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

The disease is a form of pneumonia caused by water contaminated with Legionella, which can be found in cooling towers, showers and hot tubs.

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.