Legionnaires' disease outbreak in Victoria

The Department of Health, Victoria has confirmed there are 77 cases and 7 suspected cases of Legionnaires’ disease (Legionellosis) in the state.

With most cases requiring hospitalisation, the department has reminded health professionals to have “a high index of suspicion for Legionnaires’ disease in patients with compatible symptoms, particularly community acquired pneumonia with risk factors”.

Victoria’s Chief Health Officer, Clare Looker, said the sites most frequently visited by cases are in the Laverton and Derrimut area and investigations suggest the source of the outbreak is one cooling tower in this area.

Identifying the culprit

Associate Professor Sanjaya Senanayake, a specialist in Infectious Diseases and Associate Professor of Medicine at The Australian National University, said, “Legionella is an environmental bacterial infection that causes pneumonia (a lung infection). It tends to be more severe in older people, smokers and those with chronic lung and kidney disease. Unfortunately, it can be fatal, especially in these groups.

“Legionella likes living in warm water (25–45 degrees C) such as can be found in cooling towers. This is why cooling towers require mandatory periodic testing for the presence of Legionella.

“Two positives about Legionella are that it can’t be transmitted between people and that commonly used antibiotics are effective against it.

“The public health investigation will be trying to identify the culprit cooling tower, which will likely involve a combination of epidemiological studies of cases and uninfected controls, as well as testing of cooling towers in the suspect areas.”

Weather conditions and outbreaks

Dr Verlaine Timms, a Senior Research Fellow at the Neilan Laboratory of Microbial and Molecular Diversity at the University of Newcastle, said that in many cities, Legionnaires’ disease cases peak during autumn and summer, often following periods of high rainfall and humidity.

“Globally, the incidence of Legionnaires’ disease has increased significantly, with notable rises in the USA and Hong Kong. This increase may be due to a growing number of susceptible individuals, better diagnostic methods and improved reporting,” Timms said.

The disease is more frequently diagnosed in men over 50, particularly smokers or those with underlying health conditions, Timms said.

“Our research focused on how Legionella pneumophila spreads in urban environments and explored the relationship between weather conditions and Legionnaires’ disease outbreaks. Interestingly, while increases in humidity and rainfall are linked to a rise in Legionnaires’ disease cases, the major outbreak clones of L. pneumophila did not show a direct connection to weather changes in our study.

“These findings highlight the importance of high-resolution bacterial typing (genome sequencing) and considering weather data when investigating Legionnaires’ disease outbreaks, especially when clinical samples are limited. This approach can help improve strategies for managing and preventing Legionnaires’ disease in urban areas.”

Minimising risks

Dr Adriana Milazzo, a Senior Lecturer in the University of Adelaide’s School of Public Health, noted that air conditioner cooling towers have been implicated in outbreaks previously, as have aerosol-producing devices such as spa baths/spa pools, water misters and decorative fountains.

“To minimise the risk of growth of Legionella in cooling towers, they should be properly maintained and monitored.

“People of any age may be infected, though the disease is more common in older people and people with weakened immune system.”

However, the risk of infection is increased by smoking, chronic lung or heart disease, diabetes, some forms of cancer and immunosuppression, Milazzo said.

Recommendations for clinicians

The Department of Health, Victoria, has made the following recommendations for clinicians:

Consider Legionnaires’ disease in patients presenting with compatible symptoms who live in, work in or have visited metropolitan Melbourne and surrounding areas. When suspecting Legionnaires’ disease, request urgent urinary antigen testing through normal pathology provider. As a priority, order Legionella culture and PCR (eg, an ‘atypical pneumonia PCR’ panel) on sputum or other respiratory fluid samples (eg, bronchial washings, endotracheal aspirates). Serology can be requested on blood at symptom onset and three to six weeks later (as convalescent serology). Early diagnosis and treatment with appropriate antibiotics are important. Refer to the current edition of the Therapeutic Guidelines for treatment guidelines or consult with local infectious diseases service. Legionnaires’ disease is an urgent notifiable condition that must be notified to the Department of Health upon initial diagnosis or clinical suspicion as soon as practicable and within 24 hours by calling 1300 651 160 and connecting to the relevant Local Public Health Unit.

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