Live Legionella bacteria were confirmed in 59 of the 183 cooling towers New York City tested during this summer's Upper East Side Legionnaires' disease cluster, according to data published by the New York City Health Department. That is close to one in three of every tower sampled, and it is the number that best describes the scale of a problem sitting on rooftops across the city.
The cluster itself has ended. The city recorded 92 diagnosed cases and seven deaths, with no cases diagnosed after July 21, and said it is confident the source of the bacteria has been eliminated. Those counts were last updated on July 30 and will not be revised further.
For households in Carnegie Hill, Yorkville and any dense neighborhood with rooftop cooling equipment, the relevant point is not the case count. It is that a routine piece of building machinery, invisible from the sidewalk, produced a fatal pneumonia cluster in back-to-back summers.
The Numbers Behind the Rooftop Problem
The city sampled 183 cooling towers at 160 buildings. Initial polymerase chain reaction screening flagged 77 towers at 75 buildings. Confirmatory culture testing, which shows whether bacteria are alive rather than simply present as genetic material, came back positive for 59 towers at 58 buildings. All of those were cleaned and disinfected. A total of 124 towers tested culture-negative.
The health department has been explicit that a culture-positive tower may or may not have been the source of exposure, and no single tower has been publicly identified as the origin. The distinction between the two tests matters for anyone reading building lists. Screening detects genetic material from bacteria that may be living or dead. Culture confirms live organisms capable of causing illness.
This was the second consecutive summer with a deadly cluster. A Central Harlem outbreak ended on August 29, 2025 after 118 cases, 92 hospitalizations and seven deaths. Taken together, the two clusters account for 14 deaths across 2025 and 2026.
Regulation Arriving After the Deaths Rather Than Before
New York City has regulated cooling towers since 2015, when a South Bronx outbreak produced 138 cases and 16 deaths, the largest Legionnaires' outbreak in city history. Owners must register their towers, maintain them to health code standards, and submit Legionella test samples on a schedule.
Following the Harlem cluster, the City Council tripled the required testing frequency from every 90 days to every 31 days while towers are operating. The health department announced the new regulations as summer approached, hired 23 new water ecologists, and received an additional $13 million in the fiscal year 2027 budget for routine inspections and cluster response.
Compliance did not immediately follow. A review of health department records by The City Reporter during the investigation found more than 500 Manhattan cooling towers out of compliance with the monthly sampling requirement. Council Speaker Julie Menin wrote to Health Commissioner Alister Martin during the cluster, asking the agency to order all towers in the three affected ZIP codes drained and disinfected as a precaution.
In August, Governor Kathy Hochul signed legislation requiring owners and operators of New York City cooling towers to certify twice a year that towers have been inspected, tested, cleaned and disinfected in compliance with the city administrative code. Owners must notify the Department of Buildings within 24 hours and correct maintenance deficiencies within 48 hours when testing detects dangerous microbe levels. Civil penalties rise to $2,500 for a first violation, $7,000 for later ones, and up to $12,500 when a violation results in serious injury or death.
Who Actually Gets Sick from a Rooftop
Legionnaires' disease is a form of pneumonia caused by bacteria that grow in warm water. People get sick by breathing in mist containing the bacteria, most often from cooling towers, hot tubs or decorative fountains. It is not contagious between people, and it cannot be caught by drinking water, cooking, or running an air conditioner.
Most people exposed do not develop the illness. The health department identifies higher risk in people aged 50 and older, people who smoke or vape, people with chronic heart, lung, kidney or liver disease or diabetes, and people with weakened immune systems from a condition or a medication. That profile is why a cluster in a residential neighborhood with many older adults produced deaths while most exposed residents never fell ill.
Symptoms include fever, chills, muscle aches and cough, and can also include headache, fatigue, loss of appetite, confusion or diarrhea. There is no vaccine, but the illness is treatable with antibiotics, and most people recover with early treatment.
Reasonable Steps for Renters, Owners and Boards
Residents can look up inspection results for cooling tower systems by building address or building identification number through the health department. That is a more useful step than avoiding a neighborhood, because the exposure route is airborne mist near a tower rather than anything a household controls indoors.
Anyone in a higher-risk group who develops fever with cough or shortness of breath should seek medical attention promptly and tell the clinician they are concerned about Legionnaires' disease, since the test is not part of a routine pneumonia workup unless it is requested. Severe breathing difficulty, chest pain, or confusion warrants urgent evaluation.
Building owners and co-op boards carry the operational burden. Under current rules, that means monthly sampling during operation, timely submission of results, prompt notification when a hazard is found, and the new twice-yearly certification. Buildings without a documented water management plan are the ones most likely to be caught out.
What remains unresolved is whether compliance improves under the new certification regime, whether inspector staffing keeps pace, and the outcome of a threatened lawsuit by roughly 50 Harlem residents over last summer's outbreak.
Key Questions Answered
How many cooling towers tested positive? New York City tested 183 cooling towers at 160 buildings. Live Legionella was confirmed by culture in 59 towers at 58 buildings, and 124 towers tested culture-negative. All culture-positive towers were cleaned and disinfected.
Is the outbreak still active? No. The health department reported no cases diagnosed after July 21 and said it is confident the source has been eliminated. Case counts were last updated on July 30 and are no longer being revised.
How many people were affected? The Upper East Side cluster produced 92 diagnosed cases and seven deaths. A Central Harlem cluster that ended in August 2025 produced 118 cases, 92 hospitalizations, and seven deaths.
Can Legionnaires' disease spread from person to person? No. It is not contagious. People get sick by inhaling mist containing the bacteria. It cannot be caught by drinking water, cooking, or using an air conditioner.
Who faces the highest risk? People aged 50 and older, people who smoke or vape, people with chronic heart, lung, kidney, or liver disease or diabetes, and people with weakened immune systems.
What has changed in the law? Testing frequency went from every 90 days to every 31 days during operation. New state legislation signed in August requires twice-yearly certification, sets 24-hour and 48-hour deadlines for notification and correction, and raises civil penalties.
