[Legionella pneumonia in a patient with positive culture results of Legionella pneumophila serotype 1 from bronchoalveolar lavage fluid but negative urinary antigen test results].

A 39-year-old man presented to a local physician complaining of fever, headache without cough or sputum. Abnormal shadows were found on chest X-ray films. Pneumonia was diagnosed and he was referred to our hospital, where chest computed tomography showed bilateral, multifocal, and patchy ground-glass opacities. Neither the urinary antigen test for Streptococcus pneumoniae nor that for Legionella was positive. Because he had visited a public spa several days before developing the fever and headache, and because hypophosphatemia was identified, we then suspected Legionella pneumonia. Bronchoalveolar lavage fluid yielded positive culture of Legionella pneumophila serotype 1. The Legionella urinary antigen is known to detect Legionella pneumophila serotype 1 infection; however, sensitivity and specificity of the test are 60-95% and > 99%, but care should be taken when urinary antigen test results are negative in suspected cases of Legionella pneumophila serotype 1 pneumonia. In the present case, bronchoalveolar lavage fluid was a useful method for diagnosing Legionella pneumonia.