Health authorities are testing dozens of cooling towers in Melbourne's CBD after eight confirmed cases of legionnaires' disease.
The number of patients infected is almost triple that from a week earlier, and a ninth case is also suspected, Victoria's Deputy Chief Health Officer Dr Brett Sutton said on Wednesday.
Six men and three women have been hospitalised, and two placed in intensive care.
All patients fell ill within a two-week period earlier in February after visiting the CBD.
The Department of Health and Human Services is working to confirm whether the cases are linked to contaminated cooling towers in the southeast of the city.
More than 70 cooling towers have been tested, and another 34 are undergoing sampling and disinfection.
People can become infected with legionnaires' disease after breathing in contaminated droplets of water, and those aged over 50, who smoke, drink or who have conditions such as diabetes and chronic lung disease are particularly vulnerable.
"People who have visited the CBD between late January and mid-February and who may be suffering from pneumonia or flu-like symptoms should see their GP, who will assess the need for testing for legionnaires' disease," Dr Sutton said.
