An outbreak of Legionnaires' disease on Manhattan's Upper East Side has infected 46 people, and city officials are testing cooling towers to find sources, health officials said.
As of Wednesday evening, 22 people who were sick had gone to hospital, some of whom were in the intensive care unit, health officials said.
New York City Mayor Zohran Mamdani said officials had tested all of the cooling towers in the area on Friday. New York City Health Commissioner Alister Martin said the bacteria was detected in 31 cooling towers in the area, including 19 buildings that had already disinfected their towers, and said the rest were expected to clean their towers by Saturday.
Martin told a town hall, "What we have in front of us is 160 cooling towers across this region that we are looking at, and we are not waiting," he said.
The health department is requiring buildings to fully clean and disinfect their cooling towers after one positive test result, instead of waiting for additional testing, and several building owners have already completed that process while others are starting, the health department said. Cooling towers are part of large air conditioning or refrigeration systems that cool indoor spaces by removing heat from indoor air using water and evaporating it as mist into the outdoor air, the health department said.
Julie Menin, the speaker of the New York City Council, said she was worried not enough action had been taken at the town hall and wrote a letter to Martin saying she was "deeply concerned that the Department of Mental Health and Hygiene has still failed to require building owners to proactively disinfect all cooling towers in the area under investigation."
Justine Kirby, a resident of the Upper East Side, said she has been wearing an N95 mask every time she leaves her house and is keeping her apartment windows closed. "I'm the sort of person who likes to say that the risk may be small, but until the [cleaning and disinfecting] is done, I don't see much downside in taking these extra measures," she said.
Dr Wafaa El-Sadr, a professor of epidemiology at Columbia University Mailman School of Public Health, said the current outbreak is caused by cooling towers where Legionella bacteria live and multiply, infecting people when they breathe in the bacteria from the mist of the towers, and she said masking "- and closing windows - could help for those in the epicentre of the outbreak." Dr El-Sadr also said that warming temperatures from climate change could worsen Legionnaires' outbreaks. In 2025, London, Ontario, saw 105 cases of Legionnaires' and five deaths, and last August in Harlem 114 people were infected and seven people died; the sources of that outbreak were later identified as cooling towers at Harlem Hospital and the nearby site of the city's new public health laboratory. The Upper East Side is home to a large number of cooling towers, more than three times as many towers that the city tested during the 2025 Harlem outbreak, the health department said.