Campylobacter jejuni is one of those “classic Step bugs” that shows up everywhere: vignette diarrhea questions, Guillain-Barré associations, and stool culture trivia. If you can picture the typical exposure (undercooked poultry), the typical symptoms (often bloody diarrhea + fever), and the big complication (ascending paralysis), you’ll snag a lot of easy points.
Quick ID: What Is Campylobacter jejuni?
Campylobacter jejuni is a gram-negative, curved/comma-shaped (or “seagull-wing”) rod that is a leading cause of bacterial gastroenteritis in the US.
High-yield microbiology features
- Gram stain: Gram-negative curved rods
- Motility: Motile (polar flagella)
- Oxygen: Microaerophilic (likes low O₂)
- Oxidase: Oxidase-positive
- Culture clue: Grows best at 42°C (bird GI tracts → poultry link)
- Reservoir: Poultry is the big one; also unpasteurized milk, contaminated water, pets/farm animals
First Aid cross-reference: Microbiology → Gram-negative bacteria → curved rods; GI infections; associations with Guillain-Barré syndrome and reactive arthritis.
Epidemiology & Transmission (How It Shows Up in Vignettes)
Typical exposures
- Undercooked chicken (most classic)
- Unpasteurized milk
- Contaminated water
- Animal exposure (especially farm/pets; less common Step trigger)
Incubation
- Often ~2–5 days after ingestion (can vary)
Vignette pattern: “College student had a cookout with undercooked chicken → fever + abdominal cramping → bloody diarrhea.”
Pathophysiology: Why It Causes Bloody Diarrhea
Campylobacter primarily causes an inflammatory/invasive enteritis, classically affecting the jejunum/ileum and colon.
Core mechanisms (Step-relevant)
- Invasion of intestinal mucosa → inflammation
- Cytokine-driven neutrophilic response → fecal leukocytes
- Mucosal damage → blood and mucus in stool
What you see clinically from this path
- Fever (inflammatory)
- Crampy abdominal pain (can mimic appendicitis)
- Bloody diarrhea (dysentery picture)
Contrast anchor: This is not the “watery, noninflammatory traveler’s diarrhea” vibe (e.g., ETEC). Think inflammatory diarrhea.
Clinical Presentation (How Patients Look)
Typical symptom sequence
- Prodrome: fever, malaise
- GI phase: abdominal cramping + diarrhea
- Stool: can become bloody as inflammation worsens
High-yield features
- Fever + bloody diarrhea
- Severe abdominal pain (may mimic acute abdomen)
- Dehydration possible
Key differentials on Step exams
| Bug | Key clues | Stool type |
|---|---|---|
| Campylobacter jejuni | Undercooked poultry, microaerophilic, curved rod, 42°C | Often bloody, inflammatory |
| Shigella | Daycare, very low infectious dose, seizures in kids | Bloody, inflammatory |
| Salmonella (non-typhoidal) | Reptiles/poultry/eggs, osteomyelitis in sickle cell | Inflammatory ± blood |
| EHEC | Undercooked beef, no fever, HUS | Bloody, classically no fever |
| C. difficile | Recent antibiotics, pseudomembranes | Watery → can be severe |
Complications & High-Yield Associations (Test Favorite)
1) Guillain-Barré syndrome (GBS)
- Classic association: Campylobacter jejuni infection → GBS weeks later
- Mechanism: Molecular mimicry (antibodies cross-react with peripheral nerve gangliosides)
- Presentation: Ascending symmetric weakness, areflexia; can progress to respiratory failure
Step tip: If a vignette says “diarrhea a few weeks ago” + ascending weakness → strongly consider Campylobacter → GBS.
2) Reactive arthritis
- Asymmetric oligoarthritis after GI infection
- Often in the “can’t see, can’t pee, can’t climb a tree” framework (reactive arthritis), though that classic triad is most emphasized with Chlamydia—GI triggers (including Campylobacter) are also tested.
3) Post-infectious IBS (less Step-y but real)
- Persistent GI symptoms after infection
Diagnosis (What the Question Writer Wants)
Most cases are clinical
In real life, mild cases often don’t need an organism-specific diagnosis.
When testing is done (and what’s high-yield)
- Stool culture: curved gram-negative rods; growth at 42°C in microaerophilic conditions
- Stool studies: fecal leukocytes or lactoferrin may be positive (inflammatory diarrhea)
- Many labs now use stool PCR panels for rapid identification
Exam framing: If they mention “microaerophilic, grows at 42°C, curved rod” → they’re basically naming Campylobacter.
Treatment (Step 1 + Step 2 Practical)
Supportive care is first-line for most
- Oral rehydration (or IV fluids if severe)
- Electrolyte management
When to use antibiotics (common Step 2 angle)
Treat if:
- Severe disease (high fever, significant bloody diarrhea, severe pain)
- Immunocompromised
- Pregnancy (case-dependent)
- High-risk patients or prolonged symptoms
Drug of choice (classic)
- Azithromycin (macrolide)
Alternatives: Fluoroquinolones are less favored in many settings due to resistance patterns (Step exams increasingly like macrolides as the “safe” answer).
What not to do
- Avoid antimotility agents (e.g., loperamide) in bloody/inflammatory diarrhea—can worsen disease/complications.
High-Yield Memory Anchors
“CAMP” mini-checklist
- Curved gram-negative rod (“seagull wings”)
- Azithromycin if severe
- Microaerophilic, motile; grows at 42°C
- Poultry exposure; Paralysis (GBS) afterward
First Aid–Style Rapid Review (Exam Snapshot)
| Category | Must-know facts |
|---|---|
| Morphology | Gram-negative curved rod, “comma/seagull” |
| Metabolism | Microaerophilic, oxidase-positive |
| Source | Undercooked poultry, unpasteurized milk, contaminated water |
| Disease | Inflammatory diarrhea: fever, cramps, bloody stools |
| Diagnosis clue | Growth at 42°C in microaerophilic conditions; stool PCR/culture |
| Treatment | Mostly supportive; azithromycin if severe/high-risk |
| Big associations | Guillain-Barré syndrome, reactive arthritis |
Common USMLE Pitfalls (Avoid These)
- Mixing up EHEC vs Campylobacter
- EHEC: often afebrile, undercooked beef, HUS risk
- Campylobacter: fever common, poultry, microaerophilic/42°C
- Forgetting GBS timing
- Neurologic symptoms usually occur days to weeks after the diarrhea resolves.
- Overtreating mild disease
- Many cases are self-limited; antibiotics reserved for severe/high-risk.