Visitors to central Sydney over the past 10 days have been asked to remain vigilant for possible symptoms of Legionnaires' disease.
Three women and four men, aged between 20 to 70, visited several locations in Sydney's central business district over the past 10 days and later developed symptoms of the disease.
New South Wales' officials issued a health warning on Wednesday after detecting the seven cases over the past three weeks.
All seven have been hospitalised, said NSW Health, the state's Ministry of Health.
Legionnaires' is a form of pneumonia caused by legionella bacteria, but it can't be spread between people.
Many of those with the disease don't develop symptoms, but those at-risk - including the immunocompromised and smokers - may do.
Symptoms include fever, chills, cough, muscle aches, diarrhoea, shortness of breath and potentially pneumonia.
The legionella bacteria that cause the disease live in soil, compost and potting mix, but also rivers, lakes and reservoirs.
They're often linked to contaminated cooling towers in large buildings, or people gardening without proper protection like masks.
People can get the disease by inhaling evaporated water droplets contaminated with legionella bacteria, such as from a cooling system.
NSW Health is working with the City of Sydney Council to inspect cooling towers in a bid to determine the cause of the recent cases. Authorities will also review maintenance records, it was reported, and contact the managers of relevant buildings.
