South Bronx Legionnaires' Cluster Grows to 23 Cases as Source Remains Unconfirmed

A cluster of Legionnaires' disease in the South Bronx has grown to 23 confirmed cases and two deaths, New York City health officials said this week, as investigators continue to search for the source of an outbreak that has persisted for nearly three weeks despite the disinfection of every cooling tower found to carry the bacteria.

The New York City Health Department first announced the community cluster on September 10, identifying five cases and one death in the Melrose and Morrisania sections of the South Bronx. The case count has climbed steadily since, even as the department ordered the cleaning of ten rooftop cooling towers and expanded its outreach into two additional ZIP codes.

A second Bronx cluster in a single year

The outbreak marks the second Legionnaires' cluster to strike New York City in 2026. An earlier one, centered on the Upper East Side's Carnegie Hill and Yorkville neighborhoods, sickened 94 people and killed 11 before it was declared over in late July. That two clusters of this scale have emerged in the same city within a few months is unusual even by New York's own recent history with the disease, and it has renewed scrutiny of how the city's water systems are inspected and maintained.

Legionnaires' disease is a severe form of pneumonia caused by Legionella bacteria, which grow in warm, stagnant water and spread when that water is aerosolized, most often by rooftop cooling towers that serve large buildings' air-conditioning systems. According to the Centers for Disease Control and Prevention, the disease is not spread person to person, symptoms typically appear two to fourteen days after exposure, and roughly one in ten people who become infected die of the illness, a share that rises to about one in four among patients who are already hospitalized for other reasons when they are infected.

The numbers behind the investigation

City health officials have released a running tally of the cluster's progression since the investigation opened:

• September 10: five confirmed cases, one death, in ZIP codes 10451 and 10456
• September 13: nine cases, one death, three hospitalized; ten cooling towers ordered cleaned by September 14
• September 15: outreach town hall draws residents' complaints as the count reaches 14 cases and two deaths
• September 23: 22 cases, two deaths, three hospitalized, 15 discharged; seven of ten towers confirmed to hold live bacteria
• Late September: case count rises to 23, with two deaths and three people still hospitalized

Of the ten cooling towers that initially tested positive by PCR screening for Legionella DNA, the department reported in a September 23 update on the preliminary tower list that culture testing, which detects live rather than residual bacteria, confirmed seven of them as positive: addresses at 567 Melrose Avenue, 3339 Park Avenue, 820 Concourse Village West, 470 East 161st Street, 890 Washington Avenue, 1160 Teller Avenue and 1265 Franklin Avenue. All seven were disinfected, in most cases more than a week before the culture results came back, and none has been formally linked to any of the 23 illnesses. Two of those addresses, 820 Concourse Village West and 1265 Franklin Avenue, were also cited in an earlier department notice for failing to submit required testing records on schedule.

Yankee Stadium, whose cooling equipment returned a preliminary positive on PCR screening, has not been confirmed as a source. The team said in a statement carried by the local NBC affiliate that no current cases had been associated with the stadium and that the health department had not asked it to postpone games.

How the city's defenses were built, and why they did not stop this cluster

New York City's regulation of cooling towers dates to a 2015 outbreak in the South Bronx that killed 16 people and sickened more than 130, at the time the deadliest cluster in the city's history. That outbreak produced Local Law 77, the first law of its kind in the country, which required all cooling towers, condensers and fluid coolers to be registered with the city and tested regularly for Legionella. The rules were tightened again after a 2025 cluster in Central Harlem sickened well over 100 people, and as of building owner requirements the department updated this year, operators must now sample for the bacteria at least once every 31 days and report results to the city's registration portal within five days of collection. Roughly 5,000 cooling tower systems are currently registered in the city.

That a cluster of this scale emerged anyway, in the same stretch of the South Bronx where the 2015 outbreak began, has become a point of contention at community meetings. Health officials note that testing catches contamination after it occurs rather than preventing it outright, and that a positive test does not by itself prove a tower sickened anyone. Nationally, the CDC estimates that 5,000 to 8,500 Legionnaires' cases are diagnosed each year in the United States; New York City alone typically records 200 to 700 cases and about a dozen deaths annually, a baseline load that predates any of the recent clusters.

Who is affected

The outbreak is concentrated in ZIP codes 10451 and 10456, covering Melrose and Morrisania, with the health department's outreach since expanded into the adjoining 10455 and 10459 after cases turned up within blocks of the original cluster boundary. The department has said anyone who lives, works or has spent time in the area since late August should contact a doctor promptly if they develop fever, cough or shortness of breath. People over 50, smokers, and those with chronic lung disease or weakened immune systems face the highest risk of severe illness, consistent with CDC guidance on the disease generally.

State Senator José M. Serrano, whose district covers part of the affected area, told a September town hall that the neighborhood's underlying health profile compounds the danger.

"Communities like the ones I represent in the South Bronx face disproportionate negative health disparities that make our residents far more susceptible to severe disease if they contract Legionnaires'."

What officials and residents are saying

Health Commissioner Dr. Alister Martin has framed the response as methodical rather than reactive. Announcing the cluster on September 10, he said disease investigators had "confirmed five cases of Legionnaires' disease and are working quickly to identify and confirm any additional cases in the area." Two weeks later, as the case count neared its current level, he said the department was "moving decisively and deliberately to protect New Yorkers from this Legionnaires' disease cluster in the South Bronx," and told residents at a town hall that inspectors were rechecking every previously positive tower "independent of the last inspection" to see what conditions had allowed the bacteria to persist.

Some residents have said the briefings have not fully addressed their concerns. Bruce Burgos, an immunocompromised Melrose resident, told the Bronx Times that a September 15 town hall did not ease his fears about ongoing exposure. Fellow resident Julian DeJesus pressed officials for a longer-term fix, arguing that rising summer temperatures will keep straining the cooling systems that host the bacteria. Assemblymember Landon Dais said his office would keep canvassing the district to make sure residents "know the signs and symptoms of Legionnaires'."

What happens next

Culture results were still pending on several additional cooling towers as of this week, and the health department has not identified a definitive source for the outbreak, meaning further case counts, tower results or affected-area expansions remain possible in the days ahead. Officials have repeatedly said tap water remains safe to drink and shower in, and that air conditioners and public cooling centers are safe to use, since the risk comes specifically from inhaling mist generated by contaminated cooling towers rather than from drinking water or window units. The department has said it will continue independent rechecks of the seven confirmed towers and will update case figures as new diagnoses are confirmed.