The city said Friday that the spread of its worst known Legionnaires' disease outbreak in history appears to be slowing, but the state is "taking matters into our own hands," Gov. Andrew M. Cuomo said, and dispatching personnel to the South Bronx, the locus of infection.

City authorities identified only one new Legionnaires' diagnosis in the past few days and no new death -- a contrast with previous public updates that showed the flare-up worsening since the first case on July 10. The ebbing comes after nearly a month in which at least 10 died and 101 got sick, the health department said.

Yet within hours of each other, the state and city were issuing different messages.

"We're optimistic that we've seen the worst of this outbreak," the city's health commissioner, Dr. Mary Bassett, said in a statement.

Later in the afternoon, the governor called in on a NY1 news show to say that people in the South Bronx "have a good reason to be concerned."

"I understand the anxiety," Cuomo said. "It is almost like a bad science fiction movie."

The administrations of Cuomo and Mayor Bill de Blasio have sparred before over how best to handle a public-health emergency: in October, Cuomo ordered that health care workers who had been in Ebola-ravaged nations be quarantined, without telling de Blasio about the plans. Bassett appeared to chafe on Twitter at the idea.

All who died of Legionnaires' had pre-existing health conditions, such as weakened immune systems or lung infections. Cooling towers atop buildings are the suspected culprits spreading the disease. So far, at least five such towers have been found to contain the legionella bacteria and were decontaminated. Earlier this week, Bassett ordered that all towers citywide be tested and cleaned. But city officials admit they don't know definitively the number and location of all the towers.

Cuomo said the state would provide free testing for buildings with cooling towers or other equipment conducive to the bacteria.

Legionnaires' disease -- so named after the first identified cases at an American Legion convention in 1976 -- is a treatable bacterial pneumonia. It's caught through air conditioning, showers, baths, cooling towers and other water sources, and isn't contagious between people. Symptoms include coughing, shortness of breath, high fevers, muscle aches and headaches.