Legionnaires' Outbreak in Upper East Side
At a town hall meeting held at an Upper East Side church this week, New York City Health Commissioner Alister Martin announced that the city had identified the Legionnaires' disease outbreak early.
For several days, Justine Kirby has been wearing an N95 mask whenever she leaves her home to walk in her typically quiet Upper East Side neighborhood. She has also kept her apartment windows closed amid a growing outbreak of Legionnaires' disease, which has reached 46 confirmed cases linked by the city to contaminated water cooling towers.
This cluster of Legionnaires' infections—a severe form of pneumonia caused by Legionella bacteria—has raised concerns among local residents. Many attended the town hall to ask questions of the New York City health department.
"There is quite a level of concern in the community," Kirby said. "I'm the sort of person who likes to say that the risk may be small, but until the [cleaning and disinfecting] is done, I don't see much downside in taking these extra measures."
As of Wednesday evening, health officials reported that 22 individuals who fell ill had been hospitalized, with some requiring intensive care.
Understanding Legionnaires' Disease and Its Source
Legionnaires' disease is caused by bacteria that thrive in warm water environments, producing flu-like symptoms that can be fatal without treatment, especially for immunocompromised individuals.
The current outbreak has been traced to cooling towers on large buildings, where Legionella bacteria multiply. Infection occurs when people inhale bacteria-laden mist emitted from these towers, explained Dr. Wafaa El-Sadr, professor of epidemiology at Columbia University Mailman School of Public Health.
City's Response and Testing Efforts
This week, New York City announced an "aggressive" plan to combat the outbreak, committing to test all water cooling towers in the affected area.
On Friday, Mayor Zohran Mamdani confirmed that officials had completed testing of all cooling towers in the vicinity.
Health Commissioner Alister Martin reported that Legionella bacteria were detected in 31 cooling towers, including 19 buildings that had already disinfected their towers, according to CBS News, the BBC's US partner. The remaining towers were expected to be disinfected by Saturday.
Cooling towers are components of large air conditioning or refrigeration systems that cool indoor spaces by removing heat from indoor air using water and releasing it as mist outdoors. These towers are often located atop buildings, as noted by the New York City health department.
Officials have mandated that buildings must fully clean and disinfect their cooling towers after a single positive test result, rather than waiting for additional confirmation. Several building owners have completed this process, while others have begun it, according to the health department.
Community Concerns and Official Statements
At the Upper East Side town hall, Commissioner Martin expressed optimism about the early identification of cases.
"What we have in front of us is 160 cooling towers across this region that we are looking at, and we are not waiting," he said, as reported by ABC News.
However, Julie Menin, Speaker of the New York City Council, expressed concern that insufficient action had been taken.
She voiced her worries at the town hall and wrote to Commissioner Martin stating she was "deeply concerned that the Department of Mental Health and Hygiene has still failed to require building owners to proactively disinfect all cooling towers in the area under investigation."
Kirby acknowledged feeling reassured by the health department's testing efforts but noted that many attendees at the town hall still had questions about effective personal protection measures. The city has advised residents to monitor for symptoms and seek medical care, including testing, if symptomatic.
"They could quite reasonably say, 'Because risk is low, we're not recommending everyone mask outside. However a good well-fitted mask will protect you,'" Kirby said. "I think they could've gotten into that."
The health department did not respond to the BBC's inquiry regarding mask recommendations for local residents. Dr. El-Sadr commented that masking and closing windows could be beneficial for those in the outbreak's epicenter.
Climate Change and Historical Context
Dr. El-Sadr also noted that rising temperatures due to climate change could exacerbate Legionnaires' outbreaks, although the disease has affected New York and other major cities worldwide for decades.
In 2025, London, Ontario, experienced 105 Legionnaires' cases and five deaths. Last August, Harlem in upper Manhattan reported 114 infections and seven deaths. The outbreaks were traced to cooling towers at Harlem Hospital and the nearby site of the city's new public health laboratory.
The Upper East Side contains a large number of cooling towers—more than three times the number tested during the 2025 Harlem outbreak, according to the New York City Department of Health and Mental Hygiene.
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