By Katie Reilly

NEW YORK (Reuters) - Mayor Bill de Blasio said on Tuesday a historic outbreak of Legionnaires' disease that killed seven New Yorkers has triggered an effort to mandate city-wide inspections and cleanings of air conditioning cooling towers.

Since July 10, the disease has sickened 86 people in the South Bronx, a New York City neighborhood that is one of the poorest in the United States, the mayor said at a news conference with Mary Bassett, the city's health commissioner.

The number could climb higher since the last disinfection of cooling towers tied to the outbreak took place on Monday, and the incubation period for Legionnaires' disease is 10 days. But officials said the outbreak has peaked, and they've seen a reduction in the rate of its growth.

The disease, a severe kind of pneumonia, is contracted by breathing in mist from cooling towers infected with the bacteria Legionella.

Of the 17 cooling towers that city health officials have inspected for Legionella, five tested positive. Remediation was completed at each of the locations, all in the South Bronx.

De Blasio said he would propose legislation this week to prevent future outbreaks, including regular cooling tower inspections, new recommendations for an immediate outbreak response and sanctions for failing to comply with new standards.

"For too long, the risk of Legionnaires' was underestimated. We are going to be very aggressive in dealing with this problem," de Blasio said.

De Blasio said he is confident the city has identified the only sites that caused the outbreak, though he acknowledged the lack of a complete registry of the city's cooling towers, which is something he said the new legislation will correct.

New York's drinking water supply has not been affected by Legionella, according to city health officials.

All the people who died of the disease were all older adults with underlying medical problems.

"People with underlying illnesses, including chronic lung disease, which can be asthma, can be emphysema, or chronic bronchitis, are people who are more at risk, so there is a higher underlying disease burden in the South Bronx," health commissioner Bassett said.

The city's last Legionnaires' outbreak was also in the Bronx, where 12 people fell ill in December 2014.

Legionnaires' disease is most common in the summer and early fall, according to the U.S. Centers for Disease Control and Prevention. Symptoms include fever, cough, headaches and muscle aches.

(Reporting by Katie Reilly; Editing by Doina Chiacu)