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

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.

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.

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.

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.

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.