What Is Legionnaires’ Disease? Causes, Symptoms, Prevention & Treatment

Legionnaires’ disease is a severe form of pneumonia caused by the Legionella bacteria, often found in freshwater environments such as lakes and streams. However, it becomes a health threat when the bacteria grow and spread in man-made water systems, including cooling towers, hot tubs, and large plumbing systems.

Although rare, it can be deadly — especially for people with weakened immune systems or existing lung conditions. In this post, we’ll dive deep into Legionnaires’ disease, including how it spreads, symptoms to watch for, and steps you can take to prevent it.

What Causes Legionnaires’ Disease?

The primary culprit is the Legionella pneumophila bacteria. These bacteria thrive in warm water systems, making certain environments more prone to contamination.

Common Sources of Legionella Bacteria

Hot water tanks and heaters
Cooling towers in HVAC systems
Decorative fountains
Hot tubs that are not properly disinfected
Large plumbing systems in hospitals, hotels, and cruise ships
Showerheads and faucets
Air humidifiers and mist machines

People can get Legionnaires’ disease by inhaling tiny water droplets (aerosols) that contain the bacteria. It is not contagious — person-to-person transmission is extremely rare.

Who Is at Risk of Getting Legionnaires’ Disease?

Anyone can get Legionnaires’ disease, but some groups are at higher risk, including:

Adults over the age of 50
Smokers
People with chronic lung disease (like COPD)
Immunocompromised individuals (e.g., cancer patients, transplant recipients)
People with diabetes or kidney disease
People taking corticosteroids or immunosuppressive drugs

Symptoms of Legionnaires’ Disease

Legionnaires’ disease usually develops 2 to 10 days after exposure. The symptoms are similar to severe pneumonia and may include:

Early Symptoms

Headache
Muscle aches
Fatigue
High fever (often over 104°F / 40°C)
Chills

H3: Later Symptoms (as the illness progresses)

Cough (can be dry or with mucus)
Shortness of breath
Chest pain
Nausea, vomiting, or diarrhea
Confusion or mental changes (especially in older adults)

If left untreated, the disease can worsen rapidly and lead to respiratory failure, sepsis, or multi-organ failure.

How Is Legionnaires’ Disease Diagnosed?

Legionnaires’ disease can be difficult to distinguish from other forms of pneumonia. That’s why early and accurate diagnosis is crucial. Diagnostic methods include:

Urine antigen test – detects Legionella antigens in urine
Sputum culture – tests mucus from lungs for Legionella bacteria
Chest X-ray – shows signs of pneumonia
Blood tests – to check for infection and organ function

Treatment for Legionnaires’ Disease

Legionnaires’ disease is treatable with antibiotics, especially if caught early. Doctors typically prescribe:

Azithromycin or
Levofloxacin

Most healthy people recover completely with proper medical care, but hospitalization is common, especially in severe cases.

Recovery Timeline

Mild cases: 1–2 weeks
Severe cases: Recovery may take months, especially for those with pre-existing health conditions.

How to Prevent Legionnaires’ Disease

Since the disease originates from man-made water systems, prevention depends on managing and maintaining those systems properly.

Key Prevention Tips

Regular maintenance of water systems in hotels, hospitals, and commercial buildings
Disinfection of cooling towers and water storage tanks
Frequent cleaning of humidifiers, fountains, and hot tubs
Ensuring hot water is stored at a high enough temperature (above 60°C or 140°F)
Flushing unused water systems in buildings that are vacant or underused

Building owners and facility managers must follow Legionella water safety plans and local health department guidelines to prevent outbreaks.

Recent Legionnaires’ Disease Outbreaks

Legionnaires’ disease outbreaks often occur in:

Hotels and resorts
Long-term care facilities
Cruise ships
Hospitals
Office buildings

For example, in recent years, several U.S. cities and European countries have reported outbreaks traced back to poorly maintained cooling towers or contaminated spa facilities.

Pro tip: If you’re staying in a hotel or traveling, avoid using hot tubs or showers in facilities that appear poorly maintained.

Is Legionnaires’ Disease a Public Health Concern?

Yes. The CDC estimates about 10,000 cases are reported annually in the United States, but the actual number may be much higher due to underdiagnosis.

Health agencies worldwide monitor and investigate outbreaks to contain the disease, and some regions even require mandatory reporting.

Final Thoughts on Legionnaires’ Disease

Legionnaires’ disease is rare but serious. Fortunately, it’s highly preventable and treatable if recognized early. Awareness is the first step toward prevention — both for individuals and businesses that operate water systems.

If you or a loved one experience symptoms of pneumonia after staying in a hotel, hospital, or using a public hot tub, seek medical attention immediately.

Internal Resources You May Find Useful

Frequently Asked Questions (FAQ)

Can Legionnaires’ disease be spread from person to person?

Extremely rarely. It is primarily transmitted through inhalation of contaminated water droplets.

How long does it take to recover?

With treatment, most people recover in 1–3 weeks, though fatigue and weakness may last longer.

Can I get it from drinking water?

Drinking water contaminated with Legionella is not typically a source of infection unless it goes “down the wrong pipe” into the lungs.

Is Legionnaires’ disease deadly?

Yes, it can be — especially if untreated. The fatality rate is estimated at 10%, but can be higher in outbreaks or among vulnerable populations.

The post What Is Legionnaires’ Disease? Causes, Symptoms, Prevention & Treatment appeared first on NSF News and Magazine.