The Centre for Health Protection is investigating a case of Legionnaires' disease affecting a woman aged 87 who is in stable condition.
The patient, with underlying illness, has developed a fever, cough, shortness of breath and muscle pain since June 23.
She visited a private hospital out-patient department on June 25 and was admitted the same day.
She was diagnosed with pneumonia, but tested positive for the Legionella pneumophila serogroup 1 antigen.
The patient had no recent travel history and her home contacts have no symptoms.
It is the 21st Legionnaires' disease case reported this year. There were 41 cases last year and 28 in 2013.
