A significant outbreak of Legionnaires' disease has emerged in metropolitan Melbourne, with at least 22 confirmed cases and six suspected cases reported since Friday.

All confirmed cases are linked to metropolitan Melbourne, where affected individuals either reside or have visited.

The outbreak is attributed to the Legionella pneumophilia serogroup 1 bacteria, commonly found in water systems such as cooling towers, spas, and natural bodies of water.

Health authorities are actively investigating the outbreak's source, focusing on local cooling towers and other potential sources of the bacteria.

Dr. Sarah McLean noted that cooling towers are regulated under public health legislation in Victoria, and control measures are being implemented.

Most affected individuals are adults over 40, particularly those with preexisting medical conditions or compromised immune systems, many of whom require hospitalization for severe pneumonia.

While most people recover from Legionnaires' disease, about 10% of those infected may die, underscoring the seriousness of the outbreak.

Residents are urged to seek medical attention if they experience symptoms such as fever, chills, cough, or muscle aches, especially those in high-risk groups.

Legionnaires' disease is primarily contracted by inhaling contaminated dust or water vapor, and is not spread through person-to-person contact.

Symptoms of the disease include fever, chills, cough, and general malaise, prompting immediate medical attention.

Chief Health Officer Dr. Clare Looker has indicated a rise in case numbers following an increase in hospital presentations since the outbreak began.

Health Minister Mary-Anne Thomas expressed concern that authorities have yet to identify the outbreak's source, emphasizing the need for vigilance.