What is Legionnaires' disease and how do you get it? Here's what you need to know about the illness. (Pamela Kirkland/The Washington Post)

Officials are investigating after a New York Police Department officer contracted Legionnaires' disease, a potentially life-threatening form of pneumonia.

Preliminary test results indicate that traces of the bacteria causing Legionnaires' disease were found at the police station in East Harlem. Officials have started inspecting the facility's systems and testing the precinct's water supply. The officer, who was not named, is recovering at a hospital outside of the city, according to the New York City Department of Health.

Officials first became aware of the situation Saturday.

Legionnaires' disease is treatable with antibiotics, but it can be deadly if left untreated. Legionella pneumophila, the type of bacteria that causes the disease, thrive and multiply in water systems, cooling towers, indoor plumbing, hot tubs, air conditioners and mist sprayers. Most outbreaks have occurred in large buildings because complex water systems allow the bacteria to grow and spread more easily, according to the Mayo Clinic.

“Health officials are on site today to sample water in indoor plumbing, and to provide additional assistance and guidance,” the health department said in a statement Sunday. "Legionnaires' disease is not contagious, officers can still work in the building but should avoid taking showers at the site until the investigation is complete. There is no public health risk to the larger community."

The hot water supply at the station has been temporarily shut down.

Officials have ruled out a cooling tower that supports the facility's heating, ventilation and air conditioning systems as a possible origin of the bacteria because it has been shut down since October as part of a renovation project, according to the police department. A new tower was installed last month, but it has not been activated.

Legionnaires' disease was first discovered in 1976, when people attending a Pennsylvania American Legion convention at a hotel in Philadelphia developed pneumonia. More than 200 convention attendees and visitors were infected, and some died.

People get sick with Legionnaires' disease by breathing small droplets of water containing the bacteria. Symptoms include headache, muscle pain, chills, fever, cough, shortness of breath, chest pain, nausea, vomiting and diarrhea. Those at risk of getting sick are adults 50 years or older, smokers, and people with a chronic lung disease, weak immune systems, cancer and other preexisting illnesses, according to the Centers for Disease Control and Prevention.

On Friday, two guests at a Las Vegas resort contracted Legionnaires' disease, according to media reports. One stayed at the Rio All-Suite Hotel and Casino in March, while the other stayed there in April, CNN reported. Health officials said Legionella was found in the hot-water system of one of the hotel's towers.

Between 200 and 400 cases of Legionnaires' disease are reported in New York City every year, according to the health department.

In 2015, an outbreak in the South Bronx prompted health officials to implement tougher cooling tower regulations, hire more inspectors and train city employees on how to inspect cooling towers, officials said.

Federal officials said last year that cases of Legionnaires' disease have nearly quadrupled in the United States over a 15-year period. About 6,000 cases were reported in 2015 alone.

“Large recent outbreaks in New York City and Flint, Mich., have brought attention to the disease and highlight the need to understand why the outbreaks occur and how best to prevent them,” Tom Frieden, then the CDC's director, said in a briefing last year.

Infants born during water births are at risk of contracting the disease.

Two infants in Arizona were infected with Legionnaires' disease in 2016, according to the CDC. Both were delivered by a midwife in a home birthing tub. They survived after receiving antibiotics.

Lena H. Sun contributed to this story.

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