A fourth person has died of Legionnaires' disease in an outbreak of the treatable disease clustered in the South Bronx that has now sickened 65 people, the mayor's office said Saturday.

Just a day earlier, the tally was three deaths and 46 infections since July 10, the date of suspected first case.

All of the fatalities have been of older adults with pre-existing health problems, like lung problems or compromised immune systems, said city spokesman Peter Kadushin.

The disease -- a type of treatable pneumonia -- is transmitted through air-conditioning, showers, baths, cooling towers or other water sources. It can't be transmitted directly between people.

The health department said it tracked the disease to five buildings which tested positive for Leginonnaires' in its cooling systems, Remediation was completed at four out of the five locations Saturday, according to the health department.

Symptoms include coughing, shortness of breath, high fever, muscle aches and headaches.