What Is Legionnaires' Disease? Outbreak Kills Two

Nearly 60 have become ill in a New York City outbreak

Kristen Fischer,

AARP

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Published August 05, 2025

An outbreak of Legionnaires' disease in New York City is caused by the bacteria Legionella pneumophila.

James Cavallini/Science Source

An outbreak of Legionnaires’ disease in New York City has infected at least 58 people and killed two, the NYC Health Department reports.

This might put you on edge if you’re near the epicenter or you aren’t feeling well. While the disease is treatable, older adults are more vulnerable to it, so it’s good to be informed.

Legionnaires’ disease is a serious form of pneumonia caused by Legionella bacterium.

People older than age 50 and those with diabetes, kidney failure, cancer, lung disease or a weakened immune system are at higher risk, according to the Centers for Disease Control. Those in long-term care facilities, including nursing homes, can be especially prone to infection because those spaces likely have the large water systems that can become contaminated.

What is Legionnaires’ disease?

Legionnaires’ disease is the “lung manifestation” or pneumonia that’s caused by Legionella bacterium, says Jin Suh, M.D., chief of infectious disease at St. Joseph’s Health in Paterson, New Jersey.

Pontiac fever, a less serious illness caused by the same bacteria can lead to flu-like symptoms such as fever or muscle ache.

In rare cases, Legionella can infect other parts of your body outside of the lungs, such as in the heart and brain, or by way of skin infections, Suh says.

What causes Legionnaires’ disease?

Legionella bacterium naturally occurs in lakes, streams and soil. It’s an environmental pathogen, Suh says. There’s typically not enough bacteria in natural environment to cause illness.

The bacterium can contaminate drinking water and air systems, which is where the bacteria can multiply and lead to outbreaks. It can also grow in sink faucets, shower heads and hot tubs at home. You can get also Legionnaires’ disease through aspiration, or when something goes down the wrong pipe, but that’s not as common.

Mohamed Hamdy Yassin, M.D., an infectious disease specialist with University of Pittsburgh Medical Center who sees about 15 to 20 cases of Legionnaires’ disease each year, says the infection doesn’t always come from large buildings. Most cases he has seen come from a problem with a home’s water system. If your home water system has problems, or hasn’t run in a while, the bacterium can build up to harmful levels.

“It’s not uncommon to see people living in areas where their water system is not very well maintained,” Yassin says, and those people are at higher risk for the disease.

Another cause for infections is in people who own a second home where the water doesn’t run for months. (In that case, run your water for about 30 minutes before taking a shower or drinking the water, Yassin advises.)

There are at least 60 different strains of Legionella, though the majority of illnesses are caused by Legionella pneumophila, the CDC reports.

What are the symptoms of Legionnaires’ disease?

Legionnaires’ disease causes symptoms that can be mild or serious. The disease can feel like the flu or pneumonia, or include gastrointestinal or neurological symptoms. Symptoms usually begin two to 14 days after you’re exposed to the bacteria.

Common Legionnaires’ disease symptoms include:

Fever that often goes above 104 F
Cough (usually dry)
Headache
Shortness of breath
Nausea
Diarrhea
Muscle aches
Stomach pain
Confusion
Coughing up blood

Yassin says doctors call Legionnaires’ disease “summer pneumonia,” because outbreaks often happen in warm weather. The infection is more common between June and October.

“It’s very tricky,” he says, because symptoms can mimic other conditions. With Legionnaires’ disease, people often feel very sick beyond respiratory symptoms, Yassin adds.

Studies show that between 1 to 10 percent of pneumonias that come into a hospital caused by Legionella.

How is Legionnaires’ disease diagnosed?

Your health care professional will perform a chest x-ray or computer tomography (CT) scan to confirm if you have pneumonia.

How Legionnaires’ Got Its Name

The disease is named after an outbreak at an American Legion convention in Philadelphia in July 1976. Of the 182 Legionnaires who contracted the disease, 29 died. The strain of bacteria that causes the disease was later named Legionella.

You may need other tests to see if Legionella bacterium is causing the pneumonia. These include urine, blood and phlegm tests. Your doctor may conduct a bronchoscopy, which involves inserting a thin tube to see inside your lungs and collect samples. Or they may conduct thoracentesis, inserting a needle in your chest area to drain fluid from your lungs to check for Legionella.

Hospitals should test everyone with pneumonia for Legionella, but not every doctor does that, Yassin says.

If you don’t feel right, especially if you’re near the area of a confirmed outbreak, seek medical attention, Suh says. “Legionnaires’ is very treatable especially if you catch it early,” he adds.

How is Legionnaires’ disease treated?

Your doctor will likely prescribe an antibiotic either orally or intravenously. They may give you oxygen if you have trouble breathing; in severe cases, mechanical ventilation may be necessary. Expect to stay in the hospital while you’re being treated.

How many people get Legionnaires’ disease each year?

In recent years, it’s affected about 8,000 people annually. Between 2016 and 2022, people over the age of 40 contracted more than nine in every 10 cases. Adults 65 and older made up about half of all cases in 2022, the CDC reports.

Who’s most at risk for Legionnaires’ disease?

Most younger, healthy people won’t become ill from Legionella. Older adults have a higher risk for Legionnaires’ disease, as do those who:

Have weakened immune system
Respiratory illnesses like chronic obstructive pulmonary disease (COPD) or emphysema.
Live in a long-term care facility including nursing homes
Have had a recent hospital stay, recent organ transplant or recent surgery with anesthesia
Smoke or used to smoke cigarettes

Is Legionnaires’ disease serious?

Though infection with the bacteria can be life-threatening, it is generally treatable once you receive antibiotics.

Is Legionnaires’ disease contagious?

It’s not spread from person to person; you have to come into direct contact with the bacteria to get it.

What’s the prognosis?

Outcomes can vary if clinicians do not accurately pinpoint the cause of the pneumonia or prescribe the right antibiotic, Yassin says. People can die without timely care, he adds.

About one out of every 10 people who contracts Legionnaires’ disease will die due to complications from the illness. Among those who get it while staying in a health care facility, about one in four will die, the CDC reports.

In some cases, you may experience lingering symptoms after you’re discharged from the hospital. These can include muscle aches, trouble walking, issues with balance and coordinated, slurred speech and fatigue.

Those residual effects may need time to heal, and it doesn’t necessarily mean patients need more antibiotics, Suh says.

“There’s a lot of variability [with Legionnaires’ disease infections],” Suh says, adding that aftereffects aren’t just only in older adults.

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Kristen Fischer is a contributing writer at AARP based at the Jersey Shore. She has also written for Health, WebMD, and McKnights and is the author of Zoo Zen: A Yoga Story for Kids.