From the Guidelines
Legionnaires' pneumonia is caused by bacteria called Legionella, primarily Legionella pneumophila, which thrives in warm water environments and infects people when they inhale small droplets of water containing the bacteria. This bacterium is commonly found in cooling towers, hot tubs, decorative fountains, and complex plumbing systems 1. People become infected when they inhale small droplets of water containing the bacteria, and the bacteria cannot spread from person to person. Risk factors for Legionnaires' disease include being over 50 years old, having a weakened immune system, smoking, and having chronic lung disease 1.
Key Points
- The bacteria infect the lungs by attaching to alveolar macrophages, replicating inside them, and eventually destroying these immune cells, triggering inflammation in the lungs and leading to symptoms of pneumonia 1.
- Legionnaires' disease typically causes high fever, cough, shortness of breath, muscle aches, and headaches.
- Treatment usually involves antibiotics such as azithromycin (500mg daily for 7-10 days) or fluoroquinolones like levofloxacin (750mg daily for 7-10 days), and early diagnosis and treatment are essential as the disease can be severe, particularly in vulnerable populations 1.
Diagnosis and Treatment
- The preferred diagnostic tests are the urinary antigen assay and culture of respiratory secretions on selective media 1.
- Testing for Legionella species is appropriate for any patient hospitalized with enigmatic pneumonia, and treatment should be initiated as rapidly as is feasible 1.
- The preferred treatment for legionnaires’ disease for hospitalized patients is azithromycin or a fluoroquinolone, and for patients who do not require hospitalization, acceptable antibiotics include erythromycin, doxycycline, azithromycin, clarithromycin, or a fluoroquinolone 1.
From the Research
Causes of Legionnaires' Pneumonia
- Legionnaires' pneumonia is caused by the bacterium Legionella pneumophila 2, 3, 4, 5, 6
- The bacterium is primarily an intracellular pathogen and requires treatment with antibiotics that can efficiently enter the intracellular space 4
Transmission and Risk Factors
- Legionnaires' disease can be acquired through inhalation of aerosolized water containing Legionella bacteria 3
- The disease can be community-acquired or hospital-acquired, and the risk factors include exposure to contaminated water sources 3, 5
Clinical Manifestations
- The clinical manifestations of Legionnaires' disease are nonspecific and can include symptoms such as pneumonia, fever, and respiratory failure 3, 4, 5
- The disease can be severe and requires early intervention and treatment with effective antibiotics 4, 5, 6
Treatment Options
- Azithromycin and levofloxacin are considered first-line therapies for the treatment of Legionnaires' disease 3, 6
- Other effective antibiotics include tetracyclines, tigecycline, and other fluoroquinolones and macrolides 3, 5
- Monotherapy is preferred to double-drug therapy, and doxycycline or a respiratory quinolone can provide optimal cost-effective therapy 5