Acute Diarrhea Diagnosis and Management

Clinical Classification and Etiologies

Norovirus is the leading cause of acute gastroenteritis in the United States, accounting for 58% of cases, particularly in adults 2
Rotavirus was historically the most common pathogen in children <5 years before vaccine introduction, now superseded by norovirus 2
Viral diarrhea typically presents as acute watery diarrhea without blood, often with vomiting, and is self-limited 1
Common bacterial pathogens include Salmonella, Campylobacter, Shigella, Shiga toxin-producing E. coli (STEC), and Yersinia 1, 2, 4
Bacterial diarrhea presents acutely with visible blood in stool, high fever, and pronounced systemic symptoms 5
Giardia lamblia and Cryptosporidium are the most common parasitic causes, often tested together as primary parasitology examination 3
Parasitic diarrhea is characterized by persistent or chronic presentation lasting weeks to months, with visible blood, mucus, and semiliquid consistency 5

Infants <3 months are at higher risk for bacterial diarrhea and bacteremia 5, 4
Immunocompromised patients require broad differential including opportunistic pathogens 8, 4
Elderly patients have the highest hospitalization and death rates 2
Patients with chronic liver disease, iron overload, or hemochromatosis are at risk for invasive Vibrio vulnificus 8

Selective testing based on clinical presentation is recommended, not routine for all cases 4
Indications for stool testing include fever with diarrhea, bloody or mucoid stools, severe abdominal cramping or tenderness, signs of sepsis, immunocompromised status, recent hospitalization, and persistent diarrhea >7 days 4, 2, 9
Optimal specimen collection includes a single diarrheal stool specimen or rectal swab for bacterial detection only 4
Testing strategy for inflammatory/bloody diarrhea includes testing for Salmonella, Shigella, Campylobacter, Yersinia, and STEC 4
For STEC, use methods detecting Shiga toxin (or genes) and distinguish O157:H7 from other serotypes 4

Immediate concerns include blood in stool with unintentional weight loss, nocturnal diarrhea, symptoms <3 months with progressive worsening, and suspected HUS (bloody diarrhea with anemia, thrombocytopenia, renal dysfunction) 9

Do not use empiric antibiotics in immunocompetent patients with bloody diarrhea while awaiting results (strong recommendation) 3, 5
Avoid antibiotics in STEC O157 and Shiga toxin 2-producing STEC due to increased HUS risk 5
Do not miss C. difficile testing in healthcare-associated diarrhea or recent antibiotic exposure 6, 7