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What we still don’t know about NYC's deadly Legionnaires’ outbreak, ahead of hearing
By
Joe Hong
Published Sep 19, 2025
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Michael Appleton/Mayoral Photography Office
By
Joe Hong
Published Sep 19, 2025
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City councilmembers will hear testimony from city health officials for the first time since a deadly Legionnaires' outbreak in Harlem this summer killed seven people and sickened 114.
Representatives from the Department of Health and Mental Hygiene and NYC Health and Hospitals are scheduled to answer questions about the outbreak, though officials from Health and Hospitals abruptly canceled their planned attendance at a public land use hearing on Thursday.
The city pinpointed cooling towers at two sites as the origin of the outbreak: Harlem Hospital — where another cooling tower had been linked to a previous outbreak in 2021 — and a construction site for a public health lab owned by the city and managed by the construction firm Skanska USA.
New York City has some of the country's toughest regulations designed to prevent the spread of Legionnaires' disease. They were passed in response to an outbreak in 2015 and primarily focus on cooling towers, which operate as part of buildings’ heating and cooling systems and are the main vectors for the disease.
Despite those strict laws, the city has continued to experience sporadic outbreaks during warmer months, particularly in low-income neighborhoods.
The Council's health committee is likely to grill health officials for further details on how the outbreak started and what the city did to protect New Yorkers. The hearing starts at 10 a.m. Here are some of the questions we still don’t have answers to.
What protocols did Health and Hospitals have for maintaining its cooling towers at the Harlem Hospital?
Spokespeople for both Health and Hospitals and City Hall have said Harlem Hospital “exceeded the requirements” of New York City’s cooling tower regulations. According to public data and hospital officials, the hospital tested the tower in March and June for Legionella bacteria and disinfected it on July 2 as a part of routine maintenance, three weeks before the first case was reported.
But public health experts say Legionella can easily reach dangerous levels in three weeks, especially during warmer months. Officials from both City Hall and the hospital are adamant that the hospital was in full compliance, but experts who spoke with Gothamist are skeptical.
Don Weiss, a former city health official, said Legionella would not have thrived if the hospital had been doing everything it’s supposed to, including daily and weekly chemical and bacteriological monitoring. The city has declined multiple times to provide documentation of the daily and weekly monitoring of the cooling tower.
The hospital had not uploaded any of the testing records onto the city’s public cooling tower portal as of last week when the city’s health department blocked public access to the portal. Chantal Gomez, a spokesperson for the department, cited “a bad actor” who had created multiple fake accounts and was using an automated bot to download data.
What was the cause of the 2021 outbreak that was linked to a different cooling tower at the hospital? Did the same issue lead to the 2025 outbreak?
Back in 2021, health officials linked a different cooling tower at the same hospital in Harlem to an outbreak that hospitalized nine people. City Hall, Health and Hospitals, and the Department of Health and Mental Hygiene have refused to provide any details about the causes of that outbreak. It remains unclear whether any similar lapses in oversight caused the 2021 and 2025 outbreaks.
Why didn’t the city realize its own contractor at the construction site had failed to register a cooling tower?
A spokesperson from the health department said an investigation by the agency found “lapses in required maintenance, monitoring and testing of the cooling tower” and the “day-to-day oversight” of the tower at the Skanska USA construction site.
The cooling tower at the construction site had not been registered with the city, as is required by law, when Skanska USA began using it in June. According to a spokesperson from City Hall, Skanska “took immediate action” after learning that it needed to be registered. The spokesperson also said Skanska’s contract with the city requires it to manage the cooling tower.
Did the city respond quickly and adequately enough?
At the start of the 2015 Legionnaires’ outbreak that ultimately killed 16 people, the Department of Health and Mental Hygiene activated its “incident emergency command” protocol, according to multiple former health officials who worked at the department at the time.
According Chris Boyd, a former health official, the protocol enables the agency to set up a “war room” and tap resources from across the city, while also involving the mayor’s office more closely on communications. The health department said it did not find the protocol necessary for this summer’s outbreak.
The agency announced its investigation through several social media posts on July 25. But according to a timeline provided by the agency, the department didn’t start setting up tables in Harlem to talk with residents and distribute flyers until Aug. 1, nearly a week later.
On Aug. 4, the agency identified 11 cooling towers that had tested positive for Legionella. But it waited until Aug. 14 to release the addresses for those towers.
Health Commissioner Michelle Morse previously told WNYC that health officials didn't want to worry the addresses' residents or create a false sense of security among people who don't live at the addresses.
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Politics
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new york city
Joe Hong
Joe Hong is the investigative data reporter for WNYC and Gothamist. He previously covered K-12 education for several newsrooms across California. His reporting has led to local reforms in juvenile justice system as well as a state law requiring universal screening for dyslexia. Got a tip? Email [email protected]
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