A 28-year-old woman from rural Rajasthan presents with a 3-week history of watery diarrhoea, abdominal cramping, and low-grade fever. She reports consuming undercooked chicken at a wedding 4 days before symptom onset. Stool examination shows motile, curved gram-negative rods. Culture on selective media (Campy food agar at 42°C microaerophilic conditions) yields growth. What is the most likely causative organism and the recommended first-line antibiotic?

Explanation

## Diagnosis: Campylobacter jejuni Gastroenteritis ### Clinical Presentation Clues - **Incubation period:** 2–5 days (matches 4-day onset after chicken exposure) - **Presentation:** Watery diarrhoea with cramping and fever — classic for Campylobacter - **Risk factor:** Undercooked poultry is the most common source ### Microbiological Features **Key Point:** Campylobacter jejuni is a microaerophilic, curved gram-negative rod that grows optimally at 42°C (body temperature preference). **High-Yield:** Selective media (Campy food agar) with microaerophilic incubation (5% O₂, 10% CO₂, 85% N₂) at 42°C is the gold standard for isolation. Motility on wet mount is characteristic. ### Treatment **High-Yield:** First-line antibiotic is **Fluoroquinolone (Ciprofloxacin 500 mg BD for 5–7 days)** for moderate-to-severe disease or systemic symptoms. **Clinical Pearl:** In India, fluoroquinolone resistance is emerging in some regions, but it remains the first-line agent. Azithromycin (500 mg daily × 3 days) is an alternative, especially in children and pregnancy. ### Why Not Other Organisms? - **Salmonella typhi:** Enteric fever has a longer incubation (7–14 days), rose spots, and splenomegaly; blood culture is diagnostic. - **Vibrio cholerae:** Causes profuse "rice-water" diarrhoea without blood; epidemic context; different epidemiology. - **Shigella flexneri:** Dysentery (bloody diarrhoea) with tenesmus; different clinical picture. [cite:Park 26e Ch 18]