📊 Acute Diarrhea (<14 days)
• Most common: viral gastroenteritis (rotavirus, norovirus, adenovirus)
• Bacterial: Salmonella, Shigella, Campylobacter, E. coli O157:H7
• Shigella: high fever, seizures, bloody stools
• E. coli O157:H7: hemorrhagic colitis → HUS in 10%
🩺 Chronic Diarrhea (>2-4 weeks)
• Toddler's diarrhea: 1-5 years, normal growth, undigested food, no night stools
• Celiac disease: TTG IgA screening, villous atrophy on biopsy
• IBD: pain awakens from sleep, weight loss, bloody stools
• Post-infectious: secondary lactase deficiency
⚠️ Red Flags
• Bloody diarrhea + HUS (E. coli O157:H7, Shigella)
• Fever + bloody stools + seizures → Shigella
• C. difficile after antibiotics
• Growth failure ± chronic diarrhea → malabsorption
🩺 Stool Studies
• Fecal leukocytes/blood: bacterial infection, IBD
• Reducing substances + pH <5.5: carbohydrate malabsorption
• Stool fat (Sudan stain): steatorrhea (CF, celiac)
• Calprotectin: IBD screen
• C. difficile toxin: recent antibiotics
📌 Decision strategy: Acute diarrhea is usually viral and self-limited. Bloody diarrhea = bacterial, monitor for HUS. Chronic diarrhea with normal growth → toddler's diarrhea most likely. Growth failure → malabsorption workup.