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.


METHODS
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.


METHODS
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.


METHODS
Risk factors for acquiring Legionnaires' disease.


RESULTS
There were 125 confirmed cases of Legionnaires' disease caused by Legionella pneumophila serogroup 1 associated with the Aquarium; 76% of patients were hospitalised, and four (3.2%) died. The Aquarium cooling towers were contaminated with this organism. Visiting the Aquarium was significantly associated with disease (odds ratio [OR], 207; 95% CI, 73-630). The case-control study indicated that current smoking was a dose-dependent risk (multivariable OR for currently smoking > 70 cigarettes/week, 13.5; 95% CI, 5-36), but chronic illness and duration of exposure at the site were not significant risks.


CONCLUSIONS
This study showed an association between poorly disinfected cooling towers at the Aquarium and Legionnaires' disease in visitors, and confirmed current smoking as a critical risk factor. The rapid response, publicity, and widespread urinary antigen testing may have resulted in detection of milder cases and contributed to the relatively low apparent morbidity and mortality rates. The urinary antigen test allows rapid identification of cases and may be changing the severity of illness recognised as Legionnaires' disease and altering who is considered at risk.
Greig
Jane E
JE
Communicable Diseases Section, Department of Human Services, Level 17, 120 Spencer Street, Melbourne, Victoria 3000, Australia.
Carnie
John A
JA
Tallis
Graham F
GF
Ryan
Norbert J
NJ
Tan
Agnes G
AG
Gordon
Ian R
IR
Zwolak
Bernard
B
Leydon
Jennie A
JA
Guest
Charles S
CS
Hart
William G
WG
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000389:Air Conditioning; D000942:Antigens, Bacterial / Q000652:urine; D016022:Case-Control Studies; D017714:Community-Acquired Infections / Q000453:epidemiology; D004196:Disease Outbreaks; D004780:Environment, Controlled; D005260:Female; D006801:Humans; D016952:Legionella pneumophila / Q000276:immunology / Q000302:isolation & purification; D007877:Legionnaires' Disease / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology; D014739:Victoria / Q000453:epidemiology; D014871:Water Microbiology
D000942:Antigens, Bacterial