All of the people infected with the disease came down with it before Sept. 21, and all of them have underlying health issues, the city said.
Nine patients remain hospitalized, and three have been released, according to city officials.
The city tested 35 cooling towers over the weekend, 15 of which came back with positive results.
The infected buildings are:
► Chase Bank at 2725 E. Tremont Ave.
► Calvary Hospital at 1740 Eastchester Rd.
► Lehman High School at 2964 E. Tremont Ave.
► Bronx State Psychiatric at 1500 Waters Pl.
► Einstein College at 1199 Sackett Ave., 1845 Eastchester Rd., 1301 Morris Park Ave., 1250 Morris Park Ave., 1865 Eastchester Rd., and 1925-1935 Eastchester Rd.
The Health Department ordered all 15 infected sites to immediately begin the cleaning and disinfection process and said there has been no increase in the amount of emergency room visits for pneumonia.
The towers had been cleaned after the outbreak in the South Bronx from this summer, according to the Health Department.
Travis Book, an environmental group manager at Barclay Water Management, said it is fairly common for cooling towers to become reinfected with Legionella, the bacteria that causes Legionnaires' disease, even after being cleaned for it, given how ubiquitous it is.
"The Legionella bacteria is everywhere. It’s all over the place," he said.
This is not necessarily a sign that the towers were cleaned improperly the last time around but rather just an indication of how widespread Legionella is, Book added.
"If you washed your car super, super well and then left it out, it’s going to get dirty again. It’s just going to happen," he said. "It’s kind of the same idea."
Officials said that this cluster is unrelated to the summer outbreak, which killed 12 people and sickened more than 120.
Legislation passed in the wake of that outbreak requires building owners to register their cooling towers with the city, and City Council Speaker Melissa Mark-Viverito said members would now see if there are any additional steps they can take to help guard against future cases of Legionnaires’ disease.
"We've implemented legislation to ensure ongoing cleaning of the towers,” she said, “and we'll look at other alternatives as well.”
Mayor Bill de Blasio repeatedly described the City Council's legislation as the "strongest in the country" during a Wednesday visit with the Morris Park Association, a senior center in the impacted neighborhood. He called the current outbreak a much more "limited" situation than the outbreak in the South Bronx.
"We went through a painful episode but we learned a lot from it. We acted and it's allowing us this time to react very quickly and make sure that we can contain the problem and keep people healthy," said de Blasio.
Some seniors at the event expressed concerns about the safety of going to the hospital since the bacteria was discovered in the cooling towers of two hospitals.
"Anyone who stayed away from the hospital would be putting their own life in danger," said the mayor who explained that Lincoln Hospital's cooling towers had tested positive for legionella but no one caught the disease there.
The South Bronx hospital treated dozens of patients who had contracted Legionnaires'.
"The danger is not getting medical attention. That is the singular danger," said de Blasio.
There is a town hall meeting about the disease scheduled for 8 p.m. on Oct. 1 at 1703 Bronxdale Ave.