New York City Outbreak: What Is Legionnaires' Disease?

cooling towers
cooling towers (Image credit: feiyuezhangjie/

At least seven people in New York City have died and 86 have been infected in an outbreak of Legionnaires' disease. The illness can cause high fevers and pneumonia.

But despite the current outbreak, most people in the region aren't at any increased risk of getting Legionnaires'. The disease is not communicable between people, and only those with weakened immune systems or other health impairments tend to fall ill. In addition, most people who do get Legionnaires' can be treated with antibiotics.

From its source to its treatment, here are some of the most important things to know about the disease and the current outbreak. [5 Things You Should Know About Legionnaires' Disease]

1. What is Legionnaires' disease?

The disease is caused by a genus of bacteria known as Legionella, which lives in watery environments. The bacteria's natural hosts are other single-celled organisms such as amoebae. However, occasionally these bacteria may infect people, and can cause cough, high fever, pneumonia and death, said Dr. Victor Yu, a researcher at the Special Pathogens Laboratory at the University of Pittsburgh.

2. Is there treatment?

Yes. Legionnaires' disease can be treated effectively with antibiotics. Without treatment, the disease can kill up to 40 percent of the people who come down with symptoms, Yu said. But if the disease is caught and treated early, the mortality rate plummets to less than 5 percent, he added.

3. Who is at greatest risk of Legionnaires' disease?

In theory, anyone can catch the disease, but in reality, Legionnaires' typically sickens the elderly or those with weakened immune systems, such as transplant patients or individuals with diabetes, said Janet Stout, a microbiologist and the director of the Special Pathogens Laboratory.

"It essentially infects older people, and the most common are elderly men who smoke cigarettes," Yu said.

In the current outbreak in New York, everyone who has fallen ill had some underlying medical condition or health problem, according to the New York City Department of Public Health.

4. When was Legionnaires' disease first identified?

It was first identified in 1976, after a large number of people — mostly men who belonged to the veterans' organization the American Legion — fell ill after attending a convention at the Bellevue-Stratford Hotel in Philadelphia. Epidemiologists eventually identified the bacterial strain as the responsible culprit. The bacteria were found in the hotel's air conditioning system.

5. How is it spread?

Legionella cannot be passed between people. Instead, people become infected by inhaling mist or water droplets that are contaminated with the bacteria.

"The majority of cases of Legionnaires' disease occur as a result of the warm water system," Stout said.

The most common sources of outbreaks are drinking water systems in hospitals, hotels and other institutional facilities, she said. In those instances, people typically acquire the infection after breathing in a little bit of fluid, such as can happen when drinking something or taking a shower. Nowadays, more and more hospitals sanitize their water to prevent the spread of Legionnaires' disease, Yu said.

Most of these outbreaks last a long time, but involve only a few sporadic cases.

But when "explosive" outbreaks hit many people at once, water-cooling towers are often the culprits, Stout said. The current New York City outbreak is just such an explosive outbreak, as was a 2012 outbreak in Quebec City, Canada, that sickened 170.

"These devices provide Legionella bacteria with everything they need to grow," Stout said. The towers provide a warm, wet environment, while filters suck in dirt from the environment that provides perfect food for the bacteria to multiply. The towers also give off an aerosolized mist that can transmit the disease to people passing by, she added.

In one unusual case, people contracted the disease from the water-mist devices that are used to keep produce fresh at the supermarket, said Dr. William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center in Nashville, Tennessee.

6. What is the cause of the current outbreak in New York?

Officials have said that five water-cooling towers in the Bronx have tested positive for Legionella, and have since been decontaminated. However, it is common for water sources to test positive for Legionella, so the test result does not definitively point to these towers as the culprit of an outbreak, Yu said. For instance, 30 to 70 percent of three-story apartment buildings may test positive for Legionella, but do not necessarily cause disease, he said.

To be sure that the cooling towers were indeed the source of the New York outbreak, researchers will need to test the molecular fingerprint of the bacteria from patients, and compare it with environmental samples from the cooling towers. That should take about a week, Stout said.

7. Can officials stop the current outbreak?

Yes. Legionella is resistant to chlorine, but other methods of sanitizing the systems, such flushing superheated water through the system, or using copper-silver ionization, can kill the bacteria, Yu said.

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Tia Ghose
Managing Editor

Tia is the managing editor and was previously a senior writer for Live Science. Her work has appeared in Scientific American, and other outlets. She holds a master's degree in bioengineering from the University of Washington, a graduate certificate in science writing from UC Santa Cruz and a bachelor's degree in mechanical engineering from the University of Texas at Austin. Tia was part of a team at the Milwaukee Journal Sentinel that published the Empty Cradles series on preterm births, which won multiple awards, including the 2012 Casey Medal for Meritorious Journalism.