
The island and buildings now stand abandoned.
Disaster

The fire is believed to have started in the lamp room, quickly catching hold as it lit up the straw and lamp oil. A poorly extinguished and discarded cigarette or match being the likely suspect. The fire spread to other rooms aboard the Slocum, including the paint locker and gasoline stores.
The crew quickly scrambled to put out the blaze, but the safety equipment on the General Slocum was not up to scratch. Fire hoses had not been replaced in years, the rotted tubing falling apart in the crews hands. The lifeboats that could have allowed passengers to depart to safety were attached to the hull with wire and had been painted over, making them all inaccessible. Life jackets were old, the canvas filled with holes allowing the cork, the buoyancy, to escape... what's more is that iron bars had been placed in the bottom of the jackets to ensure they kept people floating upright... in this case all it did was cause people to sink faster.

In the end, the General Slocum sank in shallow water just off North Brother Island. More than 1000 people drowned or burned alive. The date was June 5th, 1904, and it was the worst disaster in New York City, in terms of loss of life, until September 11, 2001.
Many of the victims washed ashore on the banks of North Brother Island which, at that point in time, was a quarantine hospital for contagious and deadly diseases.

Since 1885 the island had been home to the Riverside Hospital, a smallpox hospital that later treated other quarantinable diseases.
Three years after the General Slocum disaster, the hospital would receive a patient that would cause more media attention to be centred on the island.
Mary Mallon was a career cook, but for many she worked for she would present them with something else asides from food... she would also give them a sickness, one that would prove deadly for some.
Mary

It is not sure how many people Mallon infected with the disease, but estimates run as high as the hundreds, with possibly as many as fifty deaths. The disease was rampant, and when the media found out about Mary Mallon, how she was a carrier who did not get sick herself, she simply spread the disease wherever she went, they gave her a nickname.
The disease was Typhoid.
She was known as Typhoid Mary.
Mary was quarantined for three years on North Brother Island, but then it was decided that asymptomatic carriers should not be kept in isolation. Mary was released as long as she no longer worked as a cook. She agreed to this but sometime after release she changed her name and went back to work as a cook, further infecting people and causing more fatalities.

After Mary's death in 1938, the hospital ran for a few more years before it was closed and the island abandoned. It was later reused as accommodation for college students after World War II, then in the 1950's it was used as a detox and rehabilitation centre for adolescent drug addicts. This centre closed due to staff corruption, and what was considered cruel treatment of addicts.
Abandoned

Photos from these visits reveal that the hospital seemed to be abandoned with quite some haste – furniture still adorns the rooms, beds (some still with sheets and blankets) can be found in patients rooms, even some of the sets of keys, used by staff to access the rooms, can be found on shelves and in desks.

The paint peels, the ceilings sag and the boilers rust. One can only imagine what the walls whisper.
As far as my searches tell me, there are no reported hauntings on North Brother Island, but then no one has been there long enough to have such experiences.