Rapidly expanding lung abscess caused by Legionella pneumophila in immunocompromised patients: a report of two cases.

We describe two cases of lung abscess caused by Legionella pneumophila in immunocompromised patients. The first case had been treated initially with 60 mg prednisolone for ulcerative colitis, and L. pneumophila serogroup 1 was isolated from sputum samples after cavitation of the lung lesion. The second case was diagnosed as plasma cell lymphoma at post-mortem examination. L. pneumophila serogroup 5 was isolated from the contents of lung abscess, together with Enterococcus faecium and Prevotella intermedia in the post-mortem examination. Lung abscess caused by Legionella is unusual. Here, we discuss the difficulty of diagnosis of legionellosis in patients with unusual chest radiographic findings.