An outbreak of Legionnaires’ disease on the Upper East Side of New York City has now infected 18 people, with some patients requiring hospitalization and in critical condition, according to city health officials. The number of confirmed cases represents a nearly sevenfold increase since the first two diagnoses were announced on July 2.
Health Commissioner Dr. Alister Martin confirmed Monday that many of the 18 patients are currently hospitalized, and while one patient has been discharged, the situation is still considered early. The city’s Department of Health is actively testing cooling towers in the affected area, which encompasses ZIP codes 10028, 10128, and 10075, corresponding to the Yorkville and Carnegie Hill neighborhoods. Officials suspect a cooling tower is the source of the bacteria.
Legionnaires’ disease is a pneumonia-like illness caused by the Legionella bacteria, which can spread through contaminated water vapor. It is not contagious from person to person and can be treated with antibiotics. However, the disease can be fatal if not treated promptly, and individuals over 50, smokers, and those with compromised immune systems or chronic lung conditions are at higher risk.
City officials are advising New Yorkers residing or working in the affected ZIP codes to seek medical attention if they experience flu-like symptoms. The health department is urging anyone experiencing such symptoms to contact a healthcare provider.
Following past outbreaks, the city has implemented regulations requiring quarterly inspections of the approximately 5,000 cooling towers across New York City. After a 2014 outbreak in the Bronx resulted in 16 deaths, laws were passed mandating these inspections. A more recent outbreak in Harlem last year, which caused seven deaths and hospitalized over 90 people, led to strengthened regulations. Building owners are now required to test for Legionella bacteria every 31 days when a cooling tower is in active use. Additionally, $13 million has been allocated to expand the Department of Health's cooling tower inspector team to 54, with community engagement initiatives also being launched. State-level legislation proposed in September 2025 aims to require the Department of Environmental Conservation and public water operators to maintain minimum disinfectant levels in water tanks, moving beyond inspection-based monitoring.