A man housed at New York City's Rikers Island jail has been diagnosed with Legionnaires' disease. Health officials, however, believe the latest case is not tied to the outbreak in the South Bronx outbreak that has killed 12 people.

Authorities announced Tuesday that a 63-year-old man locked up at the jail complex tested positive for Legionnaires' disease and is being treated at the jail ward of Bellevue Hospital Center. According to DNAinfo, he has been incarcerated at Rikers since December 2014, but he left on two different occasions to appear in a Brooklyn court.

The disease, which is a severe form of pneumonia, is caused by breathing in mist that comes from a water source, like cooling towers, air conditioning or showers. However, the water-borne illness cannot be transmitted from person to person.

The symptoms include headache, fatigue, appetite loss, fever, chills, confusion and diarrhea. Symptoms typically start to appear between two to 10 days after one experiences significant exposure to the bacteria.

Although authorities do not know where the man contracted the disease, all six cooling towers at Rikers Island were chemically disinfected out of caution, even though they were disinfected in July. The New York City Department of Corrections (DOC) announced that the showerheads were also cleaned.

Officials added that it was unlikely that the case was connected to the outbreak that has infected at least 115 people since it began in the South Bronx early last month.

Health officials say that five of 17 cooling towers inspected for legionella bacteria in the South Bronx tested positive. The five towers were at Streamline Plastic Co., Lincoln Hospital, the Concourse Plaza shopping center near Yankee Stadium, the Opera House Hotel and a Verizon office building. Since then, all five have been decontaminated.

In a statement, Bronx Borough President Rubén Díaz, Jr. said that he and New York City Councilmember Vanessa Gibson have proposed legislation "to ensure that we are proactive against the further spread of the Legionnaires Disease." Díaz also praised Mayor Bill de Blasio's "push for testing buildings throughout the city" as a positive step "in eliminating this problem while finding solutions to prevent yet another outbreak."