Four people in New York City's Harlem neighbourhood have died from an outbreak of Legionnaires' disease, an aggressive and potentially deadly form of pneumonia. The city has seen 99 confirmed cases with 17 people in hospital with the infection, according to the New York City Department of Health.

The Legionnaires' disease outbreak in Central Harlem has been traced to 12 cooling towers, including several at city-run buildings, officials said.

The health department offered five ZIP codes in central Harlem -- 10027, 10030, 10035, 10037, 10039 – that were at the center of the cluster, as officials stressed the disease was airborne and could reach people even outside of the directly affected buildings.