New York City health officials are racing to trace the source of a new Legionnaires' disease cluster in the South Bronx after confirming five cases and one death in the neighborhoods of Melrose and Morrisania over the past week.

The NYC Health Department said the cluster is concentrated in ZIP codes 10451 and 10456, and that additional suspected cases are still pending lab confirmation. Anyone who has lived, worked, or spent time in the affected blocks since late August and is experiencing flu-like symptoms — fever, cough, chills, muscle aches, or shortness of breath — is being urged to see a doctor immediately.

Legionnaires' disease is a severe form of pneumonia caused by inhaling water droplets contaminated with Legionella bacteria, which typically breeds in warm, standing water such as building cooling towers, decorative fountains, and hot tubs. It is not spread person to person. Older adults, smokers, and people with weakened immune systems or chronic lung conditions face the highest risk of serious illness.

Cooling towers under the microscope

Environmental health crews have already collected water samples from cooling towers throughout the two ZIP codes and sent them to the city's Public Health Laboratory for testing, according to NBC New York. Any tower that tests positive for the bacteria will be ordered to undergo immediate cleaning and disinfection, a process the city has used to shut down prior clusters.

Health Commissioner Dr. Alister F. Martin confirmed the toll in a statement carried by NBC New York: "Our disease investigators have confirmed five cases... Sadly, one person has died."

"WE SAW WHAT HAPPENED IN HARLEM AND THE UPPER EAST SIDE, AND WE KNOW THAT BEING PROACTIVE IS THE BEST WAY TO STOP FURTHER SPREAD."

That warning, from Assemblyman Landon Dais, referenced two earlier Legionnaires' clusters that hit New York City this year — including a Manhattan outbreak this summer. Officials say the Bronx cluster is the city's second major community cluster of 2026, and public health workers are set to begin canvassing Melrose and Morrisania door to door, distributing multilingual flyers about symptoms and prevention, per local reporting.

The Health Department has also scheduled a virtual town hall for area residents this Sunday, September 13, to answer questions about testing results, exposure risk, and next steps as the investigation continues. City officials stressed that tap water remains safe to drink and shower in — the concern is limited to aerosolized mist from cooling systems, not the drinking water supply.

Bronx Borough President Vanessa L. Gibson was among the officials who first disclosed the cluster, and local lawmakers have pressed the city to move quickly on inspections after Melrose apartment complexes were previously flagged in past Legionnaires' scares. The Health Department has not yet identified a confirmed source tower and says the investigation remains active.

City health officials say they will update the public as more test results come back and stressed that most healthy people exposed to the bacteria do not become seriously ill.