The Legionnaires' disease cluster in the South Bronx has grown to 21 confirmed cases, and the NYC Health Department has extended its outreach into ZIP codes 10455 and 10459 after identifying cases within a few blocks of the original investigation area. The department's cluster page, last updated Sept. 20 at 7:20 p.m., lists three people currently hospitalized, 14 discharged, two who did not need hospital care, and two deaths.
The expansion matters most for households just outside the original boundary. The investigation remains centered on parts of Melrose and Morrisania in ZIP codes 10451 and 10456, but anyone who lives or works in the area, or has visited since late August, is urged to contact a provider right away if flu-like symptoms such as fever, cough, or trouble breathing appear. "Legionnaires' disease is deadly but can be effectively treated if diagnosed early," the department says.
The count has climbed quickly. It stood at 14 on the evening of Sept. 17, when the department confirmed the second death, Insurance Journal reported, and had reached 19 when the outreach zone widened, according to FOX 5 New York. The source of the bacteria has not been identified.
New Cases Push the Investigation Beyond Its First Boundary
Ten buildings in the original zone have cooling towers that tested positive for Legionella in a PCR screening test, including 1 E. 161st St., the address of Yankee Stadium, and properties on East 149th Street, Melrose Avenue, Park Avenue, Teller Avenue, and Washington Avenue. The department says all 10 towers have been cleaned and disinfected.
A positive PCR test detects traces of living or dead bacteria. It does not show that a tower made anyone sick. The department is also running culture tests on every sampled tower. Those results take up to two weeks and will confirm which towers held live bacteria when the water was collected. Even a culture-positive tower may not be the source of a cluster.
MedicalDaily previously reported on the second death and the city's tower disinfection. Since then, the case count has risen by half, and the outreach map has grown. Officials have not said whether the newest patients live inside the added ZIP codes or near their edges.
For families in 10455 and 10459, the practical step is not avoiding the neighborhood or tap water. The department says the disease does not spread from person to person and cannot be caught by drinking water, cooking, or using air conditioning. The real concern is an illness that feels like the flu but is actually pneumonia, which needs testing and antibiotic treatment.
Risk is highest for people 50 and older, people who smoke or vape, those with chronic heart, lung, kidney, or liver disease or diabetes, and people with weakened immune systems. Symptoms include fever, chills, muscle aches, and cough, and some people develop headache, fatigue, loss of appetite, confusion, or diarrhea. People in higher-risk groups should seek care right away and tell the clinician they are worried about Legionnaires' disease.
Cost should not be a barrier. The department says New Yorkers can get help finding a provider regardless of immigration or insurance status by calling 311 or 844-NYC-4NYC. A virtual town hall for residents of all four ZIP codes is scheduled for Tuesday, Sept. 22, at 6 p.m.
A Longer Legionella Season Frames the Bronx Cluster
The Bronx cluster is the city's second of the summer. The Upper East Side cluster ended with 94 cases and 11 deaths, and the department says that source has been eliminated. A national analysis published Sept. 9 in PLOS Global Public Health offers context for why late-summer clusters keep appearing.
In that study, Dr. Xiang Han, a laboratory medicine specialist at the University of Texas MD Anderson Cancer Center, reported that age-adjusted U.S. legionellosis rates rose from 0.40 to 2.37 cases per 100,000 people between 1999 and 2019, a 6.6-fold increase based on his statistical trend fit, with a peak of 2.69 in 2018. Rates fell to 1.67 in 2020 and rebounded to 2.21 in 2021. By 2018 and 2019, cases formed a seasonal plateau stretching from June through October.
Han linked the rise to decades of warming, rainfall surpluses, and vehicle miles driven, and he argues that spray from wet roads may carry soil bacteria to drivers. Natalie Exum, PhD, a Johns Hopkins environmental health researcher who was not involved, told CIDRAP News she doubts road spray is a primary source but sees a clear climate connection. "July, August, September is really when we're getting in the height of Legionella season," she said.
The evidence has firm limits. This is an ecological study that compares national and state trends, not individual patients, so it shows associations rather than proof of cause. It was written by a single author with no specific funding, its data end in 2021, and it cannot explain any particular New York cluster, which investigators tie to cooling towers. An aging population also plays a role, since adults 65 and older made up 44.9% of cases in 2021. Current prevention guidance has not changed.
What comes next depends on culture results due within the two-week testing window and on whether new cases keep appearing after disinfection. MedicalDaily previously covered the study's heat, rain, and traffic findings in more detail. For now, the most useful action is early testing for anyone at higher risk who develops fever and cough in or near the affected ZIP codes, a step that can turn a dangerous pneumonia into a treatable one.
Developing Story Timeline
Sept. 20, 2026, 7:20 p.m.: The NYC Health Department lists 21 cases and two deaths, with outreach now covering ZIP codes 10455 and 10459.
Sept. 17, 2026: The department confirms a second death, with 14 cases reported at the time.
Sept. 12, 2026: Ten cooling towers test positive for Legionella in initial PCR screening.
Sept. 10, 2026: The department announces it is investigating a community cluster in parts of Melrose and Morrisania.
Key Questions Answered
How many people are sick in the South Bronx cluster?
As of Sept. 20, the NYC Health Department reports 21 confirmed cases: three currently hospitalized, 14 discharged, two who were not hospitalized, and two deaths.
Which ZIP codes are affected?
The investigation centers on 10451 and 10456 in parts of Melrose and Morrisania. Outreach now also covers 10455 and 10459 because cases were found within a few blocks of 10456.
Has the source been found?
No. Ten cooling towers screened positive by PCR and were cleaned and disinfected. Culture tests, which take up to two weeks, will show which towers had live bacteria.
Can I get Legionnaires' disease from tap water, air conditioning, or another person?
No. The department says the disease is not contagious and is not spread by drinking water, cooking, or using air conditioning.
Who should seek care, and what are the symptoms?
Anyone in the four ZIP codes with fever, chills, muscle aches, or cough should contact a provider, especially people 50 and older, smokers, and those with chronic illness or weakened immunity. Help finding care is available through 311.
Does the new climate study explain this cluster?
No. The study links long-term national trends to warming, rainfall, and driving, but its data end in 2021, and it does not examine individual outbreaks.
