A 5-year-old boy from a slum in Mumbai presents with persistent bloody diarrhea, fever, and severe abdominal pain for 4 days. His mother reports that his 2-year-old sister developed similar symptoms 1 week earlier. Stool culture yields a gram-negative bacillus that is non-motile, does not ferment lactose, and produces Shiga toxin. The child develops oliguria and thrombocytopenia on day 5 of illness. Which complication is this child at risk for, and what is the most appropriate management?

Explanation

## Shiga Toxin-Producing Shigella & HUS Pathogenesis **Key Point:** Shiga toxin (Stx) is an AB toxin that inhibits protein synthesis in endothelial cells, causing thrombotic microangiopathy — the hallmark of hemolytic uremic syndrome (HUS). **High-Yield:** Shigella dysenteriae serotype 1 is the most notorious Shiga toxin producer. The classic triad of HUS is: 1. Microangiopathic hemolytic anemia (MAHA) 2. Thrombocytopenia 3. Acute kidney injury (oliguria) ## Clinical Presentation in This Case | Finding | Significance | |---------|-------------| | **Oliguria** | Acute kidney injury from Shiga toxin-induced glomerular capillary injury | | **Thrombocytopenia** | Platelet consumption in microthrombi | | **Bloody diarrhea** | Mucosal invasion and toxin-mediated endothelial damage | | **Fever** | Systemic inflammatory response | | **Family cluster** | Fecal-oral transmission; high attack rate in crowded settings | ## Mechanism of HUS ```mermaid flowchart TD A[Shiga Toxin Production]:::outcome --> B[Binds to Gb3 on Endothelial Cells]:::action B --> C[Inhibits 60S Ribosomal Subunit]:::action C --> D[Endothelial Cell Apoptosis]:::urgent D --> E[Platelet Aggregation & Microthrombi]:::urgent E --> F[Microangiopathic Hemolytic Anemia]:::outcome E --> G[Thrombocytopenia]:::outcome E --> H[Acute Kidney Injury]:::outcome F --> I[HUS]:::outcome G --> I H --> I ``` ## Management of HUS **Mnemonic: CARE = Cautious fluids, Avoid antibiotics, Renal support, Electrolyte correction** 1. **Fluid Management:** Restrict fluids to insensible losses + urine output; avoid overload (risk of pulmonary edema in renal failure) 2. **Avoid Antimotility Agents:** Increase toxin absorption and risk of toxic megacolon 3. **Avoid Antibiotics:** Antibiotic-induced bacterial lysis releases more Shiga toxin, worsening HUS 4. **Transfusion:** RBC transfusion only if Hb <7 g/dL; platelet transfusion only if active bleeding or <10,000/μL 5. **Renal Support:** Dialysis if severe oliguria/hyperkalemia/fluid overload 6. **Supportive Care:** Electrolyte correction, nutritional support, monitoring for extrarenal manifestations (CNS, pancreatic) **Clinical Pearl:** ~90% of HUS cases resolve with supportive care alone. Mortality is <5% in developed countries but higher in resource-limited settings due to delayed diagnosis and management. **Warning:** Do NOT give antibiotics empirically — this worsens outcomes in Shiga toxin-producing organisms. [cite:Harrison 21e Ch 157; Park 26e Ch 32]