RESOLVING THE LEDGER
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A non-profit newsroom, powered by WNYC. Gothamist Listen Live Donate News Officials identify UES cooling towers that had living Legionella bacteria before outbreak By Joe Hong Published Jul 27, 2026 at 2:38 p.m. ET
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New York City’s Health Department has identified 56 buildings on the Upper East Side that had active Legionella bacteria living in their cooling towers before an outbreak of Legionnaires’ disease that has so far killed five people. The finding is a result of a more detailed round of testing that brings health officials one step closer to homing in on the outbreak’s original source.
As part of the health department’s investigation, it collected culture samples from all cooling towers in the three ZIP codes affected by the outbreak. Cooling towers are part of a building’s air conditioning system that can spread dangerous Legionella bacteria if not properly maintained. The samples were sent to labs for analysis.
Culture tests take several weeks to produce results and are more accurate than the initial round of rapid PCR test results released by the city earlier this month. That first round of testing showed 76 buildings with some trace of both living and dead bacteria.
“We are narrowing it down,” said Chantal Gomez, a spokesperson for the health department. She said the live bacteria from the culture tests will be further examined and compared to samples taken from patients. Only then will the health department be able to definitively identify the original source or sources of the outbreak.
Gothamist has mapped the results for each round of testing:
As of Monday, a total of 89 people have been sickened in this year’s outbreak.
Gomez said the source of the outbreak has likely been eliminated.
“Building owners drained their cooling towers after the PCR tests, and we haven’t seen any new diagnoses,” she said.
New York City’s regulations require building owners to conduct culture tests every 31 days. The health department makes an effort to inspect every cooling tower annually. But compliance with testing requirements has lagged, and health officials have struggled to meet their inspection goals due to staffing shortages.
A Gothamist analysis last year found that inspections had reached a record low ahead of an outbreak in Harlem last summer. Inspection records had only slightly improved before this year’s outbreak on the Upper East Side, despite efforts by the health department to increase its number of cooling tower inspectors.
According to updated data from the city, only 56% of cooling towers received inspections in the past year as of June 17, and 82% have submitted Legionella test results as of July 24.
Among the 56 towers that tested positive on the culture test, only 52% had been inspected in the past year, and 86% had submitted Legionella test results.
Gomez said that a positive culture test result does not necessarily mean that the building owner was not compliant with city regulations. The bacteria could have grown in the days or weeks immediately following a routine test, she said.
Twelve buildings are still awaiting culture test results. Gomez said the health department was only able to test a certain number of cooling towers each day after the outbreak began. Testing for some buildings was delayed. She added that the labs that conduct the culture tests also have limited capacity.
City Council Speaker Julie Menin has criticized the Mamdani administration for its lack of transparency in its handling of the outbreak. Menin had urged the health department to disinfect all cooling towers in the affected ZIP codes.
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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