Campylobacter jejuni

1. Campylobacter jejuni is classified under "inflammatory (large-bowel type)" gastroenteritis alongside Shigella, non-typhoidal Salmonella, EHEC, C. difficile, and Entamoeba histolytica — characterised by mucosal invasion, cytotoxin production, fecal PMN leukocytes, and mucoid ± bloody diarrhoea ^[2][3]. This classification table is extremely high-yield and has appeared repeatedly in GC lecture frameworks.

2. Campylobacter jejuni is the single most important infectious trigger of Guillain-Barré syndrome (GBS) via molecular mimicry between its lipo-oligosaccharide and human gangliosides (GM1, GD1a, GQ1b). The classic exam vignette: a patient with recent gastroenteritis developing progressive ascending symmetrical weakness with areflexia and albuminocytological dissociation in CSF ^[4].

3. Drug of choice for Campylobacter when antibiotics are indicated is erythromycin (macrolide), per HKUMed paediatric and microbiology teaching ^[5]. This contrasts with Salmonella typhi (3rd-gen cephalosporin or ciprofloxacin), Shigella (cotrimoxazole), and C. difficile (metronidazole → vancomycin) — examiners love asking "match the organism to the antibiotic."

4. C. fetus causes penetrating/systemic infection (enteric-fever-like) and appears in a different column from C. jejuni in the GE classification table ^[3]. This is a discriminator: if the vignette describes enteric fever features with Campylobacter, think C. fetus, not C. jejuni.

5. Antibiotics for Campylobacter GE are generally NOT recommended for uncomplicated cases — only of value if given early and in institutional settings to shorten bacterial excretion ^[5]. This mirrors the principle that most acute GE is self-limiting and antibiotics are not routinely indicated.

6. H. pylori was formerly classified as Campylobacter (called "Campylobacter pyloridis" historically) due to its spiral morphology — both are G−ve curved/spiral rods, but their clinical niches are completely different (stomach vs intestine) ^[1]. This is a favourite examiner trivia point.

• Inflammatory vs non-inflammatory diarrhoea: Campylobacter = inflammatory (fecal WBC +, bloody mucoid stool). If the vignette describes profuse watery diarrhoea with NO blood or WBC, think non-inflammatory causes (rotavirus, norovirus, ETEC, cholera).
• Campylobacter vs appendicitis: RIF pain with diarrhoea in a young patient after eating undercooked chicken → may mimic acute appendicitis. Key clue: preceding diarrhoea/fever + exposure history.
• GBS trigger: The commonest wrong answer is "Salmonella" or "Shigella" — but C. jejuni is THE organism most associated with GBS.
• Temperature for culture: 42 °C is a classic MCQ discriminator — most enteric organisms grow at 37 °C; Campylobacter requires the higher temperature.
• Fluoroquinolone resistance: In Hong Kong/Asia, fluoroquinolone resistance rates in Campylobacter are high ( > 50% in some series), making macrolides the preferred empirical choice.

No directly relevant past paper questions referencing Campylobacter jejuni by name were identified in the indexed past paper context provided (2016–2025 Fourth Summative MCQ, SAQ, and Minicase papers). The 2023 Minicase Case 2 (paediatric vomiting with intussusception) involves GI pathology in a child but centres on surgical management rather than Campylobacter specifically ^[6].

Note: Campylobacter is more likely to appear as a distractor or part of an EMQ/MCQ option list in GE or GBS questions. Students should be prepared for it in the context of:

• "Which organism is most associated with GBS?" → Campylobacter jejuni
• "Match the antibiotic to the GE organism" → Erythromycin for Campylobacter
• "Which organism causes inflammatory diarrhoea?" → Campylobacter among others