Legionnaires' disease is a respiratory bacterial infection usually spread through mist that comes from a water source, such as cooling towers, air conditioning or showers. It is not transmitted person to person. Symptoms of the disease include fever, chills and a cough.
An outbreak of the disease in the Bronx has claimed seven lives, de Blasio said. All of the victims were older adults with additional underlying medical problems.
Five additional cases were confirmed between Monday and Tuesday, de Blasio said, calling it a slowdown.
The outbreak has reached its peak, he said.
Five cooling towers have tested positive for Legionnaires' disease, and decontamination has commenced, including on the cooling tower on the top of Lincoln Hospital, de Blasio said.
The city believes it has identified all of the targets that have been contaminated, he said.
Most people recover, but between 5% to 30% of those who get the disease die, according to the U.S. Centers for Disease Control and Prevention. An estimated 8,000 to 18,000 hospitalized cases of Legionaires' disease occurs each year in the United States. An outbreak of the disease in Philadelphia in 1976, largely among people attending a convention of the American Legion, led to its name.
"We are conducting a swift investigation to determine the source of the outbreak and prevent future cases. I urge anyone with symptoms to seek medical attention right away," Dr. Mary Bassett, commissioner of New York City's health department, said last month.
The department's probe includes testing water from potential sources in the area.
De Blasio reiterated there is no risk to the city's water supply.
Bronx Borough President Ruben Diaz Jr. said on Friday that his office will push for legislation to create a citywide inspection system that would test building water infrastructure for the disease and others.
An outbreak of the disease killed two people
at a hotel in downtown Chicago in 2012.