolent onset 5
• Approximately 10% of traveler's diarrhea is caused by parasitic infections, with giardiasis being most common 2

Special Pathogen: Clostridioides difficile

• C. difficile must be considered in any patient with recent antibiotic exposure within 8-12 weeks 4, 1
• Incidence of severe C. difficile infections has doubled since 2001 5
• Community-acquired cases are increasing, even with minimal or no antibiotic exposure 5

Context-Specific Causes

Traveler's Diarrhea

The majority is caused by bacterial pathogens, with ETEC being most common, followed by Campylobacter, Salmonella, and Shigella 5, 2

Immunocompromised Patients

Broader differential includes opportunistic pathogens such as CMV, Mycobacterium avium complex, microsporidia, Cystoisospora belli, and Cryptosporidium 2

Food/Water Exposure

• Vibrio species (including V. vulnificus) - consider with exposure to brackish water or raw/undercooked shellfish 4, 2
• Vibrio vulnificus particularly affects patients with chronic liver disease, iron overload, or hemochromatosis 2

Non-Infectious Causes to Consider

• Chronic pancreatitis - primary cause of steatorrhea with pale, bulky, malodorous stools 2
• Celiac disease - most common small bowel enteropathy in Western populations 2
• Bile acid malabsorption - diarrhea occurs after meals and responds to fasting, common after terminal ileum resection or cholecystectomy 2
• Medication effects - antiretroviral therapy, chemotherapy 2
• Endocrine disorders - hyperthyroidism, diabetes mellitus 2

Critical Clinical Pitfall

In up to 50% of patients with acute diarrhea, no pathogen is identified despite comprehensive testing. 5 This underscores that symptomatic treatment remains the cornerstone of management for most cases, with selective testing reserved for specific clinical scenarios (fever, bloody stools, severe symptoms, immunocompromised status, or persistent diarrhea >7 days) 1.