Respiratory outbreaks can move remarkably fast in crowded cities, as demonstrated by a recent Legionnaires’ disease outbreak on Manhattan’s Upper East Side. Health officials confirmed in July 2026 that a fourth person had tragically passed away from the illness, which has infected at least 76 residents across the 10028, 10075 and 10128 ZIP codes.
The primary culprit behind the spread was Legionella bacteria carried in fine water mists from building cooling towers. In response to the spike in cases, city inspectors sampled 183 cooling towers in the affected neighborhoods, identified 76 buildings with positive tests and immediately ordered full disinfection. Fortunately, health officials believe the main source of exposure has been successfully eliminated through these swift remediation efforts.
NYC Health Commissioner Dr. Alister Martin offered condolences to those affected while reassuring the public. “At this time, we believe any source of exposure has likely been eliminated. We have not seen anyone with new symptoms in over a week,” she confirmed. “We are focused on inspecting every cooling tower that tested positive and enforcing our laws to their fullest extent.”
While the immediate risk appears to have subsided, this outbreak serves as a clear reminder of how quickly airborne water mist can impact public safety. Understanding how Legionnaires’ disease spreads, recognizing its initial symptoms, and knowing when to seek medical care remain essential steps for staying safe in an urban environment.
What is Legionnaires’ disease?
Legionnaires’ disease is an acute and serious form of atypical pneumonia (lung infection) that is caused by Legionella bacteria, which are most often of the species Legionella pneumophila. The disease was named after an epidemic in 1976 at an American Legion convention in Philadelphia, which led to the identification of the unknown bacterium.
According to the Centers for Disease Control and Prevention (CDC), Legionella bacteria exist naturally in freshwater environments like lakes and streams. The bacteria pose a serious human health risk when they contaminate and proliferate in complex water systems. These include commercial misting devices, hot tubs, decorative fountains, large building plumbing systems and industrial cooling towers.
Legionnaires’ disease cannot be transmitted from one person to another. Rather, infection is acquired when a person breathes the live bacteria, in microscopic droplets of water mist or vapor in the air.
What’s happening in your body
Legionella enters the body when a person inhales water droplets containing the bacteria, suspended in the air as an aerosol. When the bacteria move to the lower respiratory tract, the body’s immune system mobilizes specialized white blood cells called alveolar macrophages to ingest the bacteria, according to the research published by the National Institutes of Health (NIH).
Legionella has a special way of preventing these immune cells from killing it. Instead, the bacteria exploit the macrophages by turning them into host cells and multiply fast. When the infected cells burst open, new bacteria are released, triggering a strong inflammatory response. This inflammation results in fluid, pus and cellular debris filling the alveoli, so that the lungs can no longer effectively move oxygen into the bloodstream. The outcome is severe bacterial pneumonia with systemic inflammation.
Causes of Legionnaires’ disease
Growth and dissemination of the Legionella bacteria in warm and stagnant water systems is the main cause of Legionnaires’ disease. The bacteria grow at optimum temperature ranges of 68°F to 122°F (20°C to 50°C) in water, according to the World Health Organization.
Large building cooling towers, which evaporate water and release heat into the air, are common sources of exposure. Bacterial growth and aerosolization are also common in commercial hot tubs and spas, where warm water and splashing jets provide the perfect environment.
Bacteria also thrive in systems with extensive plumbing, such as hot water tanks, large recirculation pipes and low-flow showerheads, where water is continually stagnant, or in decorative fountains and misters that spray fine mist in hospitals, hotels or apartment complexes.
Not all individuals who are exposed to Legionella actually get sick. People over age 50, or current or former smokers and vapers, are at a much greater risk for developing Legionnaires’ disease, according to the American Lung Association.
Furthermore, people who suffer from chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) or emphysema or those who have a weakened immune system due to cancer, kidney failure, diabetes or immunosuppressive medications, carry an elevated risk.
Health risks and complications
Legionnaires’ disease is a serious disease that can rapidly deteriorate to become a life-threatening systemic disease if not treated early with the proper antibiotic.
The Mayo Clinic reports that one of the most serious complications of Legionnaires’ disease is acute respiratory failure, in which the lungs become so waterlogged that they cannot get enough oxygen into the bloodstream or remove carbon dioxide, and mechanical ventilation is needed.
Healthcare Policy Analyst Anne Kamwila tells Blavity Health, “The infection can also lead to septic shock, a massive immune response that leads to a dramatic decrease in blood pressure and deprives organs of oxygen-rich blood. In addition, acute kidney injury, which occurs in severe cases of hypotension and systemic toxicity, causes the kidneys to stop filtering waste products from the blood, ultimately resulting in progressive multiorgan failure, including the lungs, heart, and kidneys.”
