The Centre for Health Protection is investigating five cases of Legionnaires' disease.
They involve five men aged 61 to 82. All have underlying illnesses.
They live in Yuen Long, Tai Po, Kwai Chung, Tseung Kwan O and Yau Yat Tsuen.
One of the men as well as another patient reported last month both live in Ho Ming Court, Tseung Kwan O.
Fifty-nine Legionnaires' disease cases have been reported so far this year.
There were 75 and 66 cases in 2016 and 2015.
