Twelve people have died from Legionnaires' disease in New York City, city officials announced Monday.

The death toll has risen up from 10 this weekend. The total number of cases reported since July 10 has climbed up to 113, up from 97. City officials also announced that "two more sites have tested positive for the bacteria that causes the disease," The Wall Street Journal reported. This brings the total number of sites to 12.

Legionnaires' disease is a respiratory bacterial infection that is caused by the bacteria Legionella. Most cases of Legionnaires' disease can be traced to plumbing systems where conditions are favorable for Legionella growth, such as hot tubs, humidifiers, hot water tanks, cooling towers, and evaporative condensers of large air-conditioning systems.

City officials believe that the outbreak was caused by one of the first five buildings that tested positive for traces of the legionella bacteria: Lincoln Medical Center, the Concourse Plaza shopping center, Opera House Hotel, a Verizon building and Streamline Plastics Co.

"We are taking this very seriously," Health Commissioner Dr. Mary Bassett told concerned Bronx residents at a public town hall meeting last week, the Associated Press reported.

According to the U.S. Centers for Disease Control and Prevention, most people who contract Legionnaires' disease recover. However, between 5 to 30 percent of people die. The seven victims were older adults with weakened immune systems due to additional underlying medical problems, a demographic that were at high risk of the flu-like disease.

"As we continue to investigate the potential sources of this cluster, we remind New Yorkers that this is a very treatable disease and we urge anyone who might be experiencing symptoms of Legionnaires' disease to seek medical attention immediately," Bassett said last month.

New Yorkers with respiratory symptoms, such as fever, cough, chills and muscle aches, are advised to promptly seek medical attention. Symptoms of the disease also include headache, fatigue, loss of appetite, confusion and diarrhea.