Health officials in New York City say a cluster of Legionnaires’ disease in Central Harlem has grown to 99 cases, including four deaths.

Four people have died as a result of a Legionnaires’ disease outbreak in Harlem that has sickened nearly 100 people, and officials revealed the cooling towers that tested positive for the bacteria that causes the illness — some of which are at properties owned by New York City,

In the five ZIP codes affected by the outbreak, the number of inspections fell more dramatically than in the rest of the city.

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.

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.