[Isolation of Legionella species from hot springs used for foot-soaking]

We aimed to investigate the presence of Legionella species in hot-spring baths for feet, which have been rapidly increasing in number in Japan in recent years.

The investigations were conducted between March 2009 and November 2011, and hot springs throughout the country were sampled. Legionella isolates were confirmed on the basis of the method described in the "Manual for the countermeasure to legionellosis, 3rd Edition." In this method, the samples were concentrated and smeared on GVPCalpha agar medium after acid treatment and cultured for 7 days at 36 degrees C. Gram-negative rods that required L-cysteine were determined to be Legionella species. After the first identification using Duopath Legionella (Merck Ltd. Japan), isolates were identified on the basis of agglutination reaction of an immune serum or genetic examination.

Legionella was isolated from 56 of the 196 samples (28.6%) and was confirmed to widely inhabit hot-spring baths from Hokkaido to Kyushu. The isolation rates were the highest (40.9%) in facilities installed around railway stations, including those on platforms. The average microbial density of Legionella species per 100 ml of hot spring water was 1.0 x 10(1) CFU, with a maximum value of 1.0 x 10(4) CFU, although the microbial density in most of the samples (34 samples; 60.7%) was less than 10(2) CFU. Legionella pneumophila was the dominant strain, and 16 strains (23.9%) of serogroup 1 were isolated. In addition, 7 strains (10.4%) of Legionella londiniensis and 4 strains (6.0%) of Legionella rubrilucens were isolated.

Legionella species inhabit approximately 30% of all hot springs for foot-soaking in the country. Although the number of viable organisms is small, the dominant presence of Legionella pneumophila, a major pathogen responsible for legionnaire's disease, raises the possibility of legionnaire's disease in users of these hot springs. Therefore, each institute should understand the present distribution of Legionella species in these hot springs and undertake appropriate sanitary measures.