For the past few days, Justine Kirby has been wearing an N95 mask every time she leaves her house to walk around her quiet Upper East Side neighborhood.

He also keeps his apartment windows closed 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 sparked alarm among community residents, who packed a town hall at an Upper East Side church this week to pose a series of questions to the New York City health department.

“There is a high level of concern in the community,” Kirby said. “I’m the kind of person who likes to say that the risk may be small, but until [cleaning and disinfecting] “Once that’s done, I don’t see many downsides to taking these additional measures.”

As of Wednesday night, 22 sick people had been admitted to the hospital, some of whom were in the intensive care unit, health officials said.

Legionnaires’ disease is caused by bacteria that grow in warm water, causing flu-like symptoms that can sometimes be fatal without treatment and for those who are immunocompromised.

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

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

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

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, according to BBC US partner CBS News. The rest were expected to clear their towers on Saturday.

As part of large air conditioning or refrigeration systems, towers cool indoor spaces by removing heat from indoor air using water and evaporating it as fog to the outside 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 a positive test result, rather than waiting for additional testing to confirm the presence of the bacteria. Several building owners have already completed that process, while others are just getting started, according to the health department.

At the Upper East Side church town hall this week, Martin said it was good news that the city had identified the cases early.

“What we have in front of us is 160 cooling towers across this region that we’re looking at and we’re not waiting,” he said, according to ABC News., external.

But Julie Menin, president of the New York City Council, said she was concerned that not enough action had been taken.

She raised her concerns at City Hall and wrote a letter to Martin saying she was “deeply concerned that the Department of Health and Mental Hygiene has not yet required building owners to proactively disinfect all cooling towers in the area under investigation.”

Kirby said she was comforted by the actions the city health department was taking in terms of testing.

But she added that she and many of the dozens of people who attended the town hall still had questions about how to best protect themselves. The city has been telling people to monitor symptoms and seek medical care, including testing, if they have symptoms.

“They could quite reasonably say, ‘Because the risk is low, we don’t recommend that everyone wear a mask outside. However, a well-fitting mask will protect you,'” Kirby said. “I think they might have gotten into that.”

The health department did not respond to a BBC question about whether they advised local residents to wear masks, but Dr El-Sadr said wearing a mask (and closing windows) could help those at the epicenter of the outbreak.

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

In 2025, London, Ontario, recorded 105 Legionnaires’ cases and five deaths. Last August, in Harlem, in Upper Manhattan, 114 people were infected and seven died. The sources of the outbreak were later identified as Harlem Hospital’s cooling towers 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 triple the number the city tested during the 2025 Harlem outbreak, according to the New York City Department of Health and Mental Hygiene.