A growing outbreak of Legionnaires’ disease, a severe bacterial pneumonia, has put residents of New York City’s Manhattan Upper East Side on high alert, prompting city health officials to roll out an aggressive containment response while drawing criticism from local political leaders over the pace of action. As of this week, 46 confirmed cases of the infection have been recorded, with the city tracing the source of the outbreak to contaminated water cooling towers on large buildings across the neighborhood.
For many local residents like Justine Kirby, the outbreak has already changed daily routines. Kirby now wears a fitted N95 protective mask for every outdoor walk through the normally quiet neighborhood and keeps all apartment windows closed to reduce exposure risk. “I know the overall risk for most people is low, but until all contaminated sites are cleaned and disinfected, there’s no real downside to taking these extra precautions,” Kirby explained in an interview.
Health department data shows 22 of the 46 infected patients have required hospital admission, with a portion of those patients admitted to intensive care units for severe respiratory symptoms. Legionnaires’ disease is caused by Legionella bacteria, which thrive in warm water environments. When bacteria are carried through the mist emitted by cooling towers, people can inhale the pathogens and develop pneumonia. For immunocompromised individuals and untreated cases, the infection can be fatal.
Dr. Wafaa El-Sadr, an epidemiology professor at Columbia University Mailman School of Public Health, noted that cooling towers on large commercial and residential buildings are the perfect breeding ground for the bacteria, explaining how the current outbreak has spread through the dense urban neighborhood. “Warming temperatures driven by climate change are expected to make these kinds of outbreaks more frequent and severe over time, even though Legionnaires’ has been a documented public health risk in New York and other major global cities for decades,” Dr. El-Sadr added.
City health officials have launched what they call an aggressive response to the cluster of cases. New York City Health Commissioner Alister Martin told a packed community town hall held at a local Upper East Side church this week that early detection of the outbreak was a critical advantage for containment teams. “We have identified 160 cooling towers across the affected region that need testing, and we are not waiting to take action,” Martin said, per remarks obtained by ABC News. The current policy requires any building with a positive Legionella test to immediately complete full cleaning and disinfection of its cooling tower, rather than delaying action for additional confirmatory testing. As of this week, multiple building owners have already finished the disinfection process, with more work ongoing.
Not all local leaders are satisfied with the city’s response, however. New York City Council Speaker Julie Menin raised sharp concerns at the town hall and in a formal letter to Commissioner Martin, saying she is “deeply concerned that the Department of Health and Mental Hygiene has still failed to require building owners to proactively disinfect all cooling towers in the area under investigation.”
While Kirby said she feels reassured by the city’s widespread testing efforts, she added that many residents who attended the town hall still have unanswered questions about how to best protect themselves from exposure. City guidance currently advises residents to monitor for flu-like symptoms associated with the disease and seek immediate medical care if symptoms develop, but the health department has not issued a formal recommendation for or against outdoor masking for local residents. When contacted by the BBC for comment on masking guidance, the department did not respond. Dr. El-Sadr, however, said that well-fitted masking and closed windows are sensible protective steps for residents living in the core of the outbreak zone, a point Kirby says the city could have communicated more clearly.
This outbreak is the latest in a series of Legionnaires’ events impacting major North American cities in recent years. In 2025, an outbreak in London, Ontario, recorded 105 cases and five deaths. Last August, a Legionnaires’ cluster in Harlem, upper Manhattan, infected 114 people and killed seven, with investigators tracing the source to cooling towers at Harlem Hospital and a nearby city public health laboratory site. Notably, the Upper East Side currently holds more than three times the number of cooling towers that were tested during the 2025 Harlem outbreak, according to city health department data.