Legionnaires’ outbreak hits New York as officials rush to test water towers

For the past few days, Justine Kirby has been wearing an N95 mask every time she left her home for a walk in her quiet Upper East Side neighborhood.

He also keeps his apartment windows closed as the city’s Legionnaires’ disease outbreak, linked to contaminated water cooling towers, reaches 46 cases.

A cluster of Legionnaires’ infections, a serious form of pneumonia caused by Legionella bacteria, has caused alarm among community residents who packed City Hall at an Upper East Side church this week to pose a series of questions to New York City’s health department.

“There is a pretty high level of concern in the community,” Kirby said. “I’m the kind of person who likes to say the risk may be small, but [cleaning and disinfecting] “I don’t see much downside in taking these extra precautions.”

Health officials said that as of Wednesday evening, 22 people who were sick were hospitalized, some of them in intensive care.

Legionnaires’ is caused by bacteria that thrive in warm water, leading to flu-like symptoms that can sometimes be fatal if left untreated and in people with compromised immune systems.

D., professor of epidemiology at Columbia University Mailman School of Public Health. Wafaa El-Sadr said the current outbreak is caused by cooling towers in large buildings where Legionella bacteria live and multiply, infecting people when they breathe in the bacteria from the towers’ fog.

This week, the city announced its “aggressive” plan to combat the outbreak, saying it would work to test all water coolers in the area.

On Friday, New York City Mayor Zohran Mamdani said officials were testing all cooling towers in the area.

According to the BBC’s US partner CBS News, New York City Health Commissioner Alister Martin said the bacteria had been detected in 31 cooling towers in the area, 19 of which had their towers disinfected. The rest were expected to clear their towers by Saturday.

The towers, which are part of large air conditioning or cooling systems, cool indoor spaces by using water to remove heat from indoor air and evaporate it into the outdoor air as mist, according to the New York City health department. They are usually found on the roofs of buildings.

Instead of waiting for additional tests to confirm the presence of bacteria, officials said they want buildings to thoroughly clean and disinfect cooling towers after a single positive test result. According to the health ministry, some building owners have completed this process, while others are starting.

Speaking at a town hall at an Upper East Side church this week, Martin said it was good news that the city detected cases early.

“There are 160 cooling towers across this region that we’re looking at, and we’re not waiting,” he said. ABC News, external.

However, New York City Council Speaker Julie Menin said she was concerned that sufficient precautions were not taken.

He voiced his concerns at city hall and wrote a letter to Martin, saying he 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.”

Kirby said he was relieved by the steps the city’s health department was taking regarding testing.

But he added that he and the dozens of people who attended the town hall still have questions about how to best protect themselves. The city is telling people to monitor for symptoms and seek medical attention, including testing, if they have symptoms.

“They might reasonably say, ‘We don’t recommend that everyone wear a mask outside because the risk is low.’ But a well-fitting mask will protect you,” Kirby said. “I think they might be involved in this.”

The health department did not respond to a BBC request on whether residents would be advised to wear masks, but Dr. Al-Sadr said masking and closing windows could help those at the epicenter of the outbreak.

Dr El-Sadr said rising temperatures from climate change could worsen Legionnaires’ outbreaks, but the disease has plagued New York and other major cities around the world for decades.

In 2025, there were 105 cases of Legionnaires’ and five deaths in London, Ontario. Last August, 114 people were infected and seven died in Harlem in Upper Manhattan. The sources of the outbreak were later determined to be the cooling towers at Harlem Hospital and the area near the city’s new public health laboratory.

The Upper East Side is home to a large number of cooling towers, more than three times the number of towers the city tested during the 2025 Harlem outbreak, according to the New York City Department of Health and Mental Hygiene.