Legionnaires’ disease: more cases likely as health authorities search for source of Sydney outbreak | Legionnaires’ disease

People who have visited Sydney’s CBD over the past 10 days have been warned to be alert for symptoms of legionnaires’ disease.

NSW Health says seven people who developed the disease spent time in the city over the past three weeks. More cases are expected.

But what is legionnaires’ disease, how can you catch it, can it be fatal and what caused this outbreak?

What is legionnaires’ disease?

Legionnaires’ disease – named after an outbreak at a conference of American Legionnaires in 1976 – is a form of pneumonia, or lung infection, caused by legionella bacteria.

The bacteria can be found in damp environments and, in Australia, the two most common types are found in water and soil.

Legionnaires’ disease is a notifiable disease – meaning doctors must tell NSW Health if a patient tests positive.

What are the symptoms?

Symptoms include fever, chills, a cough and shortness of breath. Some people may also have muscle aches, headaches, tiredness, loss of appetite and diarrhoea.

Legionnaires’ disease may lead to severe chest infections such as pneumonia. It can also affect the liver, kidneys or heart. Most people recover but the disease is occasionally fatal, according to NSW Health.

Richard Bentham, an associate professor from Flinders University, says legionnaires’ disease is fatal for about 10% of people who contract it. However, those who develop the disease are a susceptible subgroup of the general population.

“Most people who are exposed to the bacteria won’t show any symptoms at all, or they [might] show mild symptoms, feel a bit off for a couple of days and get over it,” Bentham says.

Those at highest risk of contracting the disease are smokers, people over 50, those with existing chest or respiratory disease and immunocompromised people.

Can we expect more cases?

Prof Mark Ferson from the public health unit at the South Eastern Sydney Local Health District suggests more cases could be announced imminently.

Given it’s still the incubation period for the current cluster, Bentham says it “wouldn’t be surprising” if a few more cases appeared in people who don’t yet know they’ve been infected.

“[But] I would expect there wouldn’t be many more cases after another five to seven days.”

How do you catch it?

People can contract legionnaires’ disease by breathing in contaminated dust or water vapour. NSW Health says the disease is not spread from person to person.

There are only a few cases in the legionella literature regarding possible transmission between people, with the general view being it is not a transmissible disease, Bentham says.

Symptoms can develop up to 10 days from the time of exposure to contaminated water particles in the air.

Who contracted it and where?

In the current outbreak, seven people have been identified with the legionella bacteria that causes legionnaires’ disease – three women and four men ranging in age from their 20s to their 70s.

They independently visited locations in the Sydney CBD between Bathurst Street, Sussex Street, Elizabeth Street and Circular Quay in the 10 days before developing symptoms.

They have all been admitted to hospital for the treatment of pneumonia.

What is the source of the Sydney cluster and what’s being done about it?

The legionella bacteria are often associated with contaminated cooling towers of large buildings. These work to cool buildings by recirculating water through a heat exchanger.

Air comes into the cooling tower from outside – bringing dust and dirt which acts as food for bacteria. Cooling towers operate at about 25C to 30C when warming water.

“So basically the bacteria find themselves in a nutrient-filled incubator,” Bentham said.

The current Sydney cluster could be attributed to the Christmas break when some buildings shut down. The cooler weather also means air conditioning could be turned off.

“If the cooling towers [are] turned off and left off for a while, the legionella grows in that slime; the slime detaches, then when it is turned on, a big flush of bacteria suddenly goes into the cooling tower and goes out in a drift, and that may happen before the chemical treatment can get to them and treat them,” Bentham says.

Cooling towers generate a fine mist – or aerosol – which is released into the air and can be inhaled into the lungs. This is how people can contract the disease.

NSW Health environmental health officers are working with the City of Sydney to inspect cooling towers. A review of maintenance records “will also help determine further towers to be inspected and sampled”, the department says.

Managers of buildings with cooling towers are being contacted and asked to ensure they are operated and maintained correctly.

Ferson says there are various enforcement mechanisms NSW Health can use if cooling towers are not operating correctly – including improvement notices with fees.

It takes five to seven days for a laboratory to grow the legionella bacteria and determine whether a cooling tower is contaminated.

Can the cluster be linked to a specific cooling tower?

NSW Health says a cooling tower that is the source of an outbreak may not be identified despite careful investigations. That’s because it could be transiently contaminated by bacteria floating through the air and the cooling tower’s regular cleaning processes may decontaminate it – even before infected patients are diagnosed.

How is legionnaires’ disease treated?

People can be diagnosed with legionnaires’ disease by a urine or sputum test and a chest X-ray. They usually require antibiotic treatment in hospital.

For serious infections, patients may be treated in the intensive care unit and have their breathing assisted using a ventilator.

Should people be wearing masks?

NSW Health is not advising people in the Sydney CBD to wear masks – but instead remain on the lookout for any symptoms.

Bentham says wearing a mask “wouldn’t be a bad idea” for those most at risk until the outbreak is over.

“They will provide some protection,” he says. “The sort of masks that we wear around the street won’t stop aerosol but will reduce the amount of aerosol getting into the lungs and [help prevent] people getting sick.”

Why do these outbreaks happen and can we stop them?

The only real way to manage the spread of legionella bacteria into the community via cooling towers is continual maintenance, experts say.

“If they are well managed, legionella is well controlled and there aren’t cases of legionnaires’ disease but … that doesn’t always happen,” Bentham says.

“Because [cooling towers sit] on the roof just providing air conditioning, they tend to get a bit forgotten.”

There are Australian standards for designing and maintaining cooling towers as well as regulations in NSW. The latter includes monthly checks and sampling for bacteria, including legionella. The health department can also conduct random inspections.