On Wednesday afternoon, Mayor Bill de Blasio, the city health commissioner and several elected leaders visited the Morris Park Association, a senior center, to discuss the flurry of cases and urge residents to visit a doctor if they notice any flulike symptoms. The latest cluster was “different than what we experienced a couple of weeks back in the South Bronx,” Mr. de Blasio said. “This is a much more limited situation.”

He said it was a good sign that all 13 who were sickened had started experiencing symptoms by Sept. 21, and that there was no uptick in emergency room visits for pneumonia. Health officials have not said when the single death occurred.

Inspectors took samples from 35 cooling towers in the Morris Park area over the weekend, and 15 of them tested positive for Legionella. Among those were towers at Lehman High School, the Bronx Psychiatric Center, and six buildings associated with the Albert Einstein College of Medicine. The commissioner of the Department of Health and Mental Hygiene, Dr. Mary T. Bassett, ordered those buildings “to begin cleaning and disinfection immediately,” the health department said in a statement on Wednesday.

Some of the patients live in Morris Park and others work there; all of them are middle-aged.

The city planned to hold a town-hall-style meeting on Thursday evening to answer residents’ questions, as the city health department continues to interview patients and try to home in on the source of the cluster. City officials consulted with the Centers for Disease Control and Prevention on Monday, and also notified the state health commissioner on Saturday.

Every year, there are about 200 to 300 cases of Legionnaires’ disease in New York City, though clusters like the one in Morris Park are considered more rare.