Legionnaires' disease is a severe form of pneumonia caused by...

Legionnaires' disease is a severe form of pneumonia caused by a type of bacteria called Legionella, according to the CDC. This colorized scanning electron micrograph with moderately-high magnification depicts a large grouping of Gram-negative Legionella pneumophila bacteria. Credit: Wikimedia Commons / CDC

At least 57 people in New York City have been infected with Legionnaires' disease, and three have now died from the infection, Mayor Bill de Blasio's office said Friday afternoon.

The outbreak's tally was an increase from a day earlier, when 46 had been reported infected and two reported dead.

The latest death, of a middle-aged man who like the other fatalities had pre-existing medical ailments, occurred late Thursday, mayoral spokesman Peter Kadushin said.

He said that 42 of the 57 people diagnosed since July 10 -- the apparent start of the latest cluster -- were hospitalized, with 19 of those treated discharged.

The outbreak is clustered in the South Bronx. The Opera House Hotel there became the third location where cooling towers tested positive for the Legionnaires' bacteria, Kadushin said.

The other locations are a movie theater-mall complex, the Concourse Plaza; and a city-owned hospital, Lincoln Medical Center.

The infected towers have not been linked to actual illnesses, though epidemiological testing is pending, Kadushin said.

The hospital and hotel are open, but the theater, owned by National Amusements, is closed until further notice while the ventilation system is flushed and decontaminated, spokeswoman Nancy Sterling said. The shopping center has remained open, according to Bronx Borough President Ruben Diaz Jr.'s office.

Sterling said the infected system serves only the theater, not the rest of the shopping center.

Seventeen such cooling and water towers across the South Bronx have been tested so far.

The disease -- a type of treatable pneumonia so named because it was discovered after an outbreak at an American Legion meeting in 1976 in Philadelphia-- is transmitted through air-conditioning, showers, baths, cooling towers or other water sources. It cannot be transmitted between people.

Symptoms include coughing, shortness of breath, high fever, muscle aches and headaches.

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