Three people in central Harlem have already died from legionnaires’ disease, according to the NYC Health Department.

What are the symptoms of this type of pneumonia, called Legionnaires' disease, and how do you treat it? Here's what you need to know.

The health department offered five ZIP codes in central Harlem -- 10027, 10030, 10035, 10037, 10039 – that were at the center of the cluster, as officials stressed the disease was airborne and could reach people even outside of the directly affected buildings.