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

NEW YORK -- A fourth person has died in connection with a Legionnaires’ disease outbreak in New York City, health officials disclosed Thursday as they revealed that some cooling towers that tested positive for the bacteria are in city-run buildings.

A fourth person has died amid the Legionnaires’ disease outbreak in central Harlem, according to the New York City Department of Health. The outbreak that began in late July has since spread to 99 confirmed cases as of Thursday, with four deaths and 17 hospitalizations. Those who have died have not been identified.