Vibrio Infection — RACP Adult Medicine MCQ

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HardInfectious DiseasesVibrio InfectionRACP Adult Medicine

A 40-year-old man develops severe watery diarrhoea, abdominal cramps, and dehydration while travelling in rural Northern Queensland during the wet season. Stool culture grows a Gram-negative curved rod that is oxidase-positive on TCBS agar. What is the most likely organism?

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Correct answer: A — Vibrio parahaemolyticus

Vibrio parahaemolyticus is associated with seafood consumption and warm coastal waters. However, in tropical northern Australia during the wet season, Vibrio cholerae serogroup O1 is the organism to consider if cholera-like illness is present. V. cholerae grows on TCBS (thiosulphate-citrate-bile salts-sucrose) agar and is oxidase-positive. However, given the location and severe presentation, the most likely organism among the options growing characteristically on TCBS is V. parahaemolyticus (seafood-associated) or V. cholerae. Treatment is aggressive rehydration; doxycycline shortens illness duration.

Reference: eTG – 2025 – Antibiotic Guidelines; CDNA – 2024 – Vibrio Guidelines