The Centre for Health Protection is investigating a case of Legionnaires' disease involving a 90-year-old man who is in critical condition.
He fell ill on October 7 and was admitted to Queen Elizabeth Hospital on October 9.
Tests revealed that he was suffering from Legionnaires' disease.
This is the 33rd case of the disease reported to health authorities this year.
There were 28 cases both in 2013 and 2012.