Hot spring bath as the reservoir of Legionella bacterium.

Legionella are widely distributed in natural and man-made environments. In these environments, legionella can utilize metabolic products excreted by blue-green algae and other general bacteria, on the other hand they can multiply intracellularly within amoebaebody. The major infection route of legionella is via 1-5 |Lim diameter aerosols which contain the legionella and reach humanalveolar septa. These aerosols are produced from cooling tower, evaporative condenser, shower, nebulizer, humidifier, whirlpool spa, hot spring spa, bubbling hot water bath, etc. In Japan, compared to Europe and USA, there have been manycases of legionellosis in relation to hot spring spa, and continuous circulating public and domestic hot water baths, not only by aerosolization but also by aspiration of water. There were a few cases of legionellosis in relation to hot springs in Europe and USA.But continuous water circulating public and domestic hot water bath system is specific in Japan. In Japan, hot spring bath water circulates and passes through a filterjust as the water of a continuous water circulating howwater bath. Amoebaecan attach to these filters and multiply by ingestion of bacteria. On these filters, legionella may become parasitic with amoebae. Comfirmative microbiological tests for legionellosis are recognized by detection of bacterial cells by direct fluorescent antibody testing in respiratory tract secretions and DNAdetection by PCRsystems in respiratory tract specimens as well as the isolation of legionella bacteria by culture. But to investigate the infection route or distribution rate of legionella, isolation of bacteria from the environment is necessary. Yabuuchi and colleages reported isolation of legionella from a hot spring bath in Japan (1). Subsequently, they reported isolation of legionella, amoebae, mycobacteria and Pseudomonas aeruginosa from domestic continuous water circulating bath water and sauna bath water (2-4). The most frequently distributing serogroupes of L. pneumophila in bath water were serogroup 4, 5 and 6 which differed from cooling tower water in which L pneumophila serogroup 1 had been most frequently isolated. Most of hot spring-related cases of legionella pneumonia were genetically confirmed with consistency of PFGE pattern between patients' strain and strains isolated from an epidemiologically-related source (5-7).