Officials expressed confidence that the deadly outbreak of Legionnaires' disease believed to be the largest in New York City history has been contained.

Mayor Bill de Blasio and city Health Commissioner Dr. Mary T. Bassett said the number of newly reported infections is waning and the likely sources of the flare-up that has killed at least seven people in the South Bronx have been pinpointed.

"This is the largest outbreak of Legionnaires' disease that we are aware of in New York City," Bassett said at a news conference at Lincoln Medical Center, where many of the victims are being treated and where a contaminated cooling tower was identified and cleaned.

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As of , seven people -- some of them seniors and all in their 50s or older with pre-existing medical conditions -- have died and 86 people in all have been sickened as part of Legionnaires' infections clustered in the South Bronx, officials said.

The bacteria is a treatable, noncontagious form of pneumonia and is usually transmitted through water mist. It was found in the cooling towers of five nonresidential buildings in the area, officials said.

Bassett said "the medical and the scientific evidence" shows the outbreak was caused by one or more of the infected towers. The sites have been decontaminated with bleach and bio-cleaning substances.

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She cautioned that additional testing on the samples from the cooling towers must be conducted to confirm that the city's "disease detectives" have found the outbreak's origin point. The structures are usually associated with newer construction and central air conditioning. They are different from visible rooftop water tanks.

De Blasio, meanwhile, said his administration and the City Council will introduce legislation by week's end to help prevent future outbreaks by setting "new inspection standards for buildings with cooling and condensing units."

City officials will seek to create a registry of buildings with cooling towers and require owners to submit to inspections. Those who don't comply will be hit with financial penalties, he said.

Legionnaires' disease, which Bassett said affects about 200 to 300 people each year in New York City, is believed to have broken out in the South Bronx on July 10.

Officials emphasized that the city's water supply is safe and most residents aren't at risk, but they urged people in the affected area who are exhibiting flu-like symptoms such as fever, coughing and shortness of breath to seek care.

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City officials said they have closely consulted with the U.S. Centers for Disease Control and Prevention and will convene a panel of epidemiologists for more guidance.