Two cases of Legionnaires' disease and 1 of Pontiac fever occurred among the crew of a merchant ship operating off the shores of Australia. PCR assays identified potential sources in the ship's cabins. Modification of maritime regulations for Legionnaires' disease prevention in commercial vessels is needed for nonpassenger merchant ships.
Keywords: Australia; Indian Ocean; Legionella pneumophila; Legionnaires’ disease; PCR; Pontiac fever; bacteria; biofilm; cruise; deployable microbiology; environmental control; fomite; health threat assessment; merchant ship; occupational risk; outbreak investigation; pneumonia; pneumothorax; reservoir; respiratory; vessel.