The death toll from the latest outbreak of Legionnaires’ disease in New York City has risen to 12, Mayor Bill de Blasio said in a briefing Monday. The total number of people suffering from the disease in the South Bronx, where the current outbreak began, has reached 114 since July 10, NBC New York reported Monday.

Officials said that the latest victims of Legionnaires’ disease, a severe form of pneumonia, were middle-aged people with underlying health issues. De Blasio said that the cases added to Monday's total were not new ones but those that were not reported before, adding that it was a "very promising sign" that no new cases were reported since Aug. 3. State and city health officials said, according to the Associated Press, that 18 buildings have so far tested positive for the Legionella bacteria, which causes the disease.

"We are confident the Legionnaires' outbreak in the South Bronx has been contained, and are working with our partners in the City Council to protect the entire city in the long-term through stringent new regulations for building owners," de Blasio said, according to ABC News, adding: "New York is the first major city in the nation to propose new registration, inspection, and enforcement standards for the cooling towers which harbor Legionnaires' bacteria."

Gov. Andrew Cuomo said, according to ABC News, that over 500 building sites in the Bronx were canvassed in two days to identify cooling towers that could be a potential source of Legionella, which breeds in warm water in places like hot tubs, hot water tanks, large plumbing systems and decorative fountains. Samples from cooling sites will be taken by teams led by the New York State Office of Emergency Management and the Office of Fire Prevention and Control to determine the sites that may be containing the bacteria.

"We are taking every precaution to prevent the spread of Legionnaires' Disease," Cuomo said, according to ABC News, adding: "This outbreak has been a source of great concern for people throughout the Bronx and the rest of New York City, but residents should know that we are doing everything necessary to protect the public health."

The bacteria spreads through mist or vapor and symptoms for the disease include cough, shortness of breath, high fever, muscle aches and headaches. The symptoms begin showing within two to 14 days of exposure and can be treated with antibiotics.