Introduction
Legionnaires’ disease is a serious type of pneumonia caused by infection with Legionella bacteria. The illness is named after an outbreak at an American Legion convention in 1976, but cases now occur worldwide. Legionnaires’ disease most commonly affects older adults, smokers, and people with weakened immune systems. Prompt diagnosis and treatment are essential, as the disease can be life-threatening if not managed properly.
Causes
Legionnaires’ disease is caused by inhaling water droplets contaminated with Legionella bacteria. These bacteria thrive in warm, stagnant water and can multiply in man-made water systems such as hot tubs, cooling towers, air conditioning units, decorative fountains, and plumbing systems. People become infected by breathing in mist or vapor containing the bacteria, but the disease does not spread from person to person. Risk factors include older age, smoking, chronic lung disease, and conditions or medications that weaken the immune system.
Symptoms
Symptoms of Legionnaires’ disease usually develop 2 to 10 days after exposure to the bacteria. Early symptoms resemble the flu and may include fever, chills, headache, muscle aches, and fatigue. As the disease progresses, symptoms can become more severe and include a high fever, cough (which may produce mucus or blood), shortness of breath, chest pain, nausea, vomiting, diarrhea, and confusion. In severe cases, complications such as respiratory failure, septic shock, and multi-organ dysfunction can occur.
Diagnosis
Diagnosis of Legionnaires’ disease involves a combination of clinical evaluation and laboratory testing. A healthcare provider will assess symptoms and medical history, and may order a chest X-ray to look for pneumonia. Laboratory tests include urine antigen testing for Legionella, sputum cultures, and blood tests to confirm the presence of the bacteria and assess organ function. Early and accurate diagnosis is crucial for effective treatment.
Treatment Options
Legionnaires’ disease is treated with antibiotics, most commonly macrolides (such as azithromycin) or fluoroquinolones (such as levofloxacin). Early initiation of antibiotic therapy is important for a good outcome. Supportive care, such as oxygen therapy, intravenous fluids, and treatment of complications, may be required in severe cases. Hospitalization is often necessary, especially for people with underlying health conditions or severe symptoms.
Prevention
Preventing Legionnaires’ disease focuses on controlling the growth of Legionella bacteria in water systems. Regular maintenance, cleaning, and disinfection of water systems in buildings, hotels, hospitals, and public facilities are essential. Water temperature should be kept outside the range in which Legionella thrives (20–50°C or 68–122°F). Individuals at higher risk should avoid exposure to potentially contaminated water sources, such as hot tubs or decorative fountains, especially if maintenance is uncertain.
When to Seek Medical Care
Seek medical attention promptly if you develop symptoms of pneumonia—such as high fever, cough, shortness of breath, or chest pain—especially if you are at higher risk or have recently been exposed to water systems that may harbor Legionella. Early treatment can prevent serious complications and improve outcomes.
Takeaway
Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria found in contaminated water systems. Early recognition, prompt antibiotic treatment, and preventive measures are key to reducing the risk and severity of the disease. If you experience symptoms after possible exposure, seek medical care without delay.