An outbreak of Legionnaires' disease at the Melbourne Aquarium, April 2000: investigation and case-control studies.

Objective: To investigate the source and risk factors associated with Australia's largest outbreak of Legionnaires' disease.

Design And Setting: Epidemiological and environmental investigation of cases of Legionnaires' disease associated with visits to the Melbourne Aquarium; two case-control studies to confirm the outbreak source and to investigate risk factors for infection, respectively.

Participants: Patients with confirmed Legionnaires' disease who visited the Melbourne Aquarium between 11 and 27 April 2000 were compared (i) with control participants from the community, and (ii) with control participants selected from other visitors to the Aquarium during this period.