New York City officials say they believe the source of a Legionnaires’ disease cluster on the Upper East Side has been eliminated, even as the death toll connected to the outbreak has risen to four.
The city has identified 76 cases as of Monday, according to the Health Department. Seven patients remain hospitalized, while 53 people who had been admitted for treatment have since been discharged.
Officials have linked the illnesses to Legionella bacteria detected in cooling towers at buildings in the area. Cooling towers at 76 properties tested positive for the bacteria, prompting the city to order building owners to drain, clean and disinfect the equipment.
All 76 buildings later confirmed that they had completed the required remediation, city officials said. The Health Department also reported a steep decline in the onset of new illnesses after July 8.
Mayor Zohran Mamdani attributed the apparent containment of the cluster to what he described as “the aggressive strategy of early testing, enforcement, and remediation.”
“We have not seen anyone with new symptoms in over a week. We are focused on inspecting every cooling tower that tested positive and enforcing our laws to their fullest extent,” Health Commissioner Dr. Alister Martin said in a post on X Monday.
The outbreak has been concentrated in three Upper East Side ZIP codes: 10128, 10028 and 10075. The affected area includes the Carnegie Hill and Yorkville neighborhoods. Although New York typically records hundreds of Legionnaires’ disease cases each year, health officials said the clustering of cases in those neighborhoods represented a notable increase.
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People who have spent time in the affected area over the past several weeks are being urged to monitor themselves for symptoms, including fever, chills, fatigue, headaches, loss of appetite, confusion and diarrhea. Symptoms may not appear immediately and can develop up to 14 days after exposure, according to the Health Department.
Legionnaires’ disease is a form of pneumonia caused by inhaling water droplets or vapor contaminated with Legionella bacteria. Infections can also occur when contaminated water accidentally enters the lungs. The illness is not contagious and does not spread directly from one person to another.
Officials stressed that the current cluster is not associated with drinking water, showers or air-conditioning units. The Health Department said there is no problem with the plumbing systems in buildings within the affected ZIP codes. Residents can continue drinking tap water, bathing, showering, cooking and using their home air-conditioning systems as usual.
Cooling towers are used in refrigeration and building-cooling systems. They remove heat from buildings by drawing outside air across warm water supplied by a central chiller. The water is sprayed onto the fill material as fans pull air through the system, causing a small portion to evaporate and lowering the temperature of the remaining water.
That cooled water then circulates through the system again to absorb additional heat. When Legionella bacteria are present, however, contaminated mist or vapor released by the tower can potentially be inhaled by people nearby.
Research has found that Legionella bacteria can thrive in warm, wet environments. Cooling towers are particularly susceptible, along with hot tubs, spas, decorative fountains and certain plumbing systems. The bacteria occur naturally in freshwater, though they are generally present at levels too low to cause illness. They multiply most readily in warm water and environments with warm-to-hot temperatures, according to the Centers for Disease Control and Prevention.
When Legionella enters a building’s water system, it can potentially spread through equipment such as showerheads, faucets, hot-water tanks, heaters and cooling towers.
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Most people who encounter the bacteria do not become ill. The risk is higher, however, following substantial or repeated exposure, particularly among people who are more vulnerable to infection.
Those at greater risk include adults over 50, people who smoke or vape, people with weakened immune systems and those with underlying medical conditions. Diabetes and diseases affecting the heart, kidneys, liver or lungs can also increase the likelihood of severe illness. While most patients recover after receiving antibiotics, people who are immunocompromised or have chronic lung disease can develop potentially fatal complications.
Legionnaires’ disease can generally be treated with antibiotics, especially when it is identified early. There is no vaccine or preventive medication, and masks do not appear to protect against exposure, according to the New York City Health Department.
The national rate of Legionnaires’ disease has risen over the past decade, reaching 2.71 cases per 100,000 people in 2018, according to the CDC. Reported infections declined during the first year of the COVID-19 pandemic, only to increase again in 2021.
The latest cluster follows a deadly outbreak in Harlem last year that hospitalized 92 people and killed seven. Investigators also traced those cases to cooling towers.
That outbreak helped lead the city to adopt a new law in May requiring cooling towers to undergo more frequent inspections. The measure also increased fines for property owners who fail to comply with maintenance and safety requirements.
City Council Speaker Julie Menin, whose district includes the affected area, criticized failures to follow the city’s cooling-tower regulations.
“We know for a fact that many buildings did not comply with that City Council law, which is inexcusable. One of the many questions we have about the Health Department is, how many buildings did not comply? Let’s start with looking at those buildings.”
Officials are continuing to inspect every cooling tower that tested positive during the current outbreak and said enforcement efforts remain underway, despite indications that new infections have slowed significantly.
Moumita Basuroychowdhury is a Contributing Reporter at The National Digest. After earning an economics degree at Cornell University, she moved to NYC to pursue her MFA in creative writing. She enjoys reporting on science, business and culture news. You can reach her at moumita.b@thenationaldigest.com.
