Each year, between 200 and 700 New Yorkers are diagnosed with Legionnaires’ disease, a severe form of pneumonia caused by exposure to Legionella bacteria. In 2019, 438 cases were reported, predominantly in the Bronx. Last year, there was an outbreak in Harlem where four people died, 100 people were sickened, and 17 were hospitalized.
This summer, the outbreak is concentrated in the Carnegie Hill and Yorkville neighborhoods. It has sickened 82 people and resulted in five deaths. After testing 183 buildings, city health officials have identified Legionella bacteria in cooling towers at 34 buildings and are overseeing cleaning and disinfection efforts.
Fortunately, the rate of contraction appears to be diminishing. Nevertheless, this summer's outbreak has renewed concerns and questions about Legionnaires' disease and how New York City’s residential and commercial buildings manage one of their most important but often overlooked systems: cooling towers.
How is Legionnaires' disease spread, and who is at risk?
Legionella bacteria grow in warm water environments and can become a health risk when contaminated water is released into the air as tiny droplets or mist. People typically become infected by breathing in contaminated aerosols from sources such as cooling towers, hot tubs, or large building water systems. The disease is not spread through person-to-person contact.
Although healthy people exposed to Legionella often do not become ill, older adults, smokers, people with chronic lung conditions, and those with weakened immune systems are at higher risk for serious complications.
According to a NYC.gov report, neighborhoods with higher rates of Legionnaires’ disease often have older residents and greater levels of poverty. Communities with predominantly Black and Latino populations experience a disproportionate impact, reflecting broader inequities linked to long-standing structural factors. Risk can also vary based on neighborhood conditions, including building density, infrastructure age, water system design, maintenance practices, and the location of potential Legionella sources. Differences in testing and detection may also influence reported rates.
Legionnaires' disease and cooling towers
Cooling towers are essential components of many of New York’s largest residential and commercial buildings. They help remove heat from air-conditioning systems, but they also rely on water circulation, creating an environment where bacteria can grow if systems are not properly maintained. They are susceptible to bacterial infection when they are improperly cleaned or maintained.
During New York’s hot, humid summers, water temperatures can reach levels that allow Legionella to multiply. When cooling towers release water vapor or mist into the air, contaminated droplets can potentially spread beyond the building itself, which is why the outbreak happens in clusters.
New York City has some of the most stringent cooling tower regulations in the nation, yet Legionnaires’ disease remains a recurring public health concern. Following a Legionnaires’ outbreak in the Bronx in 2015, the city implemented rules requiring building owners to:
- Register cooling towers with the city
- Maintain water management plans
- Conduct routine inspections and testing
- Clean and disinfect systems regularly
- Keep detailed maintenance records
Earlier this year, the city increased testing requirements and expanded inspection resources. However, the current outbreak shows that even rigorous regulations cannot completely eliminate risk.
Prominent institutions affected by the recent testing have emphasized their ongoing maintenance programs. The Guggenheim Museum, for example, has stated that its cooling tower is tested and treated monthly by an outside company.
Cooling towers, boilers, plumbing systems, and mechanical equipment are essential to modern high-rise living, but they also require careful maintenance and oversight. For building owners, boards, and property managers, the outbreak underscores the importance of proactive water management and strict compliance with city regulations.
In a city defined by its towers, maintaining what happens inside and on top of those buildings remains a critical part of protecting the people who live and work below.
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Contributing Writer
Michelle Sinclair Colman
Michelle writes children's books and also writes articles about architecture, design and real estate. Those two passions came together in Michelle's first children's book, "Urban Babies Wear Black." Michelle has a Master's degree in Sociology from the University of Minnesota and a Master's degree in the Cities Program from the London School of Economics.
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