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<\/p>\nIn July 1976, thousands of veterans gathered for a meeting of the American Legion at the Bellevue-Stratford Hotel in Philadelphia.<\/p>\n
A few days later, a retired US Air Force captain died of an apparent heart attack.<\/p>\n
Within a week, another eight men were dead. More were sick with fevers, shortness of breath and chest pains.<\/p>\n
“This was big news that these war veterans were being sickened,” says Robert Promisloff, a clinical professor emeritus of medicine at Drexel University in Philadelphia.<\/p>\n
The disease came to be called Legionnaires’ disease, after the American Legions who fell ill.<\/p>\n
Fifty years on, cases of the deadly disease appear to be rising around the world, and experts are not certain why.<\/p>\n
The first outbreak<\/p>\n
Professor Promisloff was training to become a lung specialist at Philadelphia’s Hahnemann University Hospital when the first outbreak occurred.<\/p>\n
“We were all scratching our heads,” Professor Promisloff says.<\/p>\n
“Nobody really knew what was going on.”<\/p>\n
Patients were admitted with pneumonia, but the usual antibiotics weren’t working.\u00a0<\/p>\n
“That was extremely difficult \u2026 watching people get sicker and sicker,” Professor Promisloff says.<\/p>\n
In total, 182 people fell ill and 29 died.<\/p>\n
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More than 2,000 members of the American Legion attended the conference at the hotel. (Supplied: US Library of Congress)<\/p>\n
The US Centers for Disease Control and Prevention (CDC) launched an investigation.<\/p>\n
Experts knew the Bellevue-Stratford Hotel was at the centre of the outbreak, but they struggled to pinpoint the source.<\/p>\n
Was it something the attendees ate? Were only certain rooms affected? The CDC even tested cigarettes given to participants in their conference materials.<\/p>\n
“There were people picketing in front of the hospital, handing out leaflets that it was a government plot to kill people,” Professor Promisloff says.<\/p>\n
“Some newspapers were calling it a hoax. They were blaming the government. They were blaming the communists.”![\"Clippings](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2026\/10\/9e227e5ce640150c749a9aea0bf93622.jpeg\")
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Conspiracy theories emerged as authorities struggled to find the cause of the deadly pneumonia. (Supplied: US CDC)<\/p>\n
A lucky discovery<\/p>\n
Meanwhile, CDC microbiologist Joseph McDade was trying to work out what caused the disease.<\/p>\n
He had noticed occasional rod-shaped bacterium in lung samples taken from patients, but not enough to raise alarm bells.<\/p>\n
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Joseph McDade isolated and identified the bacterium that causes Legionnaires’ disease. (Supplied: US CDC)<\/p>\n
Dr McDade started looking for a virus instead, using antibiotics to knock out the rods “contaminating” the samples.\u00a0<\/p>\n
Six months on, he still hadn’t found the culprit.<\/p>\n
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Legionnaires’ disease was also called the “Philly Killer” when the outbreak began. (Supplied: US CDC)<\/p>\n
Around new year’s, Dr McDade visited his lab to declutter and decided to look at the samples again.<\/p>\n
This time, instead of seeing a single rod-shaped bacterium, he saw a cluster he named Legionella pneumophila.<\/p>\n
It took further outbreaks to discover the likely source of the Philadelphia outbreak was the hotel’s water cooling tower that fed its air conditioning system.<\/p>\n
Legionella lives in soil and water, and is known as an “accidental” pathogen because it doesn’t need to infect humans to survive.<\/p>\n
The bacteria are found globally in natural waterways in low concentrations, but causes problems when concentrated in human-built infrastructure.<\/p>\n
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It took six months for a CDC scientist to identify the bacteria responsible for Legionnaires’ disease, which appears here in multiple circular and rod-shaped clusters. (Supplied: US CDC \/ Martin D Hicklin)<\/p>\n
“If [Legionella] is in high numbers in a water cooling tower, and someone who’s vulnerable breathes in the aerosol, it can colonise the lung,” says Verlaine Timms, a microbiologist at the University of Newcastle and University of Western Sydney.<\/p>\n
Most healthy people won’t get sick. But it can affect people with weakened immune systems, such as older people and smokers, unless it’s treated with specific antibiotics.<\/p>\n
Australia’s biggest outbreak<\/p>\n
Australia’s first-known case of Legionnaires’ disease occurred in 1979, just a few years after the bacteria was discovered.<\/p>\n
But the country’s biggest outbreak happened in April 2000.<\/p>\n
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At the time, Jane Greig was training to become an epidemiologist.<\/p>\n
She had been in Melbourne only a few months when Victoria’s health department was notified that four people had contracted Legionnaires’ disease.<\/p>\n
All of them had visited the recently opened Melbourne Aquarium.<\/p>\n
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Melbourne Aquarium was at the centre of a Legionnaires’ outbreak in April 2000. (ABC News)<\/p>\n
“I was in the office of my field supervisor when someone came in to tell him they were going to send an investigation team to the aquarium, and I was offered, ‘Do you want to go along?'” Dr Greig recalls.<\/p>\n
The team took samples from all the fish tanks, but strongly suspected the aquarium’s water cooling towers.<\/p>\n
Days later, samples from the cooling towers tested positive<\/a> for Legionella.<\/p>\n The health department set up a 1300 telephone number for concerned members of the public.<\/p>\n “That took over the boardroom on our floor of the department, and there was maybe 10 staff at any one time taking calls well into the evening,” Dr Greig says.<\/p>\n In total, 125 cases were confirmed, and four people died.<\/p>\n Melbourne Aquarium stopped using water cooling towers as part of its air conditioning system. (ABC)<\/p>\n After the 2000 outbreak, the Victorian government introduced stricter rules<\/a> on water cooling towers, bringing it in line with New South Wales, which had cracked down in response to major outbreaks years earlier in Wollongong and Fairfield.<\/p>\n Regulations differ across Australia’s states and territories, but typically involve installation requirements and regular inspections.<\/p>\n Cases on the rise<\/p>\n Although we now know the culprit, Legionnaires’ disease has surged over the past three decades.<\/p>\n New York is currently dealing with its second deadly outbreak<\/a> this year. Eleven people died in the first cluster, and the latest outbreak has killed two.<\/p>\n Australia has so far avoided a major outbreak in 2026.<\/p>\n But data suggests cases are trending up, particularly in NSW and Victoria.<\/p>\n “There’s a couple of reasons that people believe contribute,” Dr Timms says.<\/p>\n Big buildings like offices and hospitals typically use cooling towers in their air conditioning systems. As cities get bigger, the number of water cooling towers increases.<\/p>\n Australia also has an aging population that’s more likely to fall ill after inhaling Legionella.<\/p>\n Climate change has also been suggested as an explanation, given the bacteria thrives in wet, humid places.<\/p>\n![\"Zoom](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2026\/10\/84fc014a75fa13e222a40212a9b4d170.jpeg\")
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