A 32-year-old man from rural India presents with acute watery diarrhea, fever, and abdominal cramping for 3 days. Stool culture isolates a gram-negative, microaerophilic, S-shaped bacterium that is oxidase-positive and grows at 42°C. What is the drug of choice for this infection?

Explanation

## Campylobacter jejuni Infection: First-Line Treatment ### Organism Identification **Key Point:** The clinical and microbiological features (gram-negative, S-shaped, microaerophilic, oxidase-positive, growth at 42°C) are pathognomonic for *Campylobacter jejuni*, the most common bacterial cause of acute gastroenteritis worldwide. ### Drug of Choice: Azithromycin **High-Yield:** Azithromycin (a macrolide) is the preferred first-line agent for *Campylobacter* gastroenteritis, especially in acute symptomatic disease. **Mechanism:** Azithromycin inhibits bacterial protein synthesis (50S ribosomal subunit), achieves excellent intracellular and mucosal concentrations, and reduces duration of diarrhea and bacterial shedding when given early. ### Dosing & Duration - **Azithromycin:** 500 mg once daily for 3–5 days (or 1 g as a single dose in some regimens) - Reduces symptom duration by ~1 day if started within 4 days of illness onset ### Alternative Agents | Agent | Role | Notes | |-------|------|-------| | Ciprofloxacin | Second-line | Fluoroquinolone; effective but resistance increasing; avoid if severe dysentery | | Erythromycin | Alternative macrolide | Less preferred than azithromycin; more GI side effects | | Doxycycline | Severe/invasive disease | Reserved for systemic or bacteremic cases | **Clinical Pearl:** Most *Campylobacter* gastroenteritis is self-limited; antibiotics are reserved for symptomatic patients, immunocompromised hosts, or severe/invasive disease. Antimotility agents (loperamide) should be avoided due to risk of toxic megacolon. **Warning:** Fluoroquinolone resistance in *Campylobacter* is now widespread in many regions (>50% in some studies), making azithromycin the preferred empiric choice. However, macrolide resistance is also emerging and varies geographically. ### Supportive Care - Fluid and electrolyte replacement (oral rehydration therapy) - Symptomatic management - Isolation precautions to prevent transmission [cite:Harrison 21e Ch 159]