For the past few days, Justine Kirby has been sporting an N95 mask every time she leaves her house to walk in her quiet Upper East Side neighbourhood.
She is keeping her apartment windows closed, too, as an outbreak of Legionnaires’ disease grows to 46 cases, which the city has linked to contaminated water cooling towers.
The cluster of Legionnaires’ infections – a serious type of pneumonia caused by Legionella bacteria – has raised alarms among residents in the community, who packed a town hall in an Upper East side church this week to pose a series of questions to New York City’s health department.
“There is quite a level of concern in the community,” Kirby said. “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.”
As of Wednesday evening, 22 people who were sick had gone to hospital, some treated in the intensive care unit, health officials have said.
Legionnaires’ is caused by bacteria that grow in warm water, leading to flu-like symptoms that can sometimes be fatal without treatment and for those who are immunocompromised.
The current outbreak is caused by cooling towers from larger buildings where Legionella bacteria live and multiply, infecting people when they breathe in the bacteria from the mist of the towers, said Dr Wafaa El-Sadr, a professor of epidemiology at Columbia University Mailman School of Public Health.
This week, the city announced an “aggressive” plan to tackle the outbreak. On Friday, New York City Mayor Zohran Mamdani said officials had tested all of the cooling towers in the area.
New York City Health Commissioner Alister Martin said the bacteria was detected in 31 towers in the area, and 19 had already been disinfected, according to the BBC’s US partner CBS News. The rest of the buildings were expected to clean their towers by Saturday.
Part of large air conditioning or refrigeration systems, the towers cool indoor spaces by removing heat from the air using water and evaporating it as mist into the outdoor air, according to the New York City health department. They are often found on top of buildings.
Officials have said they are requiring buildings to fully clean and disinfect their cooling towers after one positive test result, instead of waiting for additional testing to confirm the presence of the bacteria.
At the town hall at the church this week, Martin said it was good news the city had identified the cases early.
“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, according to ABC News, external.
But Julie Menin, the speaker of the New York City Council, said she was worried not enough action had been taken.
She wrote in a letter to Martin that 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”.
Kirby said she was comforted by actions the city’s health department was taking in terms of testing, but added she and many of the dozens who attended the town hall still had questions about protecting themselves.
The city has told people to monitor for symptoms and seek medical care, including testing, if symptomatic.
“They could quite reasonably say, ‘Because risk is low, we’re not recommending everyone mask outside. However a good well-fitted mask will protect you,'” Kirby said. “I think they could’ve gotten into that.”
The health department did not respond to a request from the BBC about whether they advised local residents to wear a mask, but Dr El-Sadr said masking – and closing windows – could help for those in the epicentre of the outbreak.
Dr El-Sadr said warming temperatures from climate change could worsen Legionnaires’ outbreaks, though the disease has plagued New York and other major cities around the world for decades.
In 2025, London, Ontario, saw 105 cases of Legionnaires’ and five deaths. Last August, in Harlem in upper Manhattan, 114 people were infected and seven people died. The sources of the 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, according to the New York City Department of Health and Mental Hygiene.
