A 28-year-old man from rural India presents with acute diarrhea, abdominal cramps, and fever for 3 days following consumption of undercooked chicken. Stool culture reveals a gram-negative, microaerophilic, spiral-shaped bacterium that is oxidase-positive and grows at 42°C. What is the most common Campylobacter species responsible for this presentation?

## Most Common Campylobacter Species in Foodborne Illness **Key Point:** Campylobacter jejuni is the most common Campylobacter species causing acute gastroenteritis in humans worldwide, accounting for >90% of Campylobacter-associated diarrhea. ### Epidemiology and Clinical Features **High-Yield:** C. jejuni is the leading bacterial cause of acute diarrhea in developed countries and is increasingly recognized in India. Transmission occurs through contaminated poultry, unpasteurized milk, and water. ### Organism Characteristics | Feature | C. jejuni | C. coli | C. fetus | C. lari | |---------|----------|--------|---------|--------| | **Optimal Temperature** | 42°C | 42°C | 37°C | 42°C | | **Microaerophilic** | Yes | Yes | Yes | Yes | | **Oxidase** | Positive | Positive | Positive | Positive | | **Frequency in GI disease** | >90% | 5–10% | <1% | <1% | | **Typical source** | Poultry, water | Pigs, poultry | Systemic infection | Shellfish | ### Clinical Presentation of C. jejuni 1. **Incubation period:** 2–5 days (range 1–10 days) 2. **Symptoms:** Watery or bloody diarrhea, abdominal pain, fever, malaise 3. **Duration:** Usually self-limited (5–7 days) 4. **Complications:** Guillain-Barré syndrome (post-infectious), reactive arthritis, bacteremia (rare) **Clinical Pearl:** C. jejuni is a known trigger for Guillain-Barré syndrome; serotypes O:19 and O:41 carry the highest risk due to molecular mimicry with gangliosides. ### Diagnostic Features **Key Point:** Culture on selective media (Campy agar or CCDA) at 42°C in microaerophilic atmosphere (5% O₂, 10% CO₂, 85% N₂) is the gold standard. The organism is oxidase-positive, catalase-positive, and shows characteristic spiral/S-shaped morphology on Gram stain. ### Why C. jejuni is Most Common 1. **Reservoir:** Poultry are asymptomatic carriers; colonization rates in chickens exceed 50% 2. **Transmission:** Easy contamination of meat during processing; low infectious dose (~500 organisms) 3. **Survival:** Tolerates refrigeration and survives on food surfaces 4. **Prevalence:** Accounts for 5–14% of acute diarrhea cases in India and globally [cite:Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases Ch 214]