Positive serology to Legionella longbeachae in patients with adult respiratory distress syndrome

In an observational study we measured the Legionella longbeachae antibody titre rise in patients mechanically ventilated for more than eight days during a two-month period. The patients were divided into two groups on the basis of the presence or absence of the adult respiratory distress syndrome (ARDS). In nine patients with ARDS all showed an antibody rise consistent with recent infection with Legionella longbeachae with a rise in titre (six patients) or a high titre after eight to ten days of ventilation (three patients). Three patients without ARDS did not show a rise in titre. Culture of the environment, ventilator circuits, humidifiers and humidification water did not reveal an environmental source of Legionella longbeachae in the Intensive Care Unit. Legionella longbeachae may, be implicated as a pathogenic organism in ARDS, or as a secondary nosocomial infection. Alternatively the antibody titre rise may represent an epiphenomenon and may not be related to Legionella longbeachae infection.