Legionnaires Disease: Symptoms, Causes & Treatment

Legionnaires' disease is a serious lung infection caused by Legionella pneumophila bacteria and is a type of bacterial pneumonia. It can lead to symptoms like high fever, cough, chest pain, and difficulty breathing, which may worsen quickly without treatment.

Legionnaires' disease spreads through inhaling contaminated water droplets from sources like air conditioning systems, hot tubs, or humidifiers. The bacteria grow in warm, moist environments, increasing the risk of exposure in certain settings.

Treatment for Legionnaires' disease usually involves antibiotics and often requires hospital care, especially in more severe cases. Early diagnosis is important to prevent complications such as respiratory failure, particularly in older adults, smokers, or people with weakened immune systems.

Main symptoms

The most common symptoms of Legionnaires' disease include:

• Chest pain

• High fever

• Dry cough, which may contain blood

• Difficulty breathing and shortness of breath

• Chills

• General malaise or fatigue

• Headache

• Vomiting, abdominal pain, and diarrhea

According to the CDC, symptoms of Legionnaires’ disease usually begin within 2 to 14 days after exposure to Legionella bacteria.

If signs of infection develop, it is important to see your primary care provider or a pulmonologist (lung specialist) to confirm the diagnosis and start the right treatment.

Getting medical care early helps reduce the risk of serious complications, such as respiratory failure.

Legionella and bacterial pneumonia

Legionella pneumophila causes a severe type of bacterial pneumonia. It is one of the leading causes of community-acquired and hospital-acquired pneumonia.

Confirming a diagnosis

Legionnaires’ disease is usually diagnosed by a pulmonologist, primary care provider, or infectious disease specialist. The assessment includes reviewing your symptoms and medical history and performing a physical exam, which involves listening to your lungs with a stethoscope.

To confirm the diagnosis, the provider may also order tests such as a chest X-ray, a sputum culture, and a complete blood count (CBC). These tests help evaluate lung health and overall condition, and can detect the presence of Legionella pneumophila bacteria.

Transmission and spread

Legionella pneumophila spreads when a person inhales tiny water droplets (aerosols) that contain the bacteria. Once in the lungs, the bacteria can multiply in the respiratory tract and cause an infection.

The bacteria grow easily in warm, humid environments and can be found in places such as:

• Stagnant water, especially where algae or moss are present

• Dirty water tanks

• Puddles or other standing water

• Damp soil

• Air conditioning systems or filters

• Humidifiers

• Vaporizers

• Saunas or spas

According to the CDC and the WHO, inhaling contaminated aerosolized water is the most common way Legionella spreads, especially from sources such as hot tubs, humidifiers, and air-conditioning or building water systems.

Although inhalation is the most common route of transmission, infection can also occur when swimming in contaminated rivers, lakes, or pools.

Anyone can be affected, but it is more common in older adults, smokers, and people with weakened immune systems due to chronic conditions such as emphysema, asthma, diabetes, or liver failure.

Treatment options

Treatment for Legionella pneumophila infection should be guided by a pulmonologist, primary care provider, or infectious disease specialist, and will vary according to how severe the symptoms are.

In most cases, hospital care is required, which may include antibiotics, intravenous (IV) fluids, and oxygen therapy to help with breathing.

Commonly prescribed antibiotics for Legionnaires' disease include ciprofloxacin, azithromycin, levofloxacin, and erythromycin. Treatment usually lasts 7 to 10 days, and the length of the hospital stay depends on how well the person responds to therapy.

Some cases resolve within 10 days, but recovery may take longer in people who are older, smoke, have other respiratory diseases, or have weakened immune systems.

Prevention measures

To help prevent Legionella pneumophila infection, the following precautions are recommended:

• Avoid taking very hot showers or baths, especially in public places like gyms or hotels.

• Do not use hot tubs or spas that haven’t been cleaned in a long time.

• When using a bathtub, turn on the water slowly to reduce spray pressure.

• Clean the air conditioning filters and drip trays with a water and chlorine solution every 6 months.

• Soak shower heads in a chlorine solution to disinfect them.

• Clean water tanks regularly and as needed.

These precautions are especially important during a Legionella outbreak. However, it is also essential to avoid stagnant water and regularly disinfect household water systems at all times.