The radiologic manifestations of Legionella pneumonia.

A number of radiologic features on chest X-ray may aid in diagnosis and management of the patient with legionella infection. The infiltrates in legionnaires' disease frequently progress despite initiation of appropriate antibiotic therapy. Pleural effusion is common and occasionally seen even in the absence of lung field infiltrates. Pleural-based infiltrates associated with pleuritic pain may mimic pulmonary embolism. Circumscribed peripheral densities are commonly seen in immunosuppressed patients. Cavitation is also a prominent feature in this patient group and may develop during clinical improvement. Radiographic severity does not correlate with clinical outcome. Resolution of infiltrates may be slow, and the tendency for delayed clearing should be considered before initiating further invasive diagnostic investigation. Infections due to Tatlockia (Legionella) micdadei and Legionella bozemanii are more commonly reported in immunocompromised hosts; the radiographic manifestations are similar to those seen in Legionella pneumophila infection in the immunosuppressed.