Hot spring bath and Legionella pneumonia: an association confirmed by genomic identification.

A 59-year-old man developed pneumonia 9 days after bathing in a hot spring spa. Bilateral shadows on his chest radiograph rapidly progressed after admission. He was successfully treated with erythromycin and rifampicin. Legionella pneumophila serogroup 6 was recovered from an intratrachial specimen and a significant elevation was observed in a paired indirect fluorescent antibody to Legionella. Persistent slight fever and chest rentogenographic shadows resolved after administering low-dose prednisolone to treat organizing pneumonia shown by transbronchial lung biopsy. The same serotype of Legionella was recovered from the water of the hot spring spa where the man had bathed. When the extracted DNA of these two strains showed identical restriction fragments by pulsed-field gel electrophoresis, we had direct evidence that hot spring spas can be a source of Legionella pneumonia.