[Distribution of Legionella spp. in hot spring baths in Japan]

We investigated the inhabitation of Legionella spp. in hot spring water in various regions in Japan. The following results were obtained. 1) Of 710 hot spring water samples nationwide, Legionella spp. was isolated from 204 samples (28.7%), covering all 47 prefectures. By region, the isolation rate was the highest at 31.0% in the Chugoku district, while the isolation rates in Hokkaido, Kinki, and Kyushu were low, ranging from 25.0 to 26.2%. The rate in Tohoku, Kanto, Chubu, and Shikoku districts was 28.6-30.7%. Regarding the isolation rate by pH of hot spring water, the isolation rate was 4.9% at pH 3 or lower, but 34.8% at pH 3.1-7.5. When pH was 7.6 or higher, the isolation rate was 24.8%. 2) Most frequently, the number of bacteria detected was below 10(2) CFU/100ml (98 samples, 48.0%). The count was between 10(2) and 10(3) CFU/100ml in 71 samples (34.8%), and between 10(3) and 10(4) CFU/100ml in 29 samples (14.2%). In 6 samples (2.9%), the count was higher than 10(4) CFU/100 ml. 3) Among the isolates identified, L. pneumophila was the predominant species, and particularly, serogroups 1 and 5 were frequently isolated. The above findings clarified that although the number of the bacteria is low, Legionella spp. inhabits hot spring water throughout Japan.