An outbreak of legionnaires’ disease in New York City has claimed a fourth life, officials have said, as they again expressed confidence the source of the exposure had been eliminated.

A statement from the city’s health department on Monday said the outbreak, which was traced to cooling towers in buildings in Manhattan’s Upper East Side, had sickened 76 people – with 53 discharged after hospital treatment, and 12 others managing their recovery at home.

A graph accompanying the press release showed the most recent diagnosis of the cluster was on 15 July, with the peak of the outbreak occurring a week earlier when 13 infections were confirmed.

“At this time, we believe any source of exposure has likely been eliminated,” Dr Alister Martin, health commissioner of New York City, said in a post on X on Monday afternoon.

“We have not seen anyone with new symptoms in over a week. We are focused on inspecting every cooling tower that tested positive and enforcing our laws to their fullest extent.”

As in the three previously reported deaths, authorities revealed no details about the fourth victim. Martin said: “We mourn their passing, and our thoughts are with their family and loved ones.”

Legionnaires’ disease, a serious form of pneumonia, is treatable but kills about 10% of patients, according to the US Centers for Disease Control and Prevention (CDC). The Legionella bacterium that causes the sickness grows in warm water and can proliferate in cooling towers, hot tubs and showerheads.

Health officials believe the source of the “community cluster” causing the outbreak in New York City was buildings in the Upper East Side neighborhoods of Carnegie Hill and Yorkville. In all, 76 buildings tested positive for either living or dead Legionella bacteria in cooling towers, including museums, private schools and apartment houses. Their owners were ordered to drain and sanitize cooling systems.

“This is not an issue with any building’s plumbing system,” the statement from the NYC health department said.

“Residents can continue to drink tap water, bathe, shower, cook, and use your air conditioner at home.

“Any New Yorkers who currently live or work in this area or people who have visited the area since late June and are experiencing flu-like symptoms, such as cough, fever, or difficulty breathing should contact a health care provider immediately.”

People can contract legionnaires’ disease by inhaling tiny droplets of contaminated water. It does not spread person to person.

A previous outbreak in Harlem in August 2025 killed seven people and sickened more than 100. That episode followed a similar pattern with new cases trailing off quickly after the source was identified and eliminated, and officials declared the outbreak over after about three weeks.

New York mayor, Zohran Mamdani, addressed the latest outbreak in remarks at an event for small businesses on Monday.

“I’m heartbroken by the loss of our fellow New Yorkers and send my deepest condolences to their loved ones,” he said.

Mamdani said city officials began tracking the outbreak on 2 July after two confirmed cases. “Following the guidance of public health experts, we directed every building with an initial positive test result to immediately clean and disinfect its cooling tower,” he said.

“Due to the aggressive strategy of early testing, enforcement and remediation, we believe that we have now eliminated the source of exposure. We are continuing to inspect cooling towers and will aggressively enforce our public health laws.”