New York City health officials are investigating a Legionnaires’ disease outbreak on the Upper East Side that has infected up to 36 people. Mayor Zohran Mamdani announced the city will release the addresses of buildings with contaminated cooling towers to ensure public transparency during the ongoing search for the source.
Cooling Tower Contamination and the Search for the Source
The outbreak is concentrated across three Upper East Side ZIP codes: 10028, 10128, and 10075, covering neighborhoods including Carnegie Hill, Yorkville, and Lenox Hill. According to ABC7NY, the city has identified 36 confirmed cases, with 22 of those patients hospitalized. Other reports from Gothamist and amNewYork cite slightly lower figures of 28 total cases and 21 hospitalizations as of Wednesday morning. No deaths have been reported in this cluster.
Health officials believe the bacteria is spreading via contaminated mists from water-cooling towers. The NBC New York report notes that the active testing zone stretches from roughly East 74th Street to East 97th Street.
The Health Department is employing a multi-stage testing process to pinpoint the exact source:
- Initial PCR Screening: Rapid tests completed in 24 to 48 hours. These can return positive results even if the bacteria are no longer alive.
- Culture Analysis: A more detailed process taking about two weeks to identify live bacteria.
- Whole-Genome Sequencing: The final step to match the bacteria in a tower to the specific strain infecting patients.
Dr. Alister Martin, the city health commissioner, told attendees at a town hall that he expects dozens of towers to test positive during the first round of screening.
Mamdani’s Transparency Pledge and Building Compliance
Mayor Zohran Mamdani is implementing an “unprecedented step” by pledging to release the addresses of all buildings whose cooling towers test positive during the initial screening. This move follows criticism of the previous administration’s handling of a similar outbreak in Harlem last year, where officials were accused of being slow to identify contaminated buildings.
“When there’s a public health threat, New Yorkers deserve urgency and transparency from their government,”
Mayor Zohran Mamdani, via Gothamist
The city’s water ecologists are sampling 160 registered cooling towers within the affected ZIP codes. As of July 6, 139 of those towers had been tested. Building owners found to have contaminated towers are being ordered to drain, clean, and disinfect their systems.
When asked during a town hall what happens if a building owner refuses to comply, Corinne Schiff, the health department’s deputy commissioner for environmental health, stated, “We’ve never had that happen,” adding that “they always comply.” Dr. Martin emphasized the gravity of the situation, noting, “This is a matter of life and death.”
Public Health Risks and Symptom Recognition
Legionnaires’ disease is a severe form of pneumonia caused by inhaling Legionella bacteria. It is not transmitted from person to person. Health officials have clarified that the risk is external; residents can safely drink tap water, bathe, and use home air conditioning systems.
“It’s important to understand the risk here isn’t coming from inside the building, it is coming from outside the building in these ZIP codes,”
Dr. Darien Sutton, ABC News correspondent
Symptoms typically develop two to 14 days after exposure. According to the Health Department and Dr. Sutton, the signs include:
- Fever, chills, and cough
- Shortness of breath or difficulty breathing
- Muscle aches
- Gastrointestinal symptoms
While most healthy people may not get sick, about one in 10 people who contract the disease are at risk of dying, particularly smokers, the elderly, and those with underlying health issues.
Regulatory Gaps and the Harlem Precedent
The current crisis follows a deadly outbreak in Central Harlem during the summer of 2025 that killed seven people and infected over 100. In response to that event, the New York City Council passed a law mandating that buildings test, clean, and report their cooling tower status every 90 days. However, that law only went into effect in May.
The scale of the current investigation is significantly larger than the previous one. The Upper East Side has more than three times the number of cooling towers in the investigation zone compared to the Harlem cluster.
“Is the Health Department focusing on those buildings that were not compliant? Because obviously we’re deeply concerned that the source of this outbreak has not yet been identified,”
Julie Menin, City Council Speaker
The city began its investigation on July 2 after identifying two cases that suggested a community source of infection. Since then, the impacted zone has expanded, leading some residents to realize they may have been sick without knowing the cause. Matt Sheldon noted that his wife had experienced two to three weeks of coughing, a pattern he only recognized after the public health alerts.
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