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

Rainwater left untreated in cooling towers atop city-owned Harlem Hospital fueled the Big Apple’s deadliest Legionnaire’s disease outbreak in a decade, the Rev. Al Sharpton charged Tuesday.

A law firm filed a lawsuit Aug. 20 against a New York City hospital’s construction company, alleging the company failed to treat bacteria-infected water in its cooling towers, leading to a Legionnaires’ disease outbreak.

Two construction workers who claim they contracted Legionnaires' disease while working at or near Harlem Hospital Center are suing contractors they allege failed to safeguard water cooling towers at the building against contamination by the bacteria that causes the illness.

A Legionnaires' outbreak in Harlem has prompted concerns about NYC's health oversight after a decline in cooling tower inspectors, despite funding increases. Former Governor Cuomo seeks an independent probe into the city's handling of the crisis.