Which of the following statements about Shigella is NOT correct?

Explanation

## Clarifying Shiga Toxin and HUS Risk in Shigella Infection ### Shiga Toxin: Presence vs. Clinical Manifestation **Key Point:** While Shigella dysenteriae type 1 (and rarely other species) produces **Shiga toxin (Stx)**, HUS is **NOT a universal or even common outcome** of Shigella infection. The statement that Shiga toxin "causes HUS in all infected individuals" is false and clinically misleading. ### Epidemiology of Shiga Toxin–Producing Shigella | Feature | Detail | |---------|--------| | **Shiga toxin producer** | Primarily *S. dysenteriae* type 1; rare in S. flexneri and S. sonnei | | **HUS incidence** | Occurs in <1% of Shigella infections overall; more common with S. dysenteriae type 1 | | **Risk factors for HUS** | Young age (<5 years), severe dysentery, delayed or ineffective antibiotic treatment | | **Mechanism** | Stx damages endothelial cells in kidneys and brain; thrombotic microangiopathy | **Warning:** Confusing "Shigella produces Shiga toxin" with "Shiga toxin causes HUS in all patients" is a common trap. Most Shigella infections resolve without HUS. ### Correct Statements About Shigella **Option 0 — TRUE:** *S. sonnei* (Group D) dominates in developed nations; *S. flexneri* (Group B) in developing countries. This epidemiologic pattern is well-established. **Option 2 — TRUE:** Shigella activates innate immunity through: - **NOD-like receptors (NLRs)** — detect cytoplasmic peptidoglycans - **Caspase-1 activation** — processes pro-IL-1β and pro-IL-18 - **IL-1β and IL-18 release** — drive inflammation and mucosal damage This is a key mechanism of Shigella-induced dysentery. **Option 3 — TRUE:** Antibiotic resistance in Shigella is rising globally: - **Plasmid-mediated** — ampicillin, trimethoprim-sulfamethoxazole (TMP-SMX) resistance - **Chromosomal mutations** — fluoroquinolone resistance (especially in Asia and Africa) - **Clinical impact** — limits empiric therapy options; surveillance data guide regional guidelines **High-Yield:** In many developing regions, fluoroquinolone-resistant Shigella is now endemic, necessitating culture and susceptibility testing for optimal management. ### Clinical Correlation **Clinical Pearl:** A child with bloody diarrhea and Shigella isolation should be monitored for HUS signs (oliguria, anemia, thrombocytopenia), but HUS is NOT an inevitable outcome. Most cases resolve with supportive care and antibiotics. [cite:Jawetz, Melnick & Adelberg's Medical Microbiology 28e Ch 16; Harrison's Principles of Internal Medicine 21e Ch 143]