A Legionnaires' disease cluster in the Harlem area of New York City has caused three deaths and over 70 people to be sickened. Here's what it is, symptoms and how it's spread.

Three people have died and at least 67 people have been diagnosed with Legionnaires’ disease in a cluster that broke out in New York City last week.

As of Thursday evening, there had been three deaths, which was the same number as the day before. However, the city’s Health Department said there were now 81 confirmed cases, up from 73 the day before.