## Epidemiological Characteristics of Shigella ### Correct Statements (Options 0, 1, 2) | Aspect | Details | |--------|----------| | **S. sonnei (developed countries)** | Most common in high-income nations; causes milder, self-limited disease; watery diarrhea without blood | | **Transmission route** | Fecal-oral via contaminated food/water; poor sanitation increases risk; endemic in developing regions | | **S. dysenteriae type 1** | Produces Shiga toxin; causes severe dysentery with bloody stools, high fever, and mortality up to 15% if untreated | ### Why Option 3 is Incorrect **High-Yield:** Shigella has an **extremely low infectious dose** — as few as **10–100 organisms** can cause infection. This is one of its distinguishing epidemiological features and explains why person-to-person transmission is actually **COMMON**, especially in closed environments (schools, daycare, military barracks). **Key Point:** The statement claims >10^6 CFU is required and that person-to-person transmission is rare — both are FALSE. Shigella is highly contagious precisely because of its low inoculum requirement. ### Epidemiological Patterns 1. **Developed countries:** S. sonnei predominant; sporadic cases; outbreaks in institutions 2. **Developing countries:** S. flexneri and S. dysenteriae type 1 common; endemic; high mortality in children 3. **Transmission:** Fecal-oral (primary); person-to-person (common); foodborne outbreaks (secondary) 4. **Infectious dose:** 10–100 organisms (extremely low) **Clinical Pearl:** The low infectious dose explains why Shigella spreads rapidly in daycare centers and why careful hand hygiene is critical for prevention. A single infected person can transmit to multiple contacts. **Mnemonic:** **SHIGELLA = SMALL Infectious Dose** — remember 10–100 organisms suffice, making person-to-person spread common. [cite:Harrison's Principles of Internal Medicine 21e Ch 155]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.