A Legionnaires’ disease outbreak on Manhattan’s Upper East Side has grown to 36 confirmed cases, prompting an extensive search of building cooling towers as health experts examine how warmer and more humid conditions may increase the wider risk of the bacteria spreading.
As of late July 8, New York City health officials reported 36 cases connected to the cluster, including 22 people who had been hospitalized. No deaths had been recorded. The affected area includes Carnegie Hill and Yorkville, covering ZIP codes 10028, 10128 and 10075.
The investigation began July 2 after the Health Department identified two cases located close to one another. Officials moved before the normal threshold for declaring a community cluster had been reached and began testing cooling towers throughout the neighborhood.
Approximately 160 cooling towers are registered in the three affected ZIP codes, although not all are operating or located inside the precise investigation area. By July 6, teams had collected samples from 139 towers, with additional testing planned for the remaining active systems.
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Buildings whose towers produce positive initial PCR screening results are being ordered to drain, clean and disinfect the equipment immediately. The city is also releasing the addresses of buildings with positive preliminary tests rather than waiting up to two weeks for confirmatory cultures.
Investigators have not yet publicly identified the tower responsible for the illnesses. A preliminary positive result can show that Legionella genetic material is present, but additional laboratory work is needed to determine whether live bacteria from a tower match bacteria collected from patients.
Legionnaires’ disease is a serious form of pneumonia caused by Legionella bacteria. People generally become infected after inhaling small droplets or mist containing the bacteria. It is not normally transmitted from one person to another.
Common symptoms include fever, cough, headaches, muscle aches and shortness of breath. Confusion, nausea or diarrhea may also occur. Symptoms usually appear between two and 14 days after exposure, and the illness can be successfully treated with appropriate antibiotics, particularly when diagnosed early.
City officials have emphasized that the outbreak is not connected to the plumbing inside individual homes. Residents can continue drinking tap water, showering, cooking and using window or building air-conditioning systems. The cooling towers under investigation release mist outdoors and are separate from the systems that cool air inside apartments.
Most healthy people exposed to Legionella do not become ill. The greatest risks affect people age 50 or older, current or former smokers, people with chronic lung disease and those with weakened immune systems or certain underlying medical conditions.
The Centers for Disease Control and Prevention estimates that approximately one in 10 people who develop Legionnaires’ disease die from complications. The risk is higher when the infection is acquired in a hospital or other health care setting.
The Upper East Side outbreak has also renewed discussion about climate and urban infrastructure. Legionella grows most effectively in warm water, particularly inside large, complex or poorly maintained systems. Research has found that warmer temperatures and higher humidity contribute to the seasonal increase in Legionnaires’ cases during summer.
Nationally, reported cases have generally increased since the early 2000s, with higher rates recorded among older adults, Black Americans, men and residents of the Northeast and Midwest. Cases are also more common during summer and fall.
However, warmer weather alone does not prove that climate change caused this particular outbreak. Cooling-tower maintenance, water temperature, stagnant water, disinfectant levels and aging equipment can all influence bacterial growth. The source must be determined through testing rather than assumed from the timing of the outbreak.
The incident nevertheless shows how rising temperatures may place additional pressure on cities with thousands of large buildings and aging water systems. More frequent periods of intense heat could extend the conditions in which Legionella survives and multiplies, making routine maintenance and rapid public-health surveillance increasingly important.
Why It Matters
The outbreak affects residents, workers and visitors in one of Manhattan’s busiest neighborhoods. Delayed diagnosis can result in serious illness, particularly among older adults and people with existing health conditions.
It also highlights the responsibility of building owners to inspect and maintain cooling systems. Poor maintenance can expose people outside a building who may never know they passed near contaminated mist.
What Comes Next
Health officials will continue testing cooling towers and comparing environmental samples with clinical samples from patients. Confirmatory testing and genetic sequencing may take several weeks, and the precise source may not be identified immediately.
People who have lived, worked or visited the affected Upper East Side area since late June should contact a health care provider promptly if they develop fever, cough or difficulty breathing, especially if they belong to a higher-risk group.
New York health officials are investigating 36 Legionnaires’ disease cases on Manhattan’s Upper East Side.
So far 36 cases have been reported, 22 requiring hospitalization, and no deaths.https://t.co/gjQNP97oDo
— Gothamist (@Gothamist) July 9, 2026
