The Centre for Health Protection is investigating two cases of Legionnaires' disease affecting a man and a woman.
Both patients have underlying illnesses.
The 86-year old woman lives at 144 Kwong Fuk Road, Tai Po, while the 72-year-old man is a resident of Tsui Wing House, Tsui Ping (South) Estate, Kwun Tong.
Four Legionnaires' cases have been reported so far this year. In 2015 and 2014, there were 66 and 41 cases.
