Building owners in Sydney are being asked to check their water cooling towers after four new diagnoses of legionnaires' disease.
No source for the four infections has been identified but all those affected visited Sydney's CBD during January.
The four cases are from a strain most commonly associated with cooling towers.
NSW Health has asked building owners and tenants to check their towers are well maintained.
The department in 2018 strengthened regulations which now require building owners to conduct monthly tests and notify local councils of high levels of bacteria including legionella.
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Health Protection executive director Jeremy McAnulty says the disease can't spread from person to person.
"Symptoms can develop up to 10 days from the time of exposure to contaminated water particles in the air," Dr McAnulty said in a statement on Wednesday.
"People who develop this disease are diagnosed by chest X-ray and a urine test and usually require antibiotic treatment in hospital."
The disease may lead to severe chest infections such as pneumonia and symptoms including fever, chills, a cough and shortness of breath.
