“The Japanese Guideline for Prevention of Legionellosis” will be introduced and the status
of Legionella inhibition in cooling water systems in Japan will be discussed. About 9,000 sampling
data on Legionella in cooling water systems will be discussed. Seasonal trend was observed by
cooling water sample number and Legionella positive ratio. Moreover, positive ratio with registered
chemical treatment program at “the Japanese Association of Air Conditioning Water Treatment
Chemicals for Legionella“ was about half that without chemical treatment. It is concluded that
registered chemical treatment program is successful in Japan.