A 2-year-old child from rural India presents with acute watery diarrhea for 3 days, fever, and abdominal cramps. On examination, the child has signs of moderate dehydration (sunken eyes, reduced skin turgor, lethargy). Stool is mucoid with blood streaks. Which investigation is most appropriate to identify the causative organism?

## Investigation of Choice for Bloody Diarrhea with Systemic Symptoms **Key Point:** Stool culture and sensitivity is the investigation of choice for acute bloody diarrhea (dysentery) to identify invasive bacterial pathogens and guide antibiotic therapy. ### Clinical Presentation Analysis The presence of: - Mucoid stool with blood streaks (dysentery pattern) - Fever and abdominal cramps - Systemic symptoms (lethargy) These features are classic for **invasive bacterial diarrhea** (Shigella, Campylobacter, Salmonella, enteroinvasive E. coli), not viral or parasitic causes. ### Why Stool Culture is Indicated | Feature | Implication | |---------|-------------| | Blood in stool | Suggests mucosal invasion → bacterial pathogen | | Fever + systemic toxicity | Indicates inflammatory/invasive process | | Acute onset (3 days) | Acute bacterial infection pattern | | Abdominal cramps | Consistent with colitis from invasive organisms | **High-Yield:** Stool culture is the gold standard for diagnosing bacterial dysentery. It identifies the organism and provides antibiotic sensitivity, allowing targeted therapy rather than empirical broad-spectrum antibiotics. ### Diagnostic Yield by Organism Type 1. **Shigella** — most common cause of dysentery in India; highly invasive; culture-positive in 70–80% of cases within first week 2. **Campylobacter jejuni** — second most common; requires selective media (CAMPY agar) 3. **Salmonella** — less common in acute dysentery; still requires culture 4. **EIEC** — requires culture and virulence testing **Clinical Pearl:** In dysentery, stool culture should be collected early (within first 3–5 days) for maximum yield. A rectal swab in transport medium is acceptable if stool specimen cannot be obtained immediately. ### Timing and Specimen Quality - Collect stool before antibiotics are started (if possible) - Transport to lab within 2 hours or use Cary-Blair transport medium - Results available in 48–72 hours [cite:Park 26e Ch 9]