## Pathophysiology of Enteric Fever **Key Point:** Rose spots are a classic clinical sign of enteric fever but are NOT pathognomonic and appear in only 5–30% of patients, not >80%. ### Correct Statements (Options 0, 2, 3) | Feature | Details | |---------|----------| | **Peyer's patches invasion** | Salmonella typhi invades M cells overlying Peyer's patches in the terminal ileum; this is the primary site of bacterial entry and intracellular replication | | **Vi antigen (virulence)** | Capsular Vi antigen is a key virulence factor that masks lipopolysaccharide, inhibits complement deposition, and promotes survival within macrophages | | **Intestinal perforation** | Occurs in 1–3% of cases, typically in the third week when necrosis of Peyer's patches is most extensive; a surgical emergency | ### Why Option 1 Is Incorrect **High-Yield:** Rose spots (small, blanching, maculopapular rash on the trunk) are classically associated with enteric fever but are: - Present in only 5–30% of patients (NOT >80%) - NOT pathognomonic — can occur in other infections (e.g., leptospirosis, rickettsial infections) - More common in fair-skinned individuals and may be missed in dark skin **Clinical Pearl:** The absence of rose spots does NOT exclude enteric fever; their presence is helpful but neither sensitive nor specific. ### Mnemonic for Enteric Fever Stages **WEEK-BY-WEEK:** - **Week 1:** Bacteremia, fever rises in a step-ladder pattern, headache, malaise - **Week 2:** Sustained high fever ("rose spots" may appear), hepatosplenomegaly, "rose spots" - **Week 3:** Peak toxemia, rose spots fade, risk of perforation and complications - **Week 4:** Defervescence if untreated (mortality risk peaks) **Warning:** Do not assume rose spots are always present — they are a helpful sign when seen but their absence does not rule out enteric fever.
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