New York City Investigates 46 Legionnaires’ Cases Tied to Cooling Towers

New York City health officials are working to contain a cluster of Legionnaires’ disease on the Upper East Side that has sickened 46 people, with 22 individuals currently hospitalized. The outbreak, which was first identified and announced on July 2, has been traced to contaminated cooling towers—the large devices often found on rooftops that function as part of a building’s air conditioning system.

As of late Thursday, health officials have zeroed in on 19 “buildings of interest” in the area after their respective cooling towers preliminarily tested positive for Legionella bacteria. While the city continues its investigation, all 19 buildings have been ordered to drain, clean, and disinfect their towers as a precautionary measure.

Understanding the Source of the Outbreak

Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria, which thrive in stagnant, warm water. The disease is not contagious through person-to-person contact. Instead, it is contracted when people inhale fine water droplets or mist released into the air by cooling towers.

Experts note that cooling towers act as vents for air conditioning systems, pushing hot air outdoors. These devices do not interact with a building’s internal plumbing or drinking water supply. Health officials have emphasized that residents in the impacted area can continue to use their tap water, shower, cook, and operate air conditioners safely.

The current area of concern covers three ZIP codes: 10075, 10028, and 10128, stretching from approximately 76th Street to 97th Street.

Regulatory Compliance and Inspection Challenges

The outbreak has brought renewed scrutiny to the maintenance of the city’s nearly 5,000 cooling towers. Under current city law, building owners are required to test for Legionella monthly and develop detailed maintenance plans to prevent contamination.

Data analysis reveals gaps in oversight. While the city health department has identified 160 cooling towers within the affected ZIP codes, a Gothamist analysis of registration data found 203 active towers in the same area. Furthermore, public data indicates that about half of the cooling towers in these neighborhoods have gone over a year without a city inspection, a rate consistent with cooling towers citywide. As of May, 55% of the 203 active towers in the affected ZIP codes had reported 2026 test results to the health department.

Regarding the city’s inspection efforts, officials have noted that they have struggled to meet the goal of annual inspections for all towers due to a shortage of inspectors.

Debate Over Proactive Disinfection

A point of friction has emerged between City Council Speaker Julie Menin and the New York City Department of Health and Mental Hygiene regarding how to manage the response. Speaker Menin has urged the city to proactively disinfect all cooling towers in the affected area, regardless of test results, to prevent further illness.

The Health Department, however, has pushed back against this suggestion, stating that disinfecting a tower before a sample is collected makes it impossible to trace the source of the infection. The agency maintains that it has been “aggressively” identifying and ordering the disinfection of towers that test positive for the bacteria.

Mayor Zohran Mamdani has committed to increasing transparency by publishing the locations of all cooling towers that test positive for Legionella as soon as results become available.

Guidance for Residents and Vulnerable Populations

Health officials are urging anyone who has visited the affected neighborhoods in recent weeks and is experiencing flu-like symptoms to seek immediate medical attention. The risk of serious illness is higher for the elderly and those who are immunocompromised. Census data shows that the Carnegie Hill neighborhood, located within the impacted zone, has a significantly higher proportion of residents aged 65 or older (29%) compared to the citywide average (15%).

Microbiologist Janet Stout, a Legionella expert, suggests that residents concerned about their buildings should ask owners if testing and maintenance are up to date. While some residents have begun wearing masks or keeping windows closed in response to the cluster, the health department is not currently advising changes to daily routines or the use of masks.

The city continues to monitor the situation, with health workers distributing information at senior centers in the vicinity of the outbreak to ensure that those at the highest risk receive proper guidance.

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