Health authorities are racing to find the source of an outbreak of legionnaires' disease that is expected to grow over coming days.
The majority of the 33 patients with the severe form of pneumonia have been admitted to hospital and at least six are in intensive case.
Test results for a further 10 people suspected of having the disease are due back soon and the number of patients is expected to rise.
Victorian chief health officer Clare Looker said the source of the outbreak was yet to be confirmed but she believed it to be a single cooling tower in metropolitan Melbourne.
"These numbers that we're seeing at the moment are much greater than the usual three to six that we see a week so we think most cases are from a single source," Dr Looker told reporters on Tuesday.
Eighteen cooling towers at public venues, factories and industrial sites have so far been disinfected.
People struck down by the illness have visited or lived in a variety of suburbs across Melbourne and there was no evidence yet that they all visited a single site, but a lot of patients crossed over in the city's north and west.
Most patients are male, aged over 50 and live or work in metropolitan Melbourne.
No cases have been detected in children, who do not typically contract the disease.
Legionnaires' disease is caused by the legionella bacteria, which is found in natural bodies of water as well as spas, warm water systems, potting mix and artificial systems that use water for cooling.
Symptoms usually include a chest infection, aches, headache, fever, cough and chills.
People with underlying diseases, particularly those who are immunocompromised, elderly people and smokers are at greater risk of infection.
