[A case of Legionnaires' disease due to aspiration of hot spring water and isolation of Legionella pneumophila from hot spring water].

We report a case of fulminant pneumonia that was due to aspiration of contaminated hot spring water and was not affected by beta-lactam antibiotics. We suspected that the patient had Legionnaires' disease and treated the clinical symptoms with erythromycin. Legionellaceae could not be isolated from sputum or lung biopsy material, but an elevated titer to Legionella pneumophila serogroup 4 was found by indirect immunofluorescence test. We diagnosed the patent as having Legionnaires' disease with improved clinical symptoms. Furthermore, we went to the hot spring that he visited and tried to isolate Legionellaceae. Hot spring water was collected from the bathroom and water, hot water, and shower water from the guest-room. After using a low-pH method, samples were cultured on BCYE alpha medium. Serogroups are classified by agglutination method with immune rabbit serum. As a result, we successfully isolated Legionella pneumophila serogroup 4 from hot spring water (42 degrees C) from the bath. No bacteria could be isolated from the other samples. Therefore, we believe that this case of Legionnaires' disease was caused by aspiration of contaminated hot spring water. The infection route of Legionnaires' disease is unclear. There are no previous reports of isolation of Legionellaceae from Japanese hot springs. This case would provide important information when considering the infection route of Legionnaires' disease in Japan.