The CDC estimates that about 1 in 10 people who develop Legionnaires’ disease will die from the disease. The mortality rate increases to about 25% if people become infected in a health care setting.
What to do about Legionnaires’ disease symptoms
Legionnaires’ disease can cause symptoms that resemble those of other serious pneumonias or influenza, so prompt clinical assessment is important. No over-the-counter medications can cure a Legionella infection; prescription antibiotics are required for effective management.
It’s important to note that Legionnaires’ disease symptoms can manifest 2 to 14 days after inhaling water mist that is contaminated with the bacteria. If you have recently been in an area with an active community cluster (Upper East Side ZIP codes 10028, 10075 or 10128) and develop flu-like symptoms, notify your healthcare professional right away. Prompt antibiotic therapy can improve recovery outcomes.
When to see a doctor
If you have a high fever, severe cough or trouble breathing, get medical attention immediately if you have been in an area where Legionnaires’ is known to have occurred or if you are in a high-risk group.
The Mayo Clinic and CDC say the initial symptoms typically appear within 2-10 days after exposure and include high fever, severe chills, muscle aches, joint pain, headache and overall fatigue. As the infection worsens and goes deeper into the lungs, other symptoms appear, such as coughing, which may be accompanied by the production of mucus or small amounts of blood; shortness of breath or tightness of the chest; nausea; vomiting; watery diarrhea; and confusion or mental changes, especially in older people.
If you are having trouble breathing, if you have crushing chest pain, if you have a high fever and are confused, if your lips and skin are blue, emergency medical care is necessary.
How do I know if my water has Legionnaires’?
Legionella bacteria cannot be detected by the naked eye, by odor or by taste. The bacteria are invisible to the naked eye and do not affect the taste, smell or clarity of tap water.
If Legionella is suspected, a water sample can be collected and tested in a certified laboratory using specialized techniques, including culture testing or polymerase chain reaction (PCR) assays, to confirm the presence of Legionella.
Health officials note that municipal tap water is safe during community clusters linked to cooling towers, such as the one in the Upper East Side. It is not possible to contract Legionnaires’ disease from drinking tap water, cooking with water or using home window air conditioners.
Unlike other air conditioners, home AC units do not create mist or require standing water to cool air indoors. When clusters of Legionnaires’ disease are clearly linked to an internal hot water plumbing system in a building, however, health departments may recommend that people take temporary precautions with hot showerheads and faucets until the water system is remediated.
Bottom line
Legionnaires’ disease is a severe, non-contagious bacterial pneumonia that is acquired by breathing in bacteria-laden water aerosolized from a cooling tower or hot tub. Although recent outbreaks, such as the one on New York’s Upper East Side, teach us how serious the disease can be, the bacteria can be effectively treated if detected early. Persons with potential exposure who develop a fever, cough or difficulty breathing should get urgent medical evaluation and testing and a course of antibiotic treatment.
Frequently Asked Questions
What is the most common way to catch Legionnaires’ disease?
The most common way to catch Legionnaires’ disease is by inhaling microscopic airborne water droplets or mist contaminated with live Legionella bacteria.
Which antibiotic is used to treat Legionnaires’ disease?
Legionnaires’ disease is most commonly treated using macrolide antibiotics (such as azithromycin) or fluoroquinolones (such as levofloxacin), which effectively penetrate human lung cells to destroy the bacteria.
Citations
New York C. 4th death related to UES Legionnaires” disease outbreak confirmed. CBS News. Published July 20, 2026. https://www.cbsnews.com/newyork/video/4th-death-related-to-ues-legionnaires-disease-outbreak-confirmed/
CDC. How Legionella Spreads.; 2024. https://www.cdc.gov/legionella/causes/index.html
Atefe Panahipoor Javaherdehi, Ghanbari S, Mahdavi P, Alireza Zafarani, Mohammad Hossein Razizadeh. The role of alveolar macrophages in viral respiratory infections and their therapeutic implications. Biochemistry and Biophysics Reports. 2024;40:101826-101826. doi:10.1016/j.bbrep.2024.101826
World Health Organization. Legionellosis. World Health Organization: WHO; 2022. https://www.who.int/news-room/fact-sheets/detail/legionellosis
American Lung Association. Learn About Legionnaires’ Disease. 2018. https://www.lung.org/lung-health-diseases/lung-disease-lookup/legionnaires-disease/learn-about-legionnaires-disease
Mayo Clinic. Legionnaires” Disease – Symptoms and Causes.; 2021. https://www.mayoclinic.org/diseases-conditions/legionnaires-disease/symptoms-causes/syc-20351747
CDC. About Legionnaires Disease and Pontiac Fever.; 2024. https://www.cdc.gov/legionella/about/index.html