(CNN) — Health officials in New York City say a cluster of Legionnaires’ disease in Central Harlem has grown to 99 cases, including four deaths .

Health officials suspect the bacteria that causes the disease, Legionella, originated cooling towers — devices that uses water to cool large buildings and then disperse mist into the air. If the water inside becomes too warm, stagnant, or isn’t properly disinfected, Legionella can grow and sicken people who inhale the mist.

On Thursday , the New York City Department of Health confirmed positive tests of the bacteria in 12 cooling towers serving 10 buildings in the area, including NYC Health + Hospitals/Harlem .

The Department of Health says 11 of the 12 cooling towers have already been repaired and the final tower should be remediated b

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