The Centre for Health Protection is investigating a case of Legionnaires' disease involving a 37-year-old man living on the Mainland.
He fell ill on April 30 and came to Hong Kong on May 2 and was admitted to North District Hospital.
He was later transferred to Queen Elizabeth Hospital and was admitted to the intensive care unit yesterday.
He was diagnosed as having pneumonia and is now in critical condition.
Tests found he was suffering from Legionnaires' disease.
The patient's home contact has no symptoms.
It is the 11th case reported this year. There were 41 cases last year and 28 in 2013.
