Legionnaires' disease outbreak in south western Sydney, 1992. Clinical aspects.

Objectives: To document the clinical, laboratory and radiological features of patients with Legionella pneumophila serogroup 1 pneumonia during an outbreak, and probe for any relationship between clinical or laboratory features and outcome.

Design And Setting: Prospective identification of patients with Legionnaires' disease in an outbreak from 15-26 April 1992 in the South Western Sydney Area Health Service, centred on the Fairfield area.

Patients: Twenty-six patients (22 men, four women) were confirmed to have the disease, based on the presence of clinical features of pneumonia, with L. pneumophila serogroup 1 isolated on culture, or evidence of seroconversion.

Results: Seventeen patients (65.4%) were culture-positive for L. pneumophila serogroup 1 and nine were diagnosed on serological criteria. A direct fluorescent antibody (DFA) test of sputum performed well as a rapid diagnostic method. Twenty-three patients (89%) presented with hyponatraemia, 14 (54%) with renal impairment and nine of 19 (47%) with elevated serum creatinine phosphokinase levels. Overall mortality was 23% (71% for patients requiring mechanical ventilation). Eleven of 119 patients (10.2%) who did not have Legionnaires' disease showed serological evidence of previous exposure.

Conclusions: The duration of symptoms and severity of biochemical abnormalities at presentation were not related to outcome. The sputum DFA test is useful for rapid diagnosis during outbreaks.