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More testing alone won't prevent Legionnaires' outbreak, public health experts say
By
Joe Hong
Published Sep 18, 2025
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By
Joe Hong
Published Sep 18, 2025
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In the aftermath of this summer’s Legionnaires’ outbreak in Harlem that killed seven people and hospitalized 90, city lawmakers introduced new legislation that increases the number of times building owners are required to test their cooling towers, the main spreaders of the disease. But some public health experts say the sole focus on additional testing misses a need to enforce both maintenance requirements and the timing of the tests.
If the legislation passes, building owners will have to test for Legionella bacteria every 30 days, up from the current requirement of every 90 days, and every 14 days during heat-related emergencies.
But Abraham Cullom, director of water safety and management at Pace Analytical, said testing requirements that only mandate frequency leave open a loophole that building owners sometimes exploit in order to avoid bad results. He said cooling towers are often tested after they’re cleaned, which can generate a negative result that masks problematic towers that routinely develop dangerous levels of Legionella bacteria.
“You can throw as much testing at this as you want,” Cullom said. “If you’re not doing other things that are actually controlling Legionella, the testing itself isn’t going to protect anyone.”
He compared current testing requirements for cooling towers to the weigh-in process for boxers and wrestlers whose bodyweights are only measured at their all-time lows right before matches.
Janet Stout, a professor at the University of Pittsburgh and a leading expert on waterborne disease, recalled one water sample she received in her lab that smelled strongly of chlorine, an indication that it had been collected immediately after a cleaning. Her lab rejected the sample.
“When you test after a cleaning, all it does is confirm that you’ve cleaned the tower,” Stout said. “But if you test it before, it tells you whether or not your treatment program has been working.”
She said tests should instead be required before cleaning, that building owners should monitor their cooling towers on a weekly, if not daily, basis, and that the city should monitor owners to ensure they’re following the rules.
City Councilmember Lynn Schulman, who coauthored the legislation and chairs the Council's health committee, declined to comment on whether the Council will go beyond more frequent testing requirements. It’s scheduled to hold an oversight hearing on the city’s response to this summer's Legionnaires’ outbreak on Friday.
In an emailed statement, health department spokesperson Chantal Gomez said more frequent testing for Legionella will help detect unwanted bacterial growth earlier.
“Increasing Legionella testing from 90 to 30 days is a beneficial change but will not replace the mandates for routine monitoring and maintenance that are already required of building owners with cooling towers,” she said.
Current city laws require building owners to monitor the chemical and bacteriological content of the water running through their cooling towers. But building owners are only required to report test results for Legionella bacteria every 90 days.
Don Weiss, a former city health official, said the health department should require building owners to report daily or weekly test results. He said that would enable the city to better flag any towers with conditions that could potentially lead to a growth of Legionella, similar to the city’s current system for tracking communicable diseases.
“It would probably be a bit of an expense,” Weiss said. “But once you set the system up, it would work seamlessly.”
Cooling towers operate as a part of a building’s heating and cooling systems. They usually sit on top of roofs and circulate water throughout the building. The water absorbs heat from the building’s interior and returns to the cooling tower’s basin where fans evaporate the warm water.
The water can be a breeding ground for Legionella bacteria, especially at higher temperatures. If that bacteria becomes airborne with the water vapor and inhaled, it can cause Legionnaires’ disease.
After an outbreak in 2015, New York City lawmakers passed regulations that required all building owners to register their cooling towers with the city, hire professionals to manage them and create maintenance plans. The laws also authorized the city health department to inspect cooling towers and ensure that building owners are keeping records of their routine testing and cleanings.
A Gothamist analysis found that, in the months leading up to this summer’s outbreak, the city health department was on track to conduct less than half the number of inspections compared to 2017, when the city first implemented the regulations. Out of the approximately 5,000 towers registered with the city, about 30% had not been inspected since 2023.
The health department cited a shortage of inspectors in explaining the decrease. Gothamist found that there were fewer water ecologists this year compared to 2022 at the start of the Adams administration, despite the unit having more funding. At a late August press conference, Health Commissioner Michelle Morse said the city had enough staff to respond to the outbreak but will expand efforts to recruit more inspectors.
Stout said more regular city inspections could ensure building owners are following the spirit of the law rather than just abiding by the minimum reporting requirements.
“Someone has to be looking over their shoulder,” she said. “Perhaps the better answer is to better fund public health so it can do more inspections.”
This story has been updated with a statement from the city's Department of Health.
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Health and Science
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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