A Legionnaires' disease cluster in the Harlem area of New York City has caused five deaths and sickened over 100 people. Here's what it is, symptoms and how it's spread.

A 2015 outbreak of Legionnaires' disease, traced to a cooling tower at a hotel, forced New York City to address a problem that had long been suspected but never adequately addressed: the role of buildings in spreading Legionella bacteria through the air.

G overnor Kathy Hochul defended New York City's response to the Legionnaires ' disease outbreak after officials on Tuesday confirmed the death toll had risen to five.