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.

About one in 10 people who get sick from Legionnaires' disease die from the disease due to complications from illness, CDC said.