Sixth Person Dies in New York City Legionnaires Disease Outbreak as Case Count Reaches 90 on East Side

A sixth person has died in connection with a monthlong cluster of Legionnaires' disease on Manhattan's Upper East Side, New York City health officials said Tuesday, as the outbreak's total case count held at 90 amid signs the underlying source of contamination has been brought under control.

At least 90 cases have been identified in the outbreak since it began in early July, according to the New York City Health Department, though no new cases have been diagnosed since July 17. Six people remain hospitalized, while 65 patients have been discharged since the cluster first emerged in the Carnegie Hill and Yorkville neighborhoods on the Upper East Side.

Health officials said dozens of cooling towers that tested positive for the presence of live Legionella bacteria, the pathogen responsible for the disease, have since been cleaned and disinfected. "We are confident the source of the Legionella bacteria has been eliminated," the health department said in a statement Tuesday.

The outbreak was first identified on July 2, when the department confirmed two Legionnaires' cases in close proximity in the affected ZIP codes, 10028, 10128 and 10075. Investigators went on to test 183 cooling towers across 160 buildings in the surrounding area, ultimately finding 77 that tested positive for the bacteria, a scale of contamination officials said was more than three times larger than that found during a similar outbreak in Central Harlem the previous summer, which was traced to just 12 towers across 10 buildings and led to at least six deaths and more than 100 diagnosed cases.

Legionnaires' disease is a severe form of pneumonia caused by inhaling small water droplets contaminated with Legionella bacteria, or by contaminated water accidentally entering the lungs, according to the Centers for Disease Control and Prevention. The bacteria occur naturally in freshwater environments but typically only reach concentrations capable of causing illness when they multiply in warm water systems, including cooling towers, hot water tanks, heaters, showerheads, sink faucets and other plumbing infrastructure in large buildings.

The disease does not spread from person to person. Infections generally occur when the bacteria enter a building's water supply and become aerosolized, allowing people nearby to inhale contaminated mist. Health officials have repeatedly stressed throughout the outbreak that the disease is unrelated to any building's plumbing system in the sense of tap water safety, and that residents in the affected neighborhoods can continue to safely drink tap water, shower, cook and run air conditioning.

Most patients recover from Legionnaires' disease with antibiotic treatment, but the illness can prove fatal in certain populations, including people who are immunocompromised, elderly, or living with chronic lung disease, according to the CDC. Those risk factors have been cited repeatedly by city officials this month in urging residents with flu-like symptoms, persistent cough, fever or difficulty breathing to seek prompt medical attention if they live, work or have spent time in the affected area since late June.

The Upper East Side cluster follows a pattern of recurring Legionnaires' outbreaks in New York City in recent years. A Central Harlem outbreak last summer sickened more than 100 people and killed at least six, prompting the city to authorize the hiring of 23 additional Legionella-focused water ecologists and inspection supervisors within the health department, bringing the intended total staffing level to 56. As of late July, the department's specialized Legionella team stood at 35 staff members, with another 14 in a monthslong process of training and shadowing veteran inspectors before being fully deployed, the department said in a statement.

Nationally, Legionnaires' disease has become more common over the past decade. Reported case rates climbed to a peak of 3.04 cases per 100,000 people in 2018, according to CDC surveillance data, before dropping during the first year of the COVID-19 pandemic and then rebounding by 2021. Public health researchers have pointed to aging building infrastructure, warming temperatures and improved disease surveillance and testing as possible contributors to the rising case counts recorded in recent years.

City officials under Mayor Zohran Mamdani's administration have taken a more aggressive regulatory approach to the outbreak than in some past investigations, requiring building owners to fully clean and disinfect any cooling tower that returns a positive result on an initial rapid screening test, rather than waiting roughly two weeks for slower culture testing to confirm the presence of live bacteria before mandating remediation. The administration also took the unusual step of publicly releasing the addresses of buildings whose cooling towers had tested positive, a transparency measure officials said was intended to keep residents informed in real time as the investigation progressed.

The New York City Health Department has continued to monitor the affected area for any new cases even after the apparent halt in transmission, and officials said they would provide further updates if additional cases or deaths are confirmed. Anyone experiencing symptoms consistent with Legionnaires' disease, including cough, fever, muscle aches and shortness of breath, is urged to contact a healthcare provider promptly, as early treatment with antibiotics significantly improves outcomes for most patients. Given that this involves an active public health situation, anyone personally concerned about symptoms or exposure risk should consult a medical professional directly rather than relying solely on general reporting.