Legionnaires' Disease Outbreak

Source of Infection

The outbreak has been linked to Legionella bacteria detected in cooling towers across multiple buildings in the affected area. Cooling towers can release fine water droplets or mist into the surrounding air. People may become infected when they inhale droplets containing the bacteria.

The New York City Health Department conducted testing of 183 cooling towers associated with approximately 160 buildings in and around the affected neighbourhoods. Confirmatory culture testing detected live Legionella pneumophila bacteria in 34 cooling towers located at 33 buildings.

The buildings investigated included:

• Residential apartment buildings
• Schools and educational institutions
• Museums and cultural institutions
• Commercial buildings
• Other properties operating cooling-tower systems

All cooling towers confirmed to contain live Legionella bacteria completed the required cleaning and remediation. Health officials believe that the primary source of exposure has likely been eliminated, although epidemiological investigations and laboratory analyses are continuing.

Important: A cooling tower testing positive for Legionella does not, by itself, establish that a particular building was the source of a person's infection. Additional epidemiological and laboratory evidence is required to establish such a connection.

Public Health Response

The New York City Health Department has implemented an extensive outbreak investigation and response, including:

• Conducting extensive PCR and culture testing of cooling towers in the affected neighbourhoods
• Ordering immediate cleaning, disinfection, and remediation of cooling towers with positive test results
• Verifying that contaminated cooling-tower systems completed the required remediation
• Increasing inspections and enforcement of cooling-tower regulations
• Reviewing cooling-tower maintenance, testing, and compliance records
• Conducting active case investigation and monitoring newly diagnosed patients
• Analysing the geographical and temporal distribution of reported cases
• Advising residents, workers, and visitors with compatible symptoms to seek medical care promptly
• Providing public information regarding symptoms, transmission, and risk factors
• Continuing confirmatory laboratory testing to support source identification

Residents, workers, and visitors who have been in the affected Upper East Side area since late June 2026 and develop fever, cough, shortness of breath, or other pneumonia-like symptoms should contact a healthcare provider promptly.

About Legionnaires' Disease

Legionnaires' disease is a serious form of bacterial pneumonia caused by Legionella bacteria. Infection generally occurs when a person breathes in tiny droplets or mist containing the bacteria.

In general, Legionnaires' disease is not transmitted directly from one person to another. It is also not usually acquired by drinking contaminated water. The principal risk occurs when contaminated water becomes aerosolized and the resulting droplets are inhaled.

Legionella bacteria occur naturally in freshwater environments but may multiply to harmful levels in human-made water systems, particularly when water is warm, stagnant, or inadequately disinfected.

Potential sources include:

• Cooling towers
• Large building plumbing systems
• Hot-water tanks and heaters
• Showers and faucets
• Hot tubs and spas
• Decorative fountains and water features
• Respiratory therapy equipment containing contaminated water
• Other devices that produce water mist or aerosols

People at Increased Risk

Most healthy people exposed to Legionella bacteria do not develop Legionnaires' disease. However, the risk of infection and severe illness is higher among:

• Adults aged 50 years and older
• Current or former smokers
• People with chronic lung diseases, including chronic obstructive pulmonary disease or emphysema
• People with weakened immune systems
• People receiving immunosuppressive medicines
• People with cancer
• People who have received an organ transplant
• People with underlying conditions such as diabetes, kidney failure, or liver failure

Individuals in these higher-risk groups should seek prompt medical evaluation if they develop compatible symptoms after possible exposure.

Symptoms

Legionnaires' disease produces symptoms similar to other forms of pneumonia. Common symptoms include:

• Fever
• Cough
• Shortness of breath or difficulty breathing
• Muscle aches
• Headache
• Chills
• Chest discomfort
• Fatigue or weakness
• Occasionally diarrhoea, nausea, or other gastrointestinal symptoms
• Occasionally confusion or changes in mental status

Symptoms usually develop approximately 2–14 days after exposure to Legionella bacteria, although longer incubation periods may occasionally occur.

Because the symptoms can resemble influenza, COVID-19, or other forms of pneumonia, laboratory testing is required to determine whether a patient has Legionnaires' disease.

Diagnosis

A healthcare provider may use clinical examination, medical history, imaging, and laboratory testing to diagnose Legionnaires' disease.

Diagnostic evaluation may include:

• Chest X-ray or other imaging to confirm pneumonia
• Legionella urinary antigen testing
• Culture of sputum or other lower-respiratory specimens
• Molecular testing of respiratory specimens
• Review of recent travel, workplace, residential, or environmental exposure

The Centers for Disease Control and Prevention recommends pairing a urinary antigen test with culture or molecular testing of a lower-respiratory specimen whenever clinically appropriate.

Treatment

There is currently no vaccine for Legionnaires' disease. The disease requires prompt treatment with appropriate antibiotics prescribed by a qualified healthcare professional. Early diagnosis and treatment can improve the likelihood of recovery and reduce the risk of serious complications.

Antibiotics that may be used by clinicians include:

• Azithromycin or another appropriate macrolide antibiotic
• Levofloxacin or moxifloxacin, which are respiratory fluoroquinolone antibiotics

The selection of an antibiotic, dosage, route of administration, and duration of treatment depends on the patient's clinical condition, underlying illnesses, medication history, local clinical guidelines, and the treating physician's assessment.

Patients with severe disease may require:

• Hospitalization
• Intravenous antibiotic therapy
• Oxygen therapy
• Intravenous fluids
• Respiratory support
• Monitoring and treatment of complications

Medical advisory: Antibiotics should only be taken under the direction of a qualified healthcare professional. Self-medication or delayed medical evaluation may lead to complications or inappropriate treatment.

Prevention and Control Measures

Prevention primarily depends on controlling the growth and spread of Legionella bacteria in building water systems and devices that generate water mist.

Recommended prevention and control measures include:

• Regular inspection, maintenance, cleaning, and disinfection of cooling towers
• Implementation of comprehensive water-management programmes in large buildings
• Routine monitoring of water temperature and disinfectant levels
• Prevention of water stagnation in building plumbing systems
• Regular cleaning and maintenance of hot tubs, decorative fountains, and similar water systems
• Prompt testing and remediation when Legionella contamination is suspected or detected
• Maintenance of accurate cooling-tower testing and servicing records
• Compliance with applicable cooling-tower registration, inspection, and reporting requirements
• Rapid investigation of suspected cases and clusters
• Prompt medical evaluation for individuals who develop compatible symptoms following possible exposure

Building owners and facility managers should maintain an effective water-management programme based on the characteristics of their water systems, building population, and applicable public health requirements.

Advice for Residents and Visitors

• Seek medical care promptly if you develop fever, cough, shortness of breath, or other pneumonia-like symptoms after being in the affected area.
• Tell the healthcare provider when and where you may have been exposed.
• People aged 50 years and older, smokers, and individuals with chronic illnesses or weakened immunity should be particularly cautious.
• Do not take antibiotics without a medical prescription.
• Follow updates and health advisories issued by the New York City Health Department.
• Call emergency medical services immediately if severe breathing difficulty, bluish lips, severe confusion, chest pain, or loss of consciousness occurs.

The New York City Health Department has stated that ordinary drinking water and conventional window or household air-conditioning units are not considered the source of this cooling-tower-associated outbreak.