Japanese Journal of Water Treatment Biology

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Many outbreaks of Legionnaires’ disease have been reported from cooling tower water overseas, but in Japan, bath water is the most common source of Legionnaires’ disease infection. Although the Ministry of Health, Labour and Welfare has issued a series of notices to promote the improvement of hygiene management standards, outbreaks of Legionnaires’ disease caused by hot spring facilities are still occurring.

The Tokyo Metropolitan Government’s regulations regarding sanitation of public bath that Legionella bacteria must be “not detected” in water. In the Tokyo’s regulations, the term “not detected” actually means that the concentration of Legionella bacteria must be less than 10 CFU/100 mL . If Legionella bacteria exceed 10 CFU/100 mL in bath water, the Tokyo Metropolitan Government （TMG） recommends improving sanitation of the facilities.

This present paper introduces the Legionella testing methods conducted by the TMG and reports on survey of Legionella bacteria in 2,072 bath water samples from facilities in Tokyo that were inspected by the government from FY2018 to FY2020.

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A cyanobacterium Raphidiopsis raciborskii （Wołoszyńska） Aguilera et al., which has not been reported from Lake Biwa, formed a bloom after October 2022 at a pond near the South Basin of Lake Biwa. The identification was confirmed by referring to the sequence of the rbcL gene by BLAST. The density of this species in the surface water reached 7.5×10³ trichomes/mL on November 3, 2022. This species has been considered tropical and forms blooms only above 25℃. At this pond, however, it continued to be dominant by December 20 when the water temperature became below 10℃. This species is known to have strains that produce cylindrospermopsin toxic to liver, and saxitoxin that causes paralytic shellfish poisoning. Therefore, it is necessary to confirm the toxicity of this species that occurred in Lake Biwa and its surroundings, and to pay attention to its trends.

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