What Is Legionnaires' Disease? Potentially Fatal Illness Hits 27 in Manhattan

New York City officials are currently investigating 27 cases of Legionnaires' disease in Manhattan, the New York City Department of Health and Mental Hygiene reported.

Case numbers have risen in recent weeks in an area of lower Washington Heights, following the diagnosis of eight people in early July.

Legionnaires' disease is a type of pneumonia caused by exposure to Legionella bacteria. These bacteria thrive in warm water and can grow and spread in water systems like showerheads, air-conditioning cooling towers and hot water tanks, according to the CDC.

People who breathe in water vapor containing Legionella can experience symptoms including fever, coughing and muscle aches. However, most people who come into contact with the bacteria don't get sick.

People age 50 or older are at a higher risk of illness, as are smokers and those with weak immune systems, cancer, chronic lung disease and other underlying health conditions, according to the CDC.

Most people with Legionnaires' need to be treated in a hospital. In rare cases, the disease can prove fatal, but the vast majority of people receiving proper treatment return to full health.

The disease isn't normally considered contagious, but the health agency stated that human-to-human transmission "may be possible under rare circumstances."

"While most people exposed to Legionella don't get sick, individuals aged 50 and above, especially those who smoke and have chronic lung conditions, are at a higher risk," said NYC health commissioner Mary T. Bassett in a statement released earlier this month. "This disease is very treatable with antibiotics. I encourage anyone with symptoms of Legionnaires' disease to seek care early."

Symptoms of #Legionnaires' disease include fever, cough and muscle aches. The disease is easily treatable when caught early. The facts: https://t.co/prnGYyaxXt pic.twitter.com/6sdmJ0FuNH

— nychealthy (@nycHealthy) July 29, 2018

Meanwhile, routine testing revealed the presence of Legionella bacteria in the water supply of a hospital in the Bronx.

"Routine, required testing of our potable water supply found very low levels of Legionella bacteria at NYC Health + Hospitals/Jacobi," said a hospital statement shared with ABC 7. "Per guidance from the New York State Department of Health, which regulates hospitals, we have taken steps to prevent any impact on our patients, staff or visitors."

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The risk to staff, patients and visitors at Jacobi Medical Center was low, officials told the outlet, and no patients at the hospital appeared to have developed Legionnaires' disease.

7_30_Water cooling system
A cooling tower of a large air-conditioning system. Such systems were linked to Legionnaires' disease outbreaks in the past. Getty Images

New York City saw a deadly outbreak of Legionnaires' in 2015 that affected hundreds of people and killed 16, according to the CDC. Investigators eventually traced the outbreak to a hotel's cooling tower.

The New York City Health Department did not immediately respond to a request for comment.