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.

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by Tia Ghose, Senior Writer   |   August 05, 2015 12:22pm ET
Live Science