The Centre for Health Protection is investigating three cases of Legionnaires’ disease.
They involve three men aged 54 to 75. Two have underlying illnesses.
The patients live in Kwun Tong, Tai Wai and Ap Lei Chau.
Forty-nine Legionnaires’ disease cases have been reported so far this year.
There were 75 cases in 2016 and 66 in 2015.