The Centre for Health Protection is investigating three cases of Legionnaires’ disease.
They involve three men aged 57 to 70.
The patients live in Sai Kung, Tseung Kwan O and Tai Po, and have underlying illnesses.
Fifteen Legionnaires’ disease cases have been reported so far this year.
There were 75 and 66 cases in 2016 and 2015